Install the GitLab agent server for Kubernetes (KAS)

DETAILS: Tier: Free, Premium, Ultimate Offering: Self-managed

The agent server is a component installed together with GitLab. It is required to manage the GitLab agent for Kubernetes.

The KAS acronym refers to the former name, Kubernetes agent server.

The agent server for Kubernetes is installed and available on GitLab.com at wss://kas.gitlab.com. If you use self-managed GitLab, by default the agent server is installed and available.

Installation options

As a GitLab administrator, you can control the agent server installation:

For Linux package installations.
For GitLab Helm chart installations.

For Linux package installations

The agent server for Linux package installations can be enabled on a single node, or on multiple nodes at once. By default, the agent server is enabled and available at ws://gitlab.example.com/-/kubernetes-agent/.

Disable on a single node

To disable the agent server on a single node:

Edit /etc/gitlab/gitlab.rb:
```
gitlab_kas['enable'] = false
```
Reconfigure GitLab.

Configure KAS to listen on a UNIX socket

If you use GitLab behind a proxy, KAS might not work correctly. You can resolve this issue on a single-node installation, you can configure KAS to listen on a UNIX socket.

To configure KAS to listen on a UNIX socket:

Create a directory for the KAS sockets:

sudo mkdir -p /var/opt/gitlab/gitlab-kas/sockets/

Edit /etc/gitlab/gitlab.rb:

gitlab_kas['internal_api_listen_network'] = 'unix'
gitlab_kas['internal_api_listen_address'] = '/var/opt/gitlab/gitlab-kas/sockets/internal-api.socket'
gitlab_kas['private_api_listen_network'] = 'unix'
gitlab_kas['private_api_listen_address'] = '/var/opt/gitlab/gitlab-kas/sockets/private-api.socket'
gitlab_kas['env'] = {
  'SSL_CERT_DIR' => "/opt/gitlab/embedded/ssl/certs/",
  'OWN_PRIVATE_API_URL' => 'unix:///var/opt/gitlab/gitlab-kas/sockets/private-api.socket'
}

Reconfigure GitLab.

For additional configuration options, see the GitLab Kubernetes agent server section of gitlab.rb.template.

Enable on multiple nodes

To enable the agent server on multiple nodes:

For each agent server node, edit /etc/gitlab/gitlab.rb:

gitlab_kas_external_url 'wss://kas.gitlab.example.com/'

gitlab_kas['api_secret_key'] = '<32_bytes_long_base64_encoded_value>'
gitlab_kas['private_api_secret_key'] = '<32_bytes_long_base64_encoded_value>'
gitlab_kas['private_api_listen_address'] = '0.0.0.0:8155'
gitlab_kas['env'] = {
  'SSL_CERT_DIR' => "/opt/gitlab/embedded/ssl/certs/",
  'OWN_PRIVATE_API_URL' => 'grpc://<ip_or_hostname_of_this_host>:8155' # use grpcs:// when using TLS on the private API endpoint

  # 'OWN_PRIVATE_API_HOST' => '<server-name-from-cert>' # Add if you want to use TLS for KAS->KAS communication. This is used to verify the TLS certificate host name.

  # 'OWN_PRIVATE_API_CIDR' => '10.0.0.0/8', # IPv4 example
  # 'OWN_PRIVATE_API_CIDR' => '2001:db8:8a2e:370::7334/64', # IPv6 example
  # 'OWN_PRIVATE_API_PORT' => '8155',
  # 'OWN_PRIVATE_API_SCHEME' => 'grpc',
}

gitlab_rails['gitlab_kas_external_url'] = 'wss://gitlab.example.com/-/kubernetes-agent/'
gitlab_rails['gitlab_kas_internal_url'] = 'grpc://kas.internal.gitlab.example.com'
gitlab_rails['gitlab_kas_external_k8s_proxy_url'] = 'https://gitlab.example.com/-/kubernetes-agent/k8s-proxy/'

You might not be able to specify an exact IP address or host name in the OWN_PRIVATE_API_URL variable. For example, if the kas host is assigned an IP dynamically.

In this situation, you can configure OWN_PRIVATE_API_CIDR instead to set up kas to dynamically construct OWN_PRIVATE_API_URL:

Comment out OWN_PRIVATE_API_URL to disable this variable.
Configure OWN_PRIVATE_API_CIDR to specify what network kas listens on. When you start kas, kas looks at the IP addresses the host is assigned, and uses the address that matches the specified CIDR as its own private IP address.
By default, kas uses the port from the private_api_listen_address parameter. Configure OWN_PRIVATE_API_PORT to use a different port.
Optional. By default, kas uses the grpc scheme. If you use TLS on the private API endpoint, configure OWN_PRIVATE_API_SCHEME=grpcs.

Reconfigure GitLab.

Agent server node settings

Setting	Description
`gitlab_kas['private_api_listen_address']`	The address the agent server listens on. Set to `0.0.0.0` or to an IP address reachable by other nodes in the cluster.
`gitlab_kas['api_secret_key']`	The shared secret used for authentication between KAS and GitLab. The value must be Base64-encoded and exactly 32 bytes long.
`gitlab_kas['private_api_secret_key']`	The shared secret used for authentication between different KAS instances. The value must be Base64-encoded and exactly 32 bytes long.
`OWN_PRIVATE_API_URL`	The environment variable used by KAS for service discovery. Set to the hostname or IP address of the node you're configuring. The node must be reachable by other nodes in the cluster.
`OWN_PRIVATE_API_HOST`	Optional value used to verify the TLS certificate host name. ¹ A client compares this value to the host name in the server's TLS certificate file.
`gitlab_kas_external_url`	The user-facing URL for the in-cluster `agentk`. Can be a fully qualified domain or subdomain, ² or a GitLab external URL. ³ If blank, defaults to a GitLab external URL.
`gitlab_rails['gitlab_kas_external_url']`	The user-facing URL for the in-cluster `agentk`. If blank, defaults to the `gitlab_kas_external_url`.
`gitlab_rails['gitlab_kas_external_k8s_proxy_url']`	The user-facing URL for Kubernetes API proxying. If blank, defaults to a URL based on `gitlab_kas_external_url`.
`gitlab_rails['gitlab_kas_internal_url']`	The internal URL the GitLab backend uses to communicate with KAS.

Footnotes:

TLS for outbound connections is enabled when OWN_PRIVATE_API_URL or OWN_PRIVATE_API_SCHEME starts with grpcs.
For example, wss://kas.gitlab.example.com/.
For example, wss://gitlab.example.com/-/kubernetes-agent/.

For GitLab Helm Chart

See how to use the GitLab-KAS chart.

Kubernetes API proxy cookie

Introduced in GitLab 15.10 with feature flags named kas_user_access and kas_user_access_project. Disabled by default.

Feature flags kas_user_access and kas_user_access_project enabled in GitLab 16.1.

Feature flags kas_user_access and kas_user_access_project removed in GitLab 16.2.

KAS proxies Kubernetes API requests to the GitLab agent with either:

A CI/CD job.
GitLab user credentials.

To authenticate with user credentials, Rails sets a cookie for the GitLab frontend. This cookie is called _gitlab_kas and it contains an encrypted session ID, like the _gitlab_session cookie. The _gitlab_kas cookie must be sent to the KAS proxy endpoint with every request to authenticate and authorize the user.

Troubleshooting

If you have issues while using the agent server for Kubernetes, view the service logs by running the following command:

kubectl logs -f -l=app=kas -n <YOUR-GITLAB-NAMESPACE>

In Linux package installations, find the logs in /var/log/gitlab/gitlab-kas/.

You can also troubleshoot issues with individual agents.

Configuration file not found

If you get the following error message:

time="2020-10-29T04:44:14Z" level=warning msg="Config: failed to fetch" agent_id=2 error="configuration file not found: \".gitlab/agents/test-agent/config.yaml\

The path is incorrect for either:

The repository where the agent was registered.
The agent configuration file.

To fix this issue, ensure that the paths are correct.

`dial tcp <GITLAB_INTERNAL_IP>:443: connect: connection refused`

If you are running self-managed GitLab and:

The instance isn't running behind an SSL-terminating proxy.
The instance doesn't have HTTPS configured on the GitLab instance itself.
The instance's hostname resolves locally to its internal IP address.

When the agent server tries to connect to the GitLab API, the following error might occur:

{"level":"error","time":"2021-08-16T14:56:47.289Z","msg":"GetAgentInfo()","correlation_id":"01FD7QE35RXXXX8R47WZFBAXTN","grpc_service":"gitlab.agent.reverse_tunnel.rpc.ReverseTunnel","grpc_method":"Connect","error":"Get \"https://gitlab.example.com/api/v4/internal/kubernetes/agent_info\": dial tcp 172.17.0.4:443: connect: connection refused"}

To fix this issue for Linux package installations, set the following parameter in /etc/gitlab/gitlab.rb. Replace gitlab.example.com with your GitLab instance's hostname:

gitlab_kas['gitlab_address'] = 'http://gitlab.example.com'