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This page contains developer-specific information about the GitLab Kubernetes Agent.
[End-user documentation about the GitLab Kubernetes Agent](../../user/clusters/agent/index.md)
is also available.
The agent can help you perform tasks like these:
- Integrate a cluster, located behind a firewall or NAT, with GitLab. To
learn more, read [issue #212810, Invert the model GitLab.com uses for Kubernetes integration by leveraging long lived reverse tunnels](https://gitlab.com/gitlab-org/gitlab/-/issues/212810).
- Access API endpoints in a cluster in real time. For an example use case, read
[issue #218220, Allow Prometheus in K8s cluster to be installed manually](https://gitlab.com/gitlab-org/gitlab/-/issues/218220#note_348729266).
- Enable real-time features by pushing information about events happening in a cluster.
For example, you could build a cluster view dashboard to visualize changes in progress
in a cluster. For more information about these efforts, read about the
[Real-Time Working Group](https://about.gitlab.com/company/team/structure/working-groups/real-time/).
- Enable a [cache of Kubernetes objects through informers](https://github.com/kubernetes/client-go/blob/ccd5becdffb7fd8006e31341baaaacd14db2dcb7/tools/cache/shared_informer.go#L34-L183),
kept up-to-date with very low latency. This cache helps you:
- Reduce or eliminate information propagation latency by avoiding Kubernetes API calls
and polling, and only fetching data from an up-to-date cache.
- Lower the load placed on the Kubernetes API by removing polling.
- Eliminate any rate-limiting errors by removing polling.
- Simplify backend code by replacing polling code with cache access. While it's another
API call, no polling is needed. This example describes [fetching cached data synchronously from the front end](https://gitlab.com/gitlab-org/gitlab/-/issues/217792#note_348582537) instead of fetching data from the Kubernetes API.
## Architecture of the Kubernetes Agent
The GitLab Kubernetes Agent and the GitLab Kubernetes Agent Server use
This diagram describes how GitLab (`GitLab RoR`), the GitLab Kubernetes Agent (`agentk`), and the GitLab Kubernetes Agent Server (`kas`) work together.
```mermaid
graph TB
agentk -- gRPC bidirectional streaming --> kas
subgraph "GitLab"
kas[kas]
GitLabRoR[GitLab RoR] -- gRPC --> kas
kas -- gRPC --> Gitaly[Gitaly]
kas -- REST API --> GitLabRoR
end
subgraph "Kubernetes cluster"
agentk[agentk]
end
```
-`GitLab RoR` is the main GitLab application. It uses gRPC to talk to `kas`.
-`agentk` is the GitLab Kubernetes Agent. It keeps a connection established to a
`kas` instance, waiting for requests to process. It may also actively send information
about things happening in the cluster.
-`kas` is the GitLab Kubernetes Agent Server, and is responsible for:
- Accepting requests from `agentk`.
- [Authentication of requests](https://gitlab.com/gitlab-org/cluster-integration/gitlab-agent/-/blob/master/doc/identity_and_auth.md) from `agentk` by querying `GitLab RoR`.
- Fetching agent's configuration from a corresponding Git repository by querying Gitaly.
- Matching incoming requests from `GitLab RoR` with existing connections from
the right `agentk`, forwarding requests to it and forwarding responses back.
- (Optional) Sending notifications through ActionCable for events received from `agentk`.
- Polling manifest repositories for [GitOps support](https://gitlab.com/gitlab-org/cluster-integration/gitlab-agent/-/blob/master/doc/gitops.md) by communicating with Gitaly.
GitLab prefers to add logic into `kas` rather than `agentk`. `agentk` should be kept
streamlined and small to minimize the need for upgrades. On GitLab.com, `kas` is
managed by GitLab, so upgrades and features can be added without requiring you
to upgrade `agentk` in your clusters.
`agentk` can't be viewed as a dumb reverse proxy because features are planned to be built
[on top of the cache with informers](https://github.com/kubernetes/client-go/blob/ccd5becdffb7fd8006e31341baaaacd14db2dcb7/tools/cache/shared_informer.go#L34-L183).
