Add documentation for the network policy deployment via auto deploy

These changes also cover Cilium network plugin installation process

doc/topics/autodevops/index.md

@@ -713,6 +713,56 @@ workers:
     terminationGracePeriodSeconds: 60
 ```
 
+#### Network Policy
+
+> [Introduced](https://gitlab.com/gitlab-org/charts/auto-deploy-app/merge_requests/30) in GitLab 12.7.
+
+By default, all Kubernetes pods are
+[non-isolated](https://kubernetes.io/docs/concepts/services-networking/network-policies/#isolated-and-non-isolated-pods)
+and accept traffic from any source. You can use
+[NetworkPolicy](https://kubernetes.io/docs/concepts/services-networking/network-policies/)
+to restrict connections to selected pods or namespaces.
+
+NOTE: **Note:**
+You must use a Kubernetes network plugin that implements support for
+`NetworkPolicy`, the default network plugin for Kubernetes (`kubenet`)
+[doesn't implement](https://kubernetes.io/docs/concepts/extend-kubernetes/compute-storage-net/network-plugins/#kubenet)
+support for it. The [Cilium](https://cilium.io/) network plugin can be
+installed as a [cluster application](../../user/clusters/applications.md#install-cilium-using-gitlab-ci)
+to enable support for network policies.
+
+You can enable deployment of a network policy by setting the following
+in the `.gitlab/auto-deploy-values.yaml` file:
+
+```yml
+networkPolicy:
+  enabled: true
+```
+
+The default policy deployed by the auto deploy pipeline will allow
+traffic within a local namespace and from the `gitlab-managed-apps`
+namespace, all other inbound connection will be blocked. Outbound
+traffic is not affected by the default policy.
+
+You can also provide a custom [policy specification](https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.16/#networkpolicyspec-v1-networking-k8s-io)
+via the `.gitlab/auto-deploy-values.yaml` file, for example:
+
+```yml
+networkPolicy:
+  enabled: true
+  spec:
+    podSelector:
+      matchLabels:
+        app.gitlab.com/env: staging
+    ingress:
+    - from:
+      - podSelector:
+          matchLabels: {}
+      - namespaceSelector:
+          matchLabels:
+            app.gitlab.com/managed_by: gitlab
+```
+
 #### Running commands in the container
 
 Applications built with [Auto Build](#auto-build) using Herokuish, the default

doc/user/clusters/applications.md

@@ -477,6 +477,7 @@ Supported applications:
 - [cert-manager](#install-cert-manager-using-gitlab-ci)
 - [Sentry](#install-sentry-using-gitlab-ci)
 - [GitLab Runner](#install-gitlab-runner-using-gitlab-ci)
+- [Cilium](#install-cilium-using-gitlab-ci)
 
 ### Usage
 
@@ -661,6 +662,65 @@ management project. Refer to the
 [chart](https://gitlab.com/gitlab-org/charts/gitlab-runner) for the
 available configuration options.
 
+### Install Cilium using GitLab CI
+
+> [Introduced](https://gitlab.com/gitlab-org/cluster-integration/cluster-applications/merge_requests/22) in GitLab 12.7.
+
+[Cilium](https://cilium.io/) is a networking plugin for Kubernetes
+that you can use to implement support for
+[NetworkPolicy](https://kubernetes.io/docs/concepts/services-networking/network-policies/)
+resources.
+
+Enable Cilium in the `.gitlab/managed-apps/config.yaml` file to install it:
+
+```yaml
+# possible values are gke, eks or you can leave it blank
+clusterType: gke
+
+cilium:
+  installed: true
+```
+
+The `clusterType` variable enables the recommended Helm variables for
+a corresponding cluster type, the default value is blank. You can
+check the recommended variables for each cluster type in the official
+documentation:
+
+- [Google GKE](https://cilium.readthedocs.io/en/stable/gettingstarted/k8s-install-gke/#prepare-deploy-cilium)
+- [AWS EKS](https://cilium.readthedocs.io/en/stable/gettingstarted/k8s-install-eks/#prepare-deploy-cilium)
+
+You can customize Cilium's Helm variables by defining the
+`.gitlab/managed-apps/cilium/values.yaml` file in your cluster
+management project. Refer to the
+[Cilium chart](https://github.com/cilium/cilium/tree/master/install/kubernetes/cilium)
+for the available configuration options.
+
+CAUTION: **Caution:**
+Installation and removal of the Cilium [requires restart](https://cilium.readthedocs.io/en/stable/gettingstarted/k8s-install-gke/#restart-remaining-pods)
+of all affected pods in all namespaces to ensure that they are
+[managed](https://cilium.readthedocs.io/en/stable/troubleshooting/#ensure-pod-is-managed-by-cilium)
+by the correct networking plugin.
+
+NOTE: **Note:**
+Major upgrades might require additional setup steps, please consult
+the official [upgrade guide](https://docs.cilium.io/en/stable/install/upgrade/) for more
+information.
+
+By default, the drop log for traffic is logged out by the
+`cilium-monitor` sidecar container. You can check these logs via:
+
+```bash
+kubectl -n gitlab-managed-apps logs cilium-XXXX cilium-monitor
+```
+
+Drop logging can be disabled via `.gitlab/managed-apps/cilium/values.yaml`:
+
+```yml
+agent:
+  monitor:
+    enabled: false
+```
+
 ## Upgrading applications
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab-foss/merge_requests/24789) in GitLab 11.8.