Connect existing clusters through cluster certificates (deprecated)

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Deprecated in GitLab 14.5.

WARNING: This feature was deprecated in GitLab 14.5. To connect your cluster to GitLab, use the GitLab agent instead.

If you have an existing Kubernetes cluster, you can add it to a project, group, or instance and benefit from the integration with GitLab.

Prerequisites

See the prerequisites below to add existing clusters to GitLab.

All clusters

To add any cluster to GitLab, you need:

Either a GitLab.com account or an account for a self-managed installation
The Maintainer role for group-level and project-level clusters.
Access to the Admin area for instance-level clusters.
A Kubernetes cluster.
Cluster administration access to the cluster with kubectl.

You can host your cluster in EKS, GKE, on premises, and with other providers. To host them on premises and with other providers, use either the EKS or GKE method to guide you through and enter your cluster's settings manually.

WARNING: GitLab doesn't support arm64 clusters. See the issue Helm Tiller fails to install on arm64 cluster for details.

EKS clusters

To add an existing EKS cluster, you need:

An Amazon EKS cluster with worker nodes properly configured.
kubectl installed and configured for access to the EKS cluster.
Ensure the token of the account has administrator privileges for the cluster.

GKE clusters

To add an existing GKE cluster, you need:

The container.clusterRoleBindings.create permission to create a cluster role binding. You can follow the Google Cloud documentation to grant access.

How to add an existing cluster

To add a Kubernetes cluster to your project, group, or instance:

Go to your:
1. Project's {cloud-gear} Operate > Kubernetes clusters page, for a project-level cluster.
2. Group's {cloud-gear} Kubernetes page, for a group-level cluster.
3. The Admin area's Kubernetes page, for an instance-level cluster.
On the Kubernetes clusters page, select the Connect with a certificate option from the Actions dropdown list.
On the Connect a cluster page, fill in the details:
1. Kubernetes cluster name (required) - The name you wish to give the cluster.
2. Environment scope (required) - The associated environment to this cluster.
3. API URL (required) - It's the URL that GitLab uses to access the Kubernetes API. Kubernetes exposes several APIs, we want the "base" URL that is common to all of them. For example, https://kubernetes.example.com rather than https://kubernetes.example.com/api/v1.
  
  Get the API URL by running this command:
```
kubectl cluster-info | grep -E 'Kubernetes master|Kubernetes control plane' | awk '/http/ {print $NF}'
```
4. CA certificate (required) - A valid Kubernetes certificate is needed to authenticate to the cluster. We use the certificate created by default.
  1. List the secrets with kubectl get secrets, and one should be named similar to default-token-xxxxx. Copy that token name for use below.
  2. Get the certificate by running this command:
```
kubectl get secret <secret name> -o jsonpath="{['data']['ca\.crt']}" | base64 --decode
```
    If the command returns the entire certificate chain, you must copy the Root CA certificate and any intermediate certificates at the bottom of the chain. A chain file has following structure:
```
   -----BEGIN MY CERTIFICATE-----
   -----END MY CERTIFICATE-----
   -----BEGIN INTERMEDIATE CERTIFICATE-----
   -----END INTERMEDIATE CERTIFICATE-----
   -----BEGIN INTERMEDIATE CERTIFICATE-----
   -----END INTERMEDIATE CERTIFICATE-----
   -----BEGIN ROOT CERTIFICATE-----
   -----END ROOT CERTIFICATE-----
```
5. Token - GitLab authenticates against Kubernetes using service tokens, which are scoped to a particular namespace. The token used should belong to a service account with cluster-admin privileges. To create this service account:
  1. Create a file called gitlab-admin-service-account.yaml with contents:
```
apiVersion: v1
kind: ServiceAccount
metadata:
  name: gitlab
  namespace: kube-system
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: gitlab-admin
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: cluster-admin
subjects:
  - kind: ServiceAccount
    name: gitlab
    namespace: kube-system
```
  2. Apply the service account and cluster role binding to your cluster:
```
kubectl apply -f gitlab-admin-service-account.yaml
```
    You need the container.clusterRoleBindings.create permission to create cluster-level roles. If you do not have this permission, you can alternatively enable Basic Authentication and then run the kubectl apply command as an administrator:
```
kubectl apply -f gitlab-admin-service-account.yaml --username=admin --password=<password>
```
    NOTE: Basic Authentication can be turned on and the password credentials can be obtained using the Google Cloud Console.
    
    Output:
```
serviceaccount "gitlab" created
clusterrolebinding "gitlab-admin" created
```
  3. Retrieve the token for the gitlab service account:
```
kubectl -n kube-system describe secret $(kubectl -n kube-system get secret | grep gitlab | awk '{print $1}')
```
    Copy the <authentication_token> value from the output:
```
Name:         gitlab-token-b5zv4
Namespace:    kube-system
Labels:       <none>
Annotations:  kubernetes.io/service-account.name=gitlab
             kubernetes.io/service-account.uid=bcfe66ac-39be-11e8-97e8-026dce96b6e8

Type:  kubernetes.io/service-account-token

Data
====
ca.crt:     1025 bytes
namespace:  11 bytes
token:      <authentication_token>
```
6. GitLab-managed cluster - Leave this checked if you want GitLab to manage namespaces and service accounts for this cluster. See the Managed clusters section for more information.
7. Project namespace (optional) - You don't have to fill this in. By leaving it blank, GitLab creates one for you. Also:
  - Each project should have a unique namespace.
  - The project namespace is not necessarily the namespace of the secret, if you're using a secret with broader permissions, like the secret from default.
  - You should not use default as the project namespace.
  - If you or someone created a secret specifically for the project, usually with limited permissions, the secret's namespace and project namespace may be the same.
Select the Add Kubernetes cluster button.

After about 10 minutes, your cluster is ready.

Disable Role-Based Access Control (RBAC) (optional)

When connecting a cluster via GitLab integration, you may specify whether the cluster is RBAC-enabled or not. This affects how GitLab interacts with the cluster for certain operations. If you did not check the RBAC-enabled cluster checkbox at creation time, GitLab assumes RBAC is disabled for your cluster when interacting with it. If so, you must disable RBAC on your cluster for the integration to work properly.

WARNING: Disabling RBAC means that any application running in the cluster, or user who can authenticate to the cluster, has full API access. This is a security concern, and may not be desirable.

To effectively disable RBAC, global permissions can be applied granting full access:

kubectl create clusterrolebinding permissive-binding \
  --clusterrole=cluster-admin \
  --user=admin \
  --user=kubelet \
  --group=system:serviceaccounts

Troubleshooting

CA certificate and token errors during authentication

If you encounter this error while connecting a Kubernetes cluster:

There was a problem authenticating with your cluster.
Please ensure your CA Certificate and Token are valid

Ensure you're properly pasting the service token. Some shells may add a line break to the service token, making it invalid. Ensure that there are no line breaks by pasting your token into an editor and removing any additional spaces.

You may also experience this error if your certificate is not valid. To check that your certificate's subject alternative names contain the correct domain for your cluster's API, run this command:

echo | openssl s_client -showcerts -connect kubernetes.example.com:443 -servername kubernetes.example.com 2>/dev/null |
openssl x509 -inform pem -noout -text

The -connect argument expects a host:port combination. For example, https://kubernetes.example.com would be kubernetes.example.com:443. The -servername argument expects a domain without any URI, for example kubernetes.example.com.