Add Elastic Stack documentation

Add Elastic Stack documentationn

doc/user/clusters/applications.md

@@ -41,6 +41,7 @@ The following applications can be installed:
 - [JupyterHub](#jupyterhub)
 - [Knative](#knative)
 - [Crossplane](#crossplane)
+- [Elastic Stack](#elastic-stack)
 
 With the exception of Knative, the applications will be installed in a dedicated
 namespace called `gitlab-managed-apps`.
@@ -431,6 +432,38 @@ administrator to run following command within a Rails console:
 Feature.enable(:enable_cluster_application_crossplane)
 ```
 
+### Elastic Stack
+
+> Introduced in GitLab 12.7 for project- and group-level clusters.
+
+[Elastic Stack](https://www.elastic.co/products/elastic-stack) is a complete end-to-end
+log analysis solution which helps in deep searching, analyzing and visualizing the logs
+generated from different machines.
+
+GitLab is able to gather logs from pods in your cluster automatically.
+Filebeat will run as a DaemonSet on each node in your cluster, and it will ship container logs to Elasticsearch for querying.
+GitLab will then connect to Elasticsearch for logs instead of the Kubernetes API,
+and you will have access to more advanced querying capabilities.
+
+This is a preliminary release of Elastic Stack as a GitLab-managed application. By default,
+the ability to install it is disabled.
+
+To allow installation of Elastic Stack as a GitLab-managed application, ask a GitLab
+administrator to run following command within a Rails console:
+
+```ruby
+Feature.enable(:enable_cluster_application_elastic_stack)
+```
+
+Once the feature flag is set, to enable log shipping, install Elastic Stack into the cluster with the
+**Install** button.
+
+NOTE: **Note:**
+The [`stable/elastic-stack`](https://github.com/helm/charts/tree/master/stable/elastic-stack)
+chart is used to install this application with a
+[`values.yaml`](https://gitlab.com/gitlab-org/gitlab/blob/master/vendor/elastic_stack/values.yaml)
+file.
+
 ## Install using GitLab CI (alpha)
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab/merge_requests/20822) in GitLab 12.6.
@@ -639,6 +672,7 @@ The applications below can be uninstalled.
 | Knative  | 12.1+         | The associated IP will be deleted and cannot be restored. |
 | Prometheus  | 11.11+         | All data will be deleted and cannot be restored. |
 | Crossplane  | 12.5+         | All data will be deleted and cannot be restored. |
+| Elastic Stack  | 12.7+         | All data will be deleted and cannot be restored. |
 | Sentry  | 12.6+         | The PostgreSQL persistent volume will remain and should be manually removed for complete uninstall.  |
 
 To uninstall an application:

doc/user/project/clusters/kubernetes_pod_logs.md

@@ -41,9 +41,37 @@ Logs can be displayed by clicking on a specific pod from [Deploy Boards](../depl
 1. On the **Environments** page, you should see the status of the environment's pods with [Deploy Boards](../deploy_boards.md).
 1. When mousing over the list of pods, a tooltip will appear with the exact pod name and status.
    ![Deploy Boards pod list](img/pod_logs_deploy_board.png)
-1. Click on the desired pod to bring up the logs view, which will contain the last 500 lines for that pod.
-   You may switch between the following in this view:
-   - Pods.
-   - [From GitLab 12.4](https://gitlab.com/gitlab-org/gitlab/issues/5769), environments.
+1. Click on the desired pod to bring up the logs view.
 
-   Support for pods with multiple containers is coming [in a future release](https://gitlab.com/gitlab-org/gitlab/issues/6502).
+### Logs view
+
+The logs view will contain the last 500 lines for a pod, and has control to filter via:
+
+- Pods.
+- [From GitLab 12.4](https://gitlab.com/gitlab-org/gitlab/issues/5769), environments.
+- [From GitLab 12.7](https://gitlab.com/gitlab-org/gitlab/merge_requests/21656), [full text search](#full-text-search).
+
+Support for pods with multiple containers is coming [in a future release](https://gitlab.com/gitlab-org/gitlab/issues/13404).
+
+Support for historical data is coming [in a future release](https://gitlab.com/gitlab-org/gitlab/issues/196191).
+
+### Full text search
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/merge_requests/21656) in GitLab 12.7.
+
+When you enable [Elastic Stack](../../clusters/applications.md#elastic-stack) on your cluster,
+you can search the content of your logs via a search bar.
+
+The search is passed on to Elasticsearch using the [simple_query_string](https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-simple-query-string-query.html)
+Elasticsearch function, which supports the following operators:
+
+```
++ signifies AND operation
+| signifies OR operation
+- negates a single token
+" wraps a number of tokens to signify a phrase for searching
+* at the end of a term signifies a prefix query
+( and ) signify precedence
+~N after a word signifies edit distance (fuzziness)
+~N after a phrase signifies slop amount
+```