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Merge branch 'docs/sentinel' into 'master' 

Add Redis Sentinel HA docs (port from CE)

See merge request !884
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doc/administration/high_availability/README.md
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......@@ -7,19 +7,10 @@ highly available.
## Architecture
### Active/Passive
For pure high-availability/failover with no scaling you can use an
active/passive configuration. This utilizes DRBD (Distributed Replicated
Block Device) to keep all data in sync. DRBD requires a low latency link to
remain in sync. It is not advisable to attempt to run DRBD between data centers
or in different cloud availability zones.
There are two kinds of setups:
Components/Servers Required:
- 2 servers/virtual machines (one active/one passive)
![Active/Passive HA Diagram](../img/high_availability/active-passive-diagram.png)
- active/active
- active/passive
### Active/Active
......@@ -28,12 +19,24 @@ user requests simultaneously. The database, Redis, and GitLab application are
all deployed on separate servers. The configuration is **only** highly-available
if the database, Redis and storage are also configured as such.
![Active/Active HA Diagram](../img/high_availability/active-active-diagram.png)
**Steps to configure active/active:**
Follow the steps below to configure an active/active setup:
1. [Configure the database](database.md)
1. [Configure Redis](redis.md)
1. [Configure NFS](nfs.md)
1. [Configure the GitLab application servers](gitlab.md)
1. [Configure the load balancers](load_balancer.md)
![Active/Active HA Diagram](../img/high_availability/active-active-diagram.png)
### Active/Passive
For pure high-availability/failover with no scaling you can use an
active/passive configuration. This utilizes DRBD (Distributed Replicated
Block Device) to keep all data in sync. DRBD requires a low latency link to
remain in sync. It is not advisable to attempt to run DRBD between data centers
or in different cloud availability zones.
Components/Servers Required: 2 servers/virtual machines (one active/one passive)
![Active/Passive HA Diagram](../img/high_availability/active-passive-diagram.png)
doc/administration/high_availability/redis.md
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# Configuring Redis for GitLab HA
You can choose to install and manage Redis yourself, or you can use the one
that comes bundled with GitLab Omnibus packages.
> **Note:** Redis does not require authentication by default. See
>
Experimental Redis Sentinel support was [Introduced][ce-1877] in GitLab 8.11.
Starting with 8.14, Redis Sentinel is no longer experimental.
If you've used it with versions `< 8.14` before, please check the updated
documentation here.
High Availability with [Redis] is possible using a **Master** x **Slave**
topology with a [Redis Sentinel][sentinel] service to watch and automatically
start the failover procedure.
You can choose to install and manage Redis and Sentinel yourself, use
a hosted cloud solution or you can use the one that comes bundled with
Omnibus GitLab packages.
> **Notes:**
- Redis requires authentication for High Availability. See
[Redis Security](http://redis.io/topics/security) documentation for more
information. We recommend using a combination of a Redis password and tight
firewall rules to secure your Redis service.
- You are highly encouraged to read the [Redis Sentinel][sentinel] documentation
before configuring Redis HA with GitLab to fully understand the topology and
architecture.
- This is the documentation for the Omnibus GitLab packages. For installations
from source, follow the [Redis HA source installation](redis_source.md) guide.
- Redis Sentinel daemon is bundled with Omnibus GitLab Enterprise Edition only.
For configuring Sentinel with the Omnibus GitLab Community Edition and
installations from source, read the
[Available configuration setups](#available-configuration-setups) section
below.
## Overview
Before diving into the details of setting up Redis and Redis Sentinel for HA,
make sure you read this Overview section to better understand how the components
are tied together.
You need at least `3` independent machines: physical, or VMs running into
distinct physical machines. It is essential that all master and slaves Redis
instances run in different machines. If you fail to provision the machines in
that specific way, any issue with the shared environment can bring your entire
setup down.
It is OK to run a Sentinel along with a master or slave Redis instance.
No more than one Sentinel in the same machine though.
You also need to take in consideration the underlying network topology,
making sure you have redundant connectivity between Redis / Sentinel and
GitLab instances, otherwise the networks will become a single point of
failure.
Make sure that you read this document once as a whole before configuring the
components below.
### High Availability with Sentinel
>**Notes:**
- Starting with GitLab `8.11`, you can configure a list of Redis Sentinel
servers that will monitor a group of Redis servers to provide failover support.
- Starting with GitLab `8.14`, the Omnibus GitLab Enterprise Edition package
comes with Redis Sentinel daemon built-in.
High Availability with Redis requires a few things:
- Multiple Redis instances
- Run Redis in a **Master** x **Slave** topology
- Multiple Sentinel instances
- Application support and visibility to all Sentinel and Redis instances
Redis Sentinel can handle the most important tasks in an HA environment and that's
to help keep servers online with minimal to no downtime. Redis Sentinel:
- Monitors **Master** and **Slaves** instances to see if they are available
- Promotes a **Slave** to **Master** when the **Master** fails
- Demotes a **Master** to **Slave** when the failed **Master** comes back online
(to prevent data-partitioning)
- Can be queried by the application to always connect to the current **Master**
server
When a **Master** fails to respond, it's the application's responsibility
(in our case GitLab) to handle timeout and reconnect (querying a **Sentinel**
for a new **Master**).
## Configure your own Redis server
To get a better understanding on how to correctly setup Sentinel, please read
the [Redis Sentinel documentation](http://redis.io/topics/sentinel) first, as
failing to configure it correctly can lead to data loss or can bring your
whole cluster down, invalidating the failover effort.
If you're hosting GitLab on a cloud provider, you can optionally use a
managed service for Redis. For example, AWS offers a managed ElastiCache service
that runs Redis.
### Recommended setup
## Configure Redis using Omnibus
For a minimal setup, you will install the Omnibus GitLab package in `3`
**independent** machines, both with **Redis** and **Sentinel**:
If you don't want to bother setting up your own Redis server, you can use the
one bundled with Omnibus. In this case, you should disable all services except
Redis.
- Redis Master + Sentinel
- Redis Slave + Sentinel
- Redis Slave + Sentinel
1. Download/install GitLab Omnibus using **steps 1 and 2** from
[GitLab downloads](https://about.gitlab.com/downloads). Do not complete other
steps on the download page.
1. Create/edit `/etc/gitlab/gitlab.rb` and use the following configuration.
Be sure to change the `external_url` to match your eventual GitLab front-end
URL:
If you are not sure or don't understand why and where the amount of nodes come
from, read [Redis setup overview](#redis-setup-overview) and
[Sentinel setup overview](#sentinel-setup-overview).
```ruby
external_url 'https://gitlab.example.com'
# Disable all services except Redis
redis['enable'] = true
bootstrap['enable'] = false
nginx['enable'] = false
unicorn['enable'] = false
sidekiq['enable'] = false
postgresql['enable'] = false
gitlab_workhorse['enable'] = false
mailroom['enable'] = false
# Redis configuration
redis['port'] = 6379
redis['bind'] = '0.0.0.0'
For a recommended setup that can resist more failures, you will install
the Omnibus GitLab package in `5` **independent** machines, both with
**Redis** and **Sentinel**:
# If you wish to use Redis authentication (recommended)
redis['password'] = 'Redis Password'
```
- Redis Master + Sentinel
- Redis Slave + Sentinel
- Redis Slave + Sentinel
- Redis Slave + Sentinel
- Redis Slave + Sentinel
1. Run `sudo touch /etc/gitlab/skip-auto-migrations` to prevent database migrations
from running on upgrade. Only the primary GitLab application server should
handle migrations.
### Redis setup overview
1. Run `sudo gitlab-ctl reconfigure` to install and configure Redis.
You must have at least `3` Redis servers: `1` Master, `2` Slaves, and they
need to be each in a independent machine (see explanation above).
> **Note**: This `reconfigure` step will result in some errors.
That's OK - don't be alarmed.
You can have additional Redis nodes, that will help survive a situation
where more nodes goes down. Whenever there is only `2` nodes online, a failover
will not be initiated.
## Experimental Redis Sentinel support
As an example, if you have `6` Redis nodes, a maximum of `3` can be
simultaneously down.
> [Introduced][ce-1877] in GitLab 8.11.
Please note that there are different requirements for Sentinel nodes.
If you host them in the same Redis machines, you may need to take
that restrictions into consideration when calculating the amount of
nodes to be provisioned. See [Sentinel setup overview](#sentinel-setup-overview)
documentation for more information.
Since GitLab 8.11, you can configure a list of Redis Sentinel servers that
will monitor a group of Redis servers to provide you with a standard failover
support.
All Redis nodes should be configured the same way and with similar server specs, as
in a failover situation, any **Slave** can be promoted as the new **Master** by
the Sentinel servers.
There is currently one exception to the Sentinel support: `mail_room`, the
component that processes incoming emails. It doesn't support Sentinel yet, but
we hope to integrate a future release that does support it.
The replication requires authentication, so you need to define a password to
protect all Redis nodes and the Sentinels. They will all share the same
password, and all instances must be able to talk to
each other over the network.
To get a better understanding on how to correctly setup Sentinel, please read
the [Redis Sentinel documentation](http://redis.io/topics/sentinel) first, as
failing to configure it correctly can lead to data loss.
### Sentinel setup overview
The configuration consists of three parts:
Sentinels watch both other Sentinels and Redis nodes. Whenever a Sentinel
detects that a Redis node is not responding, it will announce that to the
other Sentinels. They have to reach the **quorum**, that is the minimum amount
of Sentinels that agrees a node is down, in order to be able to start a failover.
- Redis setup
- Sentinel setup
- GitLab setup
Whenever the **quorum** is met, the **majority** of all known Sentinel nodes
need to be available and reachable, so that they can elect the Sentinel **leader**
who will take all the decisions to restore the service availability by:
Read carefully how to configure those components below.
- Promoting a new **Master**
- Reconfiguring the other **Slaves** and make them point to the new **Master**
- Announce the new **Master** to every other Sentinel peer
- Reconfigure the old **Master** and demote to **Slave** when it comes back online
### Redis setup
You must have at least `3` Redis Sentinel servers, and they need to
be each in a independent machine (that are believed to fail independently),
ideally in different geographical areas.
You must have at least 2 Redis servers: 1 Master, 1 or more Slaves.
They should be configured the same way and with similar server specs, as
in a failover situation, any Slave can be elected as the new Master by
the Sentinel servers.
You can configure them in the same machines where you've configured the other
Redis servers, but understand that if a whole node goes down, you loose both
a Sentinel and a Redis instance.
In a minimal setup, the only required change for the slaves in `redis.conf`
is the addition of a `slaveof` line pointing to the initial master.
You can increase the security by defining a `requirepass` configuration in
the master, and `masterauth` in slaves.
The number of sentinels should ideally always be an **odd** number, for the
consensus algorithm to be effective in the case of a failure.
---
In a `3` nodes topology, you can only afford `1` Sentinel node going down.
Whenever the **majority** of the Sentinels goes down, the network partition
protection prevents destructive actions and a failover **will not be started**.
**Configuring your own Redis server**
Here are some examples:
1. Add to the slaves' `redis.conf`:
- With `5` or `6` sentinels, a maximum of `2` can go down for a failover begin.
- With `7` sentinels, a maximum of `3` nodes can go down.
```conf
# IP and port of the master Redis server
slaveof 10.10.10.10 6379
```
The **Leader** election can sometimes fail the voting round when **consensus**
is not achieved (see the odd number of nodes requirement above). In that case,
a new attempt will be made after the amount of time defined in
`sentinel['failover_timeout']` (in milliseconds).
1. Optionally, set up password authentication for increased security.
Add the following to master's `redis.conf`:
>**Note:**
We will see where `sentinel['failover_timeout']` is defined later.
The `failover_timeout` variable has a lot of different use cases. According to
the official documentation:
- The time needed to re-start a failover after a previous failover was
already tried against the same master by a given Sentinel, is two
times the failover timeout.
- The time needed for a slave replicating to a wrong master according
to a Sentinel current configuration, to be forced to replicate
with the right master, is exactly the failover timeout (counting since
the moment a Sentinel detected the misconfiguration).
- The time needed to cancel a failover that is already in progress but
did not produced any configuration change (SLAVEOF NO ONE yet not
acknowledged by the promoted slave).
- The maximum time a failover in progress waits for all the slaves to be
reconfigured as slaves of the new master. However even after this time
the slaves will be reconfigured by the Sentinels anyway, but not with
the exact parallel-syncs progression as specified.
### Available configuration setups
Based on your infrastructure setup and how you have installed GitLab, there are
multiple ways to configure Redis HA. Omnibus GitLab packages have Redis and/or
Redis Sentinel bundled with them so you only need to focus on configuration.
Pick the one that suits your needs.
- [Installations from source][source]: You need to install Redis and Sentinel
yourself. Use the [Redis HA installation from source](redis_source.md)
documentation.
- [Omnibus GitLab **Community Edition** (CE) package][ce]: Redis is bundled, so you
can use the package with only the Redis service enabled as described in steps
1 and 2 of this document (works for both master and slave setups). To install
and configure Sentinel, jump directly to the Sentinel section in the
[Redis HA installation from source](redis_source.md#step-3-configuring-the-redis-sentinel-instances) documentation.
- [Omnibus GitLab **Enterprise Edition** (EE) package][ee]: Both Redis and Sentinel
are bundled in the package, so you can use the EE package to setup the whole
Redis HA infrastructure (master, slave and Sentinel) which is described in
this document.
- If you have installed GitLab using the Omnibus GitLab packages (CE or EE),
but you want to use your own external Redis server, follow steps 1-3 in the
[Redis HA installation from source](redis_source.md) documentation, then go
straight to step 4 in this guide to
[set up the GitLab application](#step-4-configuring-the-gitlab-application).
## Configuring Redis HA
This is the section where we install and setup the new Redis instances.
>**Notes:**
- We assume that you install GitLab and all HA components from scratch. If you
already have it installed and running, read how to
[switch from a single-machine installation to Redis HA](#switching-from-an-existing-single-machine-installation-to-redis-ha).
- Redis nodes (both master and slaves) will need the same password defined in
`redis['password']`. At any time during a failover the Sentinels can
reconfigure a node and change its status from master to slave and vice versa.
### Prerequisites
The prerequisites for a HA Redis setup are the following:
1. Provision the minimum required number of instances as specified in the
[recommended setup](#recommended-setup) section.
1. **Do NOT** install Redis or Redis Sentinel in the same machines your
GitLab application is running on. You can however opt in to install Redis
and Sentinel in the same machine (each in independent ones is recommended
though).
1. All Redis nodes must be able to talk to each other and accept incoming
connections over Redis (`6379`) and Sentinel (`26379`) ports (unless you
change the default ones).
1. The server that hosts the GitLab application must be able to access the
Redis nodes.
1. Protect the nodes from access from external networks ([Internet][it]), using
firewall.
### Step 1. Configuring the master Redis instance
1. SSH into the **master** Redis server.
1. [Download/install](https://about.gitlab.com/installation) the Omnibus GitLab
package you want using **steps 1 and 2** from the GitLab downloads page.
- Make sure you select the correct Omnibus package, with the same version
and type (Community, Enterprise editions) of your current install.
- Do not complete any other steps on the download page.
1. Edit `/etc/gitlab/gitlab.rb` and add the contents:
```conf
# Optional password authentication for increased security
requirepass "<password>"
```ruby
# Enable the master role and disable all other services in the machine
# (you can still enable Sentinel).
redis_master_role['enable'] = true
# IP address pointing to a local IP that the other machines can reach to.
# You can also set bind to '0.0.0.0' which listen in all interfaces.
# If you really need to bind to an external accessible IP, make
# sure you add extra firewall rules to prevent unauthorized access.
redis['bind'] = '10.0.0.1'
# Define a port so Redis can listen for TCP requests which will allow other
# machines to connect to it.
redis['port'] = 6379
# Set up password authentication for Redis (use the same password in all nodes).
redis['password'] = 'redis-password-goes-here'
```
1. Then add this line to all the slave servers' `redis.conf`:
1. To prevent database migrations from running on upgrade, run:
```conf
masterauth "<password>"
```
sudo touch /etc/gitlab/skip-auto-migrations
```
1. Restart the Redis services for the changes to take effect.
Only the primary GitLab application server should handle migrations.
---
1. [Reconfigure Omnibus GitLab][reconfigure] for the changes to take effect.
### Step 2. Configuring the slave Redis instances
**Using Redis via Omnibus**
1. SSH into the **slave** Redis server.
1. [Download/install](https://about.gitlab.com/installation) the Omnibus GitLab
package you want using **steps 1 and 2** from the GitLab downloads page.
- Make sure you select the correct Omnibus package, with the same version
and type (Community, Enterprise editions) of your current install.
- Do not complete any other steps on the download page.
1. Edit `/etc/gitlab/gitlab.rb` of a master Redis machine (usualy a single machine):
1. Edit `/etc/gitlab/gitlab.rb` and add the contents:
```ruby
## Redis TCP support (will disable UNIX socket transport)
redis['bind'] = '0.0.0.0' # or specify an IP to bind to a single one
# Enable the slave role and disable all other services in the machine
# (you can still enable Sentinel). This will also set automatically
# `redis['master'] = false`.
redis_slave_role['enable'] = true
# IP address pointing to a local IP that the other machines can reach to.
# You can also set bind to '0.0.0.0' which listen in all interfaces.
# If you really need to bind to an external accessible IP, make
# sure you add extra firewall rules to prevent unauthorized access.
redis['bind'] = '10.0.0.2'
# Define a port so Redis can listen for TCP requests which will allow other
# machines to connect to it.
redis['port'] = 6379
## Master redis instance
redis['password'] = '<huge password string here>'
```
# The same password for Redeis authentication you set up for the master node.
redis['password'] = 'redis-password-goes-here'
1. Edit `/etc/gitlab/gitlab.rb` of a slave Redis machine (should be one or more machines):
# The IP of the master Redis node.
redis['master_ip'] = '10.0.0.1'
```ruby
## Redis TCP support (will disable UNIX socket transport)
redis['bind'] = '0.0.0.0' # or specify an IP to bind to a single one
redis['port'] = 6379
# Port of master Redis server, uncomment to change to non default. Defaults
# to `6379`.
#redis['master_port'] = 6379
```
1. To prevent database migrations from running on upgrade, run:
## Slave redis instance
redis['master_ip'] = '10.10.10.10' # IP of master Redis server
redis['master_port'] = 6379 # Port of master Redis server
redis['master_password'] = "<huge password string here>"
```
sudo touch /etc/gitlab/skip-auto-migrations
```
Only the primary GitLab application server should handle migrations.
1. Reconfigure the GitLab for the changes to take effect: `sudo gitlab-ctl reconfigure`
1. [Reconfigure Omnibus GitLab][reconfigure] for the changes to take effect.
1. Go through the steps again for all the other slave nodes.
---
These values don't have to be changed again in `/etc/gitlab/gitlab.rb` after
a failover, as the nodes will be managed by the Sentinels, and even after a
`gitlab-ctl reconfigure`, they will get their configuration restored by
the same Sentinels.
### Step 3. Configuring the Redis Sentinel instances
>**Note:**
Redis Sentinel is bundled with Omnibus GitLab Enterprise Edition only. The
following section assumes you are using Omnibus GitLab Enterprise Edition.
For the Omnibus Community Edition and installations from source, follow the
[Redis HA source install](redis_source.md) guide.
Now that the Redis servers are all set up, let's configure the Sentinel
servers.
### Sentinel setup
If you are not sure if your Redis servers are working and replicating
correctly, please read the [Troubleshooting Replication](#troubleshooting-replication)
and fix it before proceeding with Sentinel setup.
We don't provide yet an automated way to setup and run the Sentinel daemon
from Omnibus installation method. You must follow the instructions below and
run it by yourself.
You must have at least `3` Redis Sentinel servers, and they need to
be each in an independent machine. You can configure them in the same
machines where you've configured the other Redis servers.
The support for Sentinel in Ruby has some [caveats](https://github.com/redis/redis-rb/issues/531).
While you can give any name for the `master-group-name` part of the
configuration, as in this example:
With GitLab Enterprise Edition, you can use the Omnibus package to setup
multiple machines with the Sentinel daemon.
```conf
sentinel monitor <master-group-name> <ip> <port> <quorum>
```
---
,for it to work in Ruby, you have to use the "hostname" of the master Redis
server, otherwise you will get an error message like:
`Redis::CannotConnectError: No sentinels available.`. Read
[Sentinel troubleshooting](#sentinel-troubleshooting) for more information.
1. SSH into the server that will host Redis Sentinel.
1. **You can omit this step if the Sentinels will be hosted in the same node as
the other Redis instances.**
Here is an example configuration file (`sentinel.conf`) for a Sentinel node:
[Download/install](https://about.gitlab.com/downloads-ee) the
Omnibus GitLab Enterprise Edition package using **steps 1 and 2** from the
GitLab downloads page.
- Make sure you select the correct Omnibus package, with the same version
the GitLab application is running.
- Do not complete any other steps on the download page.
```conf
port 26379
sentinel monitor master-redis.example.com 10.10.10.10 6379 1
sentinel down-after-milliseconds master-redis.example.com 10000
sentinel config-epoch master-redis.example.com 0
sentinel leader-epoch master-redis.example.com 0
```
1. Edit `/etc/gitlab/gitlab.rb` and add the contents (if you are installing the
Sentinels in the same node as the other Redis instances, some values might
be duplicate below):
---
```ruby
redis_sentinel_role['enable'] = true
The final part is to inform the main GitLab application server of the Redis
master and the new sentinels servers.
# Must be the same in every sentinel node
redis['master_name'] = 'gitlab-redis'
### GitLab setup
# The same password for Redis authentication you set up for the master node.
redis['password'] = 'redis-password-goes-here'
You can enable or disable sentinel support at any time in new or existing
installations. From the GitLab application perspective, all it requires is
the correct credentials for the master Redis and for a few Sentinel nodes.
# The IP of the master Redis node.
redis['master_ip'] = '10.0.0.1'
It doesn't require a list of all Sentinel nodes, as in case of a failure,
the application will need to query only one of them.
# Define a port so Redis can listen for TCP requests which will allow other
# machines to connect to it.
redis['port'] = 6379
>**Note:**
The following steps should be performed in the [GitLab application server](gitlab.md).
# Port of master Redis server, uncomment to change to non default. Defaults
# to `6379`.
#redis['master_port'] = 6379
## Configure Sentinel
sentinel['bind'] = '10.0.0.1'
# Port that Sentinel listens on, uncomment to change to non default. Defaults
# to `26379`.
# sentinel['port'] = 26379
## Quorum must reflect the amount of voting sentinels it take to start a failover.
## Value must NOT be greater then the amount of sentinels.
##
## The quorum can be used to tune Sentinel in two ways:
## 1. If a the quorum is set to a value smaller than the majority of Sentinels
## we deploy, we are basically making Sentinel more sensible to master failures,
## triggering a failover as soon as even just a minority of Sentinels is no longer
## able to talk with the master.
## 1. If a quorum is set to a value greater than the majority of Sentinels, we are
## making Sentinel able to failover only when there are a very large number (larger
## than majority) of well connected Sentinels which agree about the master being down.s
sentinel['quorum'] = 2
## Consider unresponsive server down after x amount of ms.
# sentinel['down_after_milliseconds'] = 10000
## Specifies the failover timeout in milliseconds. It is used in many ways:
##
## - The time needed to re-start a failover after a previous failover was
## already tried against the same master by a given Sentinel, is two
## times the failover timeout.
##
## - The time needed for a slave replicating to a wrong master according
## to a Sentinel current configuration, to be forced to replicate
## with the right master, is exactly the failover timeout (counting since
## the moment a Sentinel detected the misconfiguration).
##
## - The time needed to cancel a failover that is already in progress but
## did not produced any configuration change (SLAVEOF NO ONE yet not
## acknowledged by the promoted slave).
##
## - The maximum time a failover in progress waits for all the slaves to be
## reconfigured as slaves of the new master. However even after this time
## the slaves will be reconfigured by the Sentinels anyway, but not with
## the exact parallel-syncs progression as specified.
# sentinel['failover_timeout'] = 60000
```
1. To prevent database migrations from running on upgrade, run:
```
sudo touch /etc/gitlab/skip-auto-migrations
```
**For source based installations**
Only the primary GitLab application server should handle migrations.
1. Edit `/home/git/gitlab/config/resque.yml` following the example in
`/home/git/gitlab/config/resque.yml.example`, and uncomment the sentinels
line, changing to the correct server credentials.
1. Restart GitLab for the changes to take effect.
1. [Reconfigure Omnibus GitLab][reconfigure] for the changes to take effect.
1. Go through the steps again for all the other Sentinel nodes.
**For Omnibus installations**
### Step 4. Configuring the GitLab application
The final part is to inform the main GitLab application server of the Redis
Sentinels servers and authentication credentials.
You can enable or disable Sentinel support at any time in new or existing
installations. From the GitLab application perspective, all it requires is
the correct credentials for the Sentinel nodes.
While it doesn't require a list of all Sentinel nodes, in case of a failure,
it needs to access at least one of the listed.
>**Note:**
The following steps should be performed in the [GitLab application server](gitlab.md)
which ideally should not have Redis or Sentinels on it for a HA setup.
1. SSH into the server where the GitLab application is installed.
1. Edit `/etc/gitlab/gitlab.rb` and add/change the following lines:
```ruby
gitlab-rails['redis_host'] = "master-redis.example.com"
gitlab-rails['redis_port'] = 6379
gitlab-rails['redis_password'] = '<huge password string here>'
gitlab-rails['redis_sentinels'] = [
{'host' => '10.10.10.1', 'port' => 26379},
{'host' => '10.10.10.2', 'port' => 26379},
{'host' => '10.10.10.3', 'port' => 26379}
```
## Must be the same in every sentinel node
redis['master_name'] = 'gitlab-redis'
## The same password for Redis authentication you set up for the master node.
redis['password'] = 'redis-password-goes-here'
## A list of sentinels with `host` and `port`
gitlab_rails['redis_sentinels'] = [
{'host' => '10.0.0.1', 'port' => 26379},
{'host' => '10.0.0.2', 'port' => 26379},
{'host' => '10.0.0.3', 'port' => 26379}
]
```
1. [Reconfigure] the GitLab for the changes to take effect.
1. [Reconfigure Omnibus GitLab][reconfigure] for the changes to take effect.
### Sentinel troubleshooting
## Switching from an existing single-machine installation to Redis HA
If you get an error like: `Redis::CannotConnectError: No sentinels available.`,
there may be something wrong with your configuration files or it can be related
to [this issue][gh-531] ([pull request][gh-534] that should make things better).
If you already have a single-machine GitLab install running, you will need to
replicate from this machine first, before de-activating the Redis instance
inside it.
Your single-machine install will be the initial **Master**, and the `3` others
should be configured as **Slave** pointing to this machine.
It's a bit rigid the way you have to config `resque.yml` and `sentinel.conf`,
otherwise `redis-rb` will not work properly.
After replication catches up, you will need to stop services in the
single-machine install, to rotate the **Master** to one of the new nodes.
The hostname ('my-primary-redis') of the primary Redis server (`sentinel.conf`)
**must** match the one configured in GitLab (`resque.yml` for source installations
or `gitlab-rails['redis_*']` in Omnibus) and it must be valid ex:
Make the required changes in configuration and restart the new nodes again.
```conf
# sentinel.conf:
sentinel monitor my-primary-redis 10.10.10.10 6379 1
sentinel down-after-milliseconds my-primary-redis 10000
sentinel config-epoch my-primary-redis 0
sentinel leader-epoch my-primary-redis 0
To disable redis in the single install, edit `/etc/gitlab/gitlab.rb`:
```ruby
redis['enable'] = false
```
If you fail to replicate first, you may loose data (unprocessed background jobs).
## Example of a minimal configuration with 1 master, 2 slaves and 3 Sentinels
>**Note:**
Redis Sentinel is bundled with Omnibus GitLab Enterprise Edition only. For
different setups, read the
[available configuration setups](#available-configuration-setups) section.
In this example we consider that all servers have an internal network
interface with IPs in the `10.0.0.x` range, and that they can connect
to each other using these IPs.
In a real world usage, you would also setup firewall rules to prevent
unauthorized access from other machines and block traffic from the
outside (Internet).
We will use the same `3` nodes with **Redis** + **Sentinel** topology
discussed in [Redis setup overview](#redis-setup-overview) and
[Sentinel setup overview](#sentinel-setup-overview) documentation.
Here is a list and description of each **machine** and the assigned **IP**:
* `10.0.0.1`: Redis Master + Sentinel 1
* `10.0.0.2`: Redis Slave 1 + Sentinel 2
* `10.0.0.3`: Redis Slave 2 + Sentinel 3
* `10.0.0.4`: GitLab application
Please note that after the initial configuration, if a failover is initiated
by the Sentinel nodes, the Redis nodes will be reconfigured and the **Master**
will change permanently (including in `redis.conf`) from one node to the other,
until a new failover is initiated again.
The same thing will happen with `sentinel.conf` that will be overridden after the
initial execution, after any new sentinel node starts watching the **Master**,
or a failover promotes a different **Master** node.
### Example configuration for Redis master and Sentinel 1
In `/etc/gitlab/gitlab.rb`:
```ruby
redis_master_role['enable'] = true
redis_sentinel_role['enable'] = true
redis['bind'] = '10.0.0.1'
redis['port'] = 6379
redis['password'] = 'redis-password-goes-here'
redis['master_name'] = 'gitlab-redis' # must be the same in every sentinel node
redis['master_password'] = 'redis-password-goes-here' # the same value defined in redis['password'] in the master instance
redis['master_ip'] = '10.0.0.1' # ip of the initial master redis instance
#redis['master_port'] = 6379 # port of the initial master redis instance, uncomment to change to non default
sentinel['bind'] = '10.0.0.1'
# sentinel['port'] = 26379 # uncomment to change default port
sentinel['quorum'] = 2
# sentinel['down_after_milliseconds'] = 10000
# sentinel['failover_timeout'] = 60000
```
[Reconfigure Omnibus GitLab][reconfigure] for the changes to take effect.
### Example configuration for Redis slave 1 and Sentinel 2
In `/etc/gitlab/gitlab.rb`:
```ruby
redis_slave_role['enable'] = true
redis_sentinel_role['enable'] = true
redis['bind'] = '10.0.0.2'
redis['port'] = 6379
redis['password'] = 'redis-password-goes-here'
redis['master_password'] = 'redis-password-goes-here'
redis['master_ip'] = '10.0.0.1' # IP of master Redis server
#redis['master_port'] = 6379 # Port of master Redis server, uncomment to change to non default
redis['master_name'] = 'gitlab-redis' # must be the same in every sentinel node
sentinel['bind'] = '10.0.0.2'
# sentinel['port'] = 26379 # uncomment to change default port
sentinel['quorum'] = 2
# sentinel['down_after_milliseconds'] = 10000
# sentinel['failover_timeout'] = 60000
```
[Reconfigure Omnibus GitLab][reconfigure] for the changes to take effect.
### Example configuration for Redis slave 2 and Sentinel 3
In `/etc/gitlab/gitlab.rb`:
```ruby
redis_slave_role['enable'] = true
redis_sentinel_role['enable'] = true
redis['bind'] = '10.0.0.3'
redis['port'] = 6379
redis['password'] = 'redis-password-goes-here'
redis['master_password'] = 'redis-password-goes-here'
redis['master_ip'] = '10.0.0.1' # IP of master Redis server
#redis['master_port'] = 6379 # Port of master Redis server, uncomment to change to non default
redis['master_name'] = 'gitlab-redis' # must be the same in every sentinel node
sentinel['bind'] = '10.0.0.3'
# sentinel['port'] = 26379 # uncomment to change default port
sentinel['quorum'] = 2
# sentinel['down_after_milliseconds'] = 10000
# sentinel['failover_timeout'] = 60000
```
[Reconfigure Omnibus GitLab][reconfigure] for the changes to take effect.
### Example configuration for the GitLab application
In `/etc/gitlab/gitlab.rb`:
```ruby
redis['master_name'] = 'gitlab-redis'
redis['password'] = 'redis-password-goes-here'
gitlab_rails['redis_sentinels'] = [
{'host' => '10.0.0.1', 'port' => 26379},
{'host' => '10.0.0.2', 'port' => 26379},
{'host' => '10.0.0.3', 'port' => 26379}
]
```
[Reconfigure Omnibus GitLab][reconfigure] for the changes to take effect.
## Advanced configuration
Omnibus GitLab configures some things behind the curtains to make the sysadmins'
lives easier. If you want to know what happens underneath keep reading.
### Control running services
In the previous example, we've used `redis_sentinel_role` and
`redis_master_role` which simplifies the amount of configuration changes.
If you want more control, here is what each one sets for you automatically
when enabled:
```ruby
## Redis Sentinel Role
redis_sentinel_role['enable'] = true
# When Sentinel Role is enabled, the following services are also enabled
sentinel['enable'] = true
# The following services are disabled
redis['enable'] = false
bootstrap['enable'] = false
nginx['enable'] = false
postgresql['enable'] = false
gitlab_rails['enable'] = false
mailroom['enable'] = false
-------
## Redis master/slave Role
redis_master_role['enable'] = true # enable only one of them
redis_slave_role['enable'] = true # enable only one of them
# When Redis Master or Slave role are enabled, the following services are
# enabled/disabled. Note that if Redis and Sentinel roles are combined, both
# services will be enabled.
# The following services are disabled
sentinel['enable'] = false
bootstrap['enable'] = false
nginx['enable'] = false
postgresql['enable'] = false
gitlab_rails['enable'] = false
mailroom['enable'] = false
# For Redis Slave role, also change this setting from default 'true' to 'false':
redis['master'] = false
```
```yaml
# resque.yaml
production:
url: redis://my-primary-redis:6378
sentinels:
-
host: slave1
port: 26380 # point to sentinel, not to redis port
-
host: slave2
port: 26381 # point to sentinel, not to redis port
You can find the relevant attributes defined in [gitlab_rails.rb][omnifile].
## Troubleshooting
There are a lot of moving parts that needs to be taken care carefully
in order for the HA setup to work as expected.
Before proceeding with the troubleshooting below, check your firewall rules:
- Redis machines
- Accept TCP connection in `6379`
- Connect to the other Redis machines via TCP in `6379`
- Sentinel machines
- Accept TCP connection in `26379`
- Connect to other Sentinel machines via TCP in `26379`
- Connect to the Redis machines via TCP in `6379`
### Troubleshooting Redis replication
You can check if everything is correct by connecting to each server using
`redis-cli` application, and sending the `INFO` command.
If authentication was correctly defined, it should fail with:
`NOAUTH Authentication required` error. Try to authenticate with the
previous defined password with `AUTH redis-password-goes-here` and
try the `INFO` command again.
Look for the `# Replication` section where you should see some important
information like the `role` of the server.
When connected to a `master` redis, you will see the number of connected
`slaves`, and a list of each with connection details:
```
# Replication
role:master
connected_slaves:1
slave0:ip=10.133.5.21,port=6379,state=online,offset=208037514,lag=1
master_repl_offset:208037658
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:206989083
repl_backlog_histlen:1048576
```
When in doubt, please read [Redis Sentinel documentation](http://redis.io/topics/sentinel)
When it's a `slave`, you will see details of the master connection and if
its `up` or `down`:
```
# Replication
role:slave
master_host:10.133.1.58
master_port:6379
master_link_status:up
master_last_io_seconds_ago:1
master_sync_in_progress:0
slave_repl_offset:208096498
slave_priority:100
slave_read_only:1
connected_slaves:0
master_repl_offset:0
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0
```
### Troubleshooting Sentinel
If you get an error like: `Redis::CannotConnectError: No sentinels available.`,
there may be something wrong with your configuration files or it can be related
to [this issue][gh-531].
You must make sure you are defining the same value in `redis['master_name']`
and `redis['master_pasword']` as you defined for your sentinel node.
The way the redis connector `redis-rb` works with sentinel is a bit
non-intuitive. We try to hide the complexity in omnibus, but it still requires
a few extra configs.
---
......@@ -273,7 +788,7 @@ To make sure your configuration is correct:
sudo gitlab-rails console
# For source installations
sudo -u git rails console RAILS_ENV=production
sudo -u git rails console production
```
1. Run in the console:
......@@ -288,8 +803,8 @@ To make sure your configuration is correct:
1. To simulate a failover on master Redis, SSH into the Redis server and run:
```bash
# port must match your master redis port
redis-cli -h localhost -p 6379 DEBUG sleep 60
# port must match your master redis port, and the sleep time must be a few seconds bigger than defined one
redis-cli -h localhost -p 6379 DEBUG sleep 20
```
1. Then back in the Rails console from the first step, run:
......@@ -301,10 +816,26 @@ To make sure your configuration is correct:
You should see a different port after a few seconds delay
(the failover/reconnect time).
---
Read more on high-availability configuration:
## Changelog
Changes to Redis HA over time.
**8.14**
- Redis Sentinel support is production-ready and bundled in the Omnibus GitLab
Enterprise Edition package
- Documentation restructure for better readability
**8.11**
- Experimental Redis Sentinel support was added
## Further reading
Read more on High Availability:
1. [High Availability Overview](README.md)
1. [Configure the database](database.md)
1. [Configure NFS](nfs.md)
1. [Configure the GitLab application servers](gitlab.md)
......@@ -315,3 +846,10 @@ Read more on high-availability configuration:
[reconfigure]: ../restart_gitlab.md#omnibus-gitlab-reconfigure
[gh-531]: https://github.com/redis/redis-rb/issues/531
[gh-534]: https://github.com/redis/redis-rb/issues/534
[redis]: http://redis.io/
[sentinel]: http://redis.io/topics/sentinel
[omnifile]: https://gitlab.com/gitlab-org/omnibus-gitlab/blob/master/files/gitlab-cookbooks/gitlab/libraries/gitlab_rails.rb
[source]: ../../install/installation.md
[ce]: https://about.gitlab.com/downloads
[ee]: https://about.gitlab.com/downloads-ee
[it]: https://gitlab.com/gitlab-org/gitlab-ce/uploads/c4cc8cd353604bd80315f9384035ff9e/The_Internet_IT_Crowd.png
doc/administration/high_availability/redis_source.md 0 → 100644
View file @ da0906c3
# Configuring non-Omnibus Redis for GitLab HA
This is the documentation for configuring a Highly Available Redis setup when
you have installed Redis all by yourself and not using the bundled one that
comes with the Omnibus packages.
We cannot stress enough the importance of reading the
[Overview section](redis.md#overview) of the Omnibus Redis HA as it provides
some invaluable information to the configuration of Redis. Please proceed to
read it before going forward with this guide.
We also highly recommend that you use the Omnibus GitLab packages, as we
optimize them specifically for GitLab, and we will take care of upgrading Redis
to the latest supported version.
If you're not sure whether this guide is for you, please refer to
[Available configuration setups](redis.md#available-configuration-setups) in
the Omnibus Redis HA documentation.
## Configuring your own Redis server
This is the section where we install and setup the new Redis instances.
### Prerequisites
- All Redis servers in this guide must be configured to use a TCP connection
instead of a socket. To configure Redis to use TCP connections you need to
define both `bind` and `port` in the Redis config file. You can bind to all
interfaces (`0.0.0.0`) or specify the IP of the desired interface
(e.g., one from an internal network).
- Since Redis 3.2, you must define a password to receive external connections
(`requirepass`).
- If you are using Redis with Sentinel, you will also need to define the same
password for the slave password definition (`masterauth`) in the same instance.
In addition, read the prerequisites as described in the
[Omnibus Redis HA document](redis.md#prerequisites) since they provide some
valuable information for the general setup.
### Step 1. Configuring the master Redis instance
Assuming that the Redis master instance IP is `10.0.0.1`:
1. [Install Redis](../../install/installation.md#6-redis)
1. Edit `/etc/redis/redis.conf`:
```conf
## Define a `bind` address pointing to a local IP that your other machines
## can reach you. If you really need to bind to an external accessible IP, make
## sure you add extra firewall rules to prevent unauthorized access:
bind 10.0.0.1
## Define a `port` to force redis to listen on TCP so other machines can
## connect to it (default port is `6379`).
port 6379
## Set up password authentication (use the same password in all nodes).
## The password should be defined equal for both `requirepass` and `masterauth`
## when setting up Redis to use with Sentinel.
requirepass redis-password-goes-here
masterauth redis-password-goes-here
```
1. Restart the Redis service for the changes to take effect.
### Step 2. Configuring the slave Redis instances
Assuming that the Redis slave instance IP is `10.0.0.2`:
1. [Install Redis](../../install/installation.md#6-redis)
1. Edit `/etc/redis/redis.conf`:
```conf
## Define a `bind` address pointing to a local IP that your other machines
## can reach you. If you really need to bind to an external accessible IP, make
## sure you add extra firewall rules to prevent unauthorized access:
bind 10.0.0.2
## Define a `port` to force redis to listen on TCP so other machines can
## connect to it (default port is `6379`).
port 6379
## Set up password authentication (use the same password in all nodes).
## The password should be defined equal for both `requirepass` and `masterauth`
## when setting up Redis to use with Sentinel.
requirepass redis-password-goes-here
masterauth redis-password-goes-here
## Define `slaveof` pointing to the Redis master instance with IP and port.
slaveof 10.0.0.1 6379
```
1. Restart the Redis service for the changes to take effect.
1. Go through the steps again for all the other slave nodes.
### Step 3. Configuring the Redis Sentinel instances
Sentinel is a special type of Redis server. It inherits most of the basic
configuration options you can define in `redis.conf`, with specific ones
starting with `sentinel` prefix.
Assuming that the Redis Sentinel is installed on the same instance as Redis
master with IP `10.0.0.1` (some settings might overlap with the master):
1. [Install Redis Sentinel](http://redis.io/topics/sentinel)
1. Edit `/etc/redis/sentinel.conf`:
```conf
## Define a `bind` address pointing to a local IP that your other machines
## can reach you. If you really need to bind to an external accessible IP, make
## sure you add extra firewall rules to prevent unauthorized access:
bind 10.0.0.1
## Define a `port` to force Sentinel to listen on TCP so other machines can
## connect to it (default port is `6379`).
port 26379
## Set up password authentication (use the same password in all nodes).
## The password should be defined equal for both `requirepass` and `masterauth`
## when setting up Redis to use with Sentinel.
requirepass redis-password-goes-here
masterauth redis-password-goes-here
## Define with `sentinel auth-pass` the same shared password you have
## defined for both Redis master and slaves instances.
sentinel auth-pass gitlab-redis redis-password-goes-here
## Define with `sentinel monitor` the IP and port of the Redis
## master node, and the quorum required to start a failover.
sentinel monitor gitlab-redis 10.0.0.1 6379 2
## Define with `sentinel down-after-milliseconds` the time in `ms`
## that an unresponsive server will be considered down.
sentinel down-after-milliseconds gitlab-redis 10000
## Define a value for `sentinel failover_timeout` in `ms`. This has multiple
## meanings:
##
## * The time needed to re-start a failover after a previous failover was
## already tried against the same master by a given Sentinel, is two
## times the failover timeout.
##
## * The time needed for a slave replicating to a wrong master according
## to a Sentinel current configuration, to be forced to replicate
## with the right master, is exactly the failover timeout (counting since
## the moment a Sentinel detected the misconfiguration).
##
## * The time needed to cancel a failover that is already in progress but
## did not produced any configuration change (SLAVEOF NO ONE yet not
## acknowledged by the promoted slave).
##
## * The maximum time a failover in progress waits for all the slaves to be
## reconfigured as slaves of the new master. However even after this time
## the slaves will be reconfigured by the Sentinels anyway, but not with
## the exact parallel-syncs progression as specified.
sentinel failover_timeout 30000
```
1. Restart the Redis service for the changes to take effect.
1. Go through the steps again for all the other Sentinel nodes.
### Step 4. Configuring the GitLab application
You can enable or disable Sentinel support at any time in new or existing
installations. From the GitLab application perspective, all it requires is
the correct credentials for the Sentinel nodes.
While it doesn't require a list of all Sentinel nodes, in case of a failure,
it needs to access at least one of listed ones.
The following steps should be performed in the [GitLab application server](gitlab.md)
which ideally should not have Redis or Sentinels in the same machine for a HA
setup:
1. Edit `/home/git/gitlab/config/resque.yml` following the example in
[resque.yml.example][resque], and uncomment the Sentinel lines, pointing to
the correct server credentials:
```yaml
# resque.yaml
production:
url: redis://:redi-password-goes-here@gitlab-redis/
sentinels:
-
host: 10.0.0.1
port: 26379 # point to sentinel, not to redis port
-
host: 10.0.0.2
port: 26379 # point to sentinel, not to redis port
-
host: 10.0.0.3
port: 26379 # point to sentinel, not to redis port
```
1. [Restart GitLab][restart] for the changes to take effect.
## Example of minimal configuration with 1 master, 2 slaves and 3 Sentinels
In this example we consider that all servers have an internal network
interface with IPs in the `10.0.0.x` range, and that they can connect
to each other using these IPs.
In a real world usage, you would also setup firewall rules to prevent
unauthorized access from other machines, and block traffic from the
outside ([Internet][it]).
For this example, **Sentinel 1** will be configured in the same machine as the
**Redis Master**, **Sentinel 2** and **Sentinel 3** in the same machines as the
**Slave 1** and **Slave 2** respectively.
Here is a list and description of each **machine** and the assigned **IP**:
* `10.0.0.1`: Redis Master + Sentinel 1
* `10.0.0.2`: Redis Slave 1 + Sentinel 2
* `10.0.0.3`: Redis Slave 2 + Sentinel 3
* `10.0.0.4`: GitLab application
Please note that after the initial configuration, if a failover is initiated
by the Sentinel nodes, the Redis nodes will be reconfigured and the **Master**
will change permanently (including in `redis.conf`) from one node to the other,
until a new failover is initiated again.
The same thing will happen with `sentinel.conf` that will be overridden after the
initial execution, after any new sentinel node starts watching the **Master**,
or a failover promotes a different **Master** node.
### Example configuration for Redis master and Sentinel 1
1. In `/etc/redis/redis.conf`:
```conf
bind 10.0.0.1
port 6379
requirepass redis-password-goes-here
masterauth redis-password-goes-here
```
1. In `/etc/redis/sentinel.conf`:
```conf
bind 10.0.0.1
port 26379
sentinel auth-pass gitlab-redis redis-password-goes-here
sentinel monitor gitlab-redis 10.0.0.1 6379 2
sentinel down-after-milliseconds gitlab-redis 10000
sentinel failover_timeout 30000
```
1. Restart the Redis service for the changes to take effect.
### Example configuration for Redis slave 1 and Sentinel 2
1. In `/etc/redis/redis.conf`:
```conf
bind 10.0.0.2
port 6379
requirepass redis-password-goes-here
masterauth redis-password-goes-here
slaveof 10.0.0.1 6379
```
1. In `/etc/redis/sentinel.conf`:
```conf
bind 10.0.0.2
port 26379
sentinel auth-pass gitlab-redis redis-password-goes-here
sentinel monitor gitlab-redis 10.0.0.1 6379 2
sentinel down-after-milliseconds gitlab-redis 10000
sentinel failover_timeout 30000
```
1. Restart the Redis service for the changes to take effect.
### Example configuration for Redis slave 2 and Sentinel 3
1. In `/etc/redis/redis.conf`:
```conf
bind 10.0.0.3
port 6379
requirepass redis-password-goes-here
masterauth redis-password-goes-here
slaveof 10.0.0.1 6379
```
1. In `/etc/redis/sentinel.conf`:
```conf
bind 10.0.0.3
port 26379
sentinel auth-pass gitlab-redis redis-password-goes-here
sentinel monitor gitlab-redis 10.0.0.1 6379 2
sentinel down-after-milliseconds gitlab-redis 10000
sentinel failover_timeout 30000
```
1. Restart the Redis service for the changes to take effect.
### Example configuration of the GitLab application
1. Edit `/home/git/gitlab/config/resque.yml`:
```yaml
production:
url: redis://:redi-password-goes-here@gitlab-redis/
sentinels:
-
host: 10.0.0.1
port: 26379 # point to sentinel, not to redis port
-
host: 10.0.0.2
port: 26379 # point to sentinel, not to redis port
-
host: 10.0.0.3
port: 26379 # point to sentinel, not to redis port
```
1. [Restart GitLab][restart] for the changes to take effect.
## Troubleshooting
We have a more detailed [Troubleshooting](redis.md#troubleshooting) explained
in the documentation for Omnibus GitLab installations. Here we will list only
the things that are specific to a source installation.
If you get an error in GitLab like `Redis::CannotConnectError: No sentinels available.`,
there may be something wrong with your configuration files or it can be related
to [this upstream issue][gh-531].
You must make sure that `resque.yml` and `sentinel.conf` are configured correctly,
otherwise `redis-rb` will not work properly.
The `master-group-name` ('gitlab-redis') defined in (`sentinel.conf`)
**must** be used as the hostname in GitLab (`resque.yml`):
```conf
# sentinel.conf:
sentinel monitor gitlab-redis 10.0.0.1 6379 2
sentinel down-after-milliseconds gitlab-redis 10000
sentinel config-epoch gitlab-redis 0
sentinel leader-epoch gitlab-redis 0
```
```yaml
# resque.yaml
production:
url: redis://:myredispassword@gitlab-redis/
sentinels:
-
host: 10.0.0.1
port: 26379 # point to sentinel, not to redis port
-
host: 10.0.0.2
port: 26379 # point to sentinel, not to redis port
-
host: 10.0.0.3
port: 26379 # point to sentinel, not to redis port
```
When in doubt, please read [Redis Sentinel documentation](http://redis.io/topics/sentinel).
[gh-531]: https://github.com/redis/redis-rb/issues/531
[downloads]: https://about.gitlab.com/downloads
[restart]: ../restart_gitlab.md#installations-from-source
[it]: https://gitlab.com/gitlab-org/gitlab-ce/uploads/c4cc8cd353604bd80315f9384035ff9e/The_Internet_IT_Crowd.png
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