# High Availability

GitLab supports several different types of clustering and high-availability.
The solution you choose will be based on the level of scalability and
availability you require. The easiest solutions are scalable, but not necessarily
highly available.

## Architecture

There are two kinds of setups:

- active/active
- active/passive

### Active/Active

This architecture scales easily because all application servers handle
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.

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)
