87 lines
5.1 KiB
Markdown
87 lines
5.1 KiB
Markdown
---
|
|
stage: Configure
|
|
group: Configure
|
|
info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
|
|
---
|
|
|
|
# Kubernetes Agent development **(PREMIUM ONLY)**
|
|
|
|
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
|
|
[bidirectional streaming](https://grpc.io/docs/what-is-grpc/core-concepts/#bidirectional-streaming-rpc)
|
|
to allow the connection acceptor (the gRPC server, GitLab Kubernetes Agent Server) to
|
|
act as a client. The connection acceptor sends requests as gRPC replies. The client-server
|
|
relationship is inverted because the connection must be initiated from inside the
|
|
Kubernetes cluster to bypass any firewall or NAT the cluster may be located behind.
|
|
To learn more about this inversion, read
|
|
[issue #212810](https://gitlab.com/gitlab-org/gitlab/-/issues/212810).
|
|
|
|
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.
|
|
|
|
<i class="fa fa-youtube-play youtube" aria-hidden="true"></i>
|
|
To learn more about how the repository is structured, see
|
|
[GitLab Kubernetes Agent repository overview](https://www.youtube.com/watch?v=j8CyaCWroUY).
|
|
|
|
## Guiding principles
|
|
|
|
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).
|