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# Using a GitOps workflow for Kubernetes **(PREMIUM)**
> - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/259669) in GitLab 13.7.
> - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/332227) in GitLab 14.0, the `resource_inclusions` and `resource_exclusions` attributes were removed and `reconcile_timeout`, `dry_run_strategy`, `prune`, `prune_timeout`, `prune_propagation_policy`, and `inventory_policy` attributes were added.
- Resource management with [server-side applies](https://kubernetes.io/docs/reference/using-api/server-side-apply/) for transparent multi-actor field management.
This diagram shows the repositories and main actors in a GitOps deployment:
```mermaid
sequenceDiagram
participant D as Developer
participant A as Application code repository
participant M as Manifest repository
participant K as GitLab agent
participant C as Agent configuration repository
loop Regularly
K-->>C: Grab the configuration
end
D->>+A: Pushing code changes
A->>M: Updating manifest
loop Regularly
K-->>M: Watching changes
M-->>K: Pulling and applying changes
end
```
For details, view the [architecture documentation](https://gitlab.com/gitlab-org/cluster-integration/gitlab-agent/-/blob/master/doc/architecture.md#high-level-architecture).
## GitOps workflow steps
To update a Kubernetes cluster by using GitOps, complete the following steps.
1. Ensure you have a working Kubernetes cluster, and that the manifests are in a GitLab project.
1. In the same project, [register and install the GitLab agent](install/index.md).
1. Configure the agent configuration file so that the agent monitors the project for changes to the Kubernetes manifests.
Use the [GitOps configuration reference](#gitops-configuration-reference) for guidance.
Any time you commit updates to your Kubernetes manifests, the agent updates the cluster.
## GitOps configuration reference
The following snippet shows an example of the possible keys and values for the GitOps section of an agent configuration file.
```yaml
gitops:
manifest_projects:
- id: gitlab-org/cluster-integration/gitlab-agent
default_namespace: my-ns
paths:
# Read all YAML files from this directory.
- glob: '/team1/app1/*.yaml'
# Read all .yaml files from team2/apps and all subdirectories.
- glob: '/team2/apps/**/*.yaml'
# If 'paths' is not specified or is an empty list, the configuration below is used.
- glob: '/**/*.{yaml,yml,json}'
reconcile_timeout: 3600s
dry_run_strategy: none
prune: true
prune_timeout: 3600s
prune_propagation_policy: foreground
inventory_policy: must_match
```
| Keyword | Description |
|--|--|
| `manifest_projects` | Projects where your Kubernetes manifests are stored. The agent monitors the files in the repositories in these projects. When manifest files change, the agent deploys the changes to the cluster. |
| `id` | Required. Path to a Git repository that has Kubernetes manifests in YAML or JSON format. No authentication mechanisms are currently supported. |
| `default_namespace` | Namespace to use if not set explicitly in object manifest. Also used for inventory `ConfigMap` objects. |
| `paths` | Repository paths to scan for manifest files. Directories with names that start with a dot `(.)` are ignored. |
| `paths[].glob` | Required. See [doublestar](https://github.com/bmatcuk/doublestar#about) and [the match function](https://pkg.go.dev/github.com/bmatcuk/doublestar/v2#Match) for globbing rules. |
| `reconcile_timeout` | Determines whether the applier should wait until all applied resources have been reconciled, and if so, how long to wait. Default is 3600 seconds (1 hour). |
| `dry_run_strategy` | Determines whether changes [should be performed](https://github.com/kubernetes-sigs/cli-utils/blob/d6968048dcd80b1c7b55d9e4f31fc25f71c9b490/pkg/common/common.go#L68-L89). Can be: `none`, `client`, or `server`. Default is `none`.|
| `prune` | Determines whether pruning of previously applied objects should happen after apply. Default is `true`. |
| `prune_timeout` | Determines whether to wait for all resources to be fully deleted after pruning, and if so, how long to wait. Default is 3600 seconds (1 hour). |
| `prune_propagation_policy` | The deletion propagation policy that [should be used for pruning](https://github.com/kubernetes/apimachinery/blob/44113beed5d39f1b261a12ec398a356e02358307/pkg/apis/meta/v1/types.go#L456-L470). Can be: `orphan`, `background`, or `foreground`. Default is `foreground`. |
| `inventory_policy` | Determines whether an inventory object can take over objects that belong to another inventory object or don't belong to any inventory object. This is done by determining if the apply/prune operation can go through for a resource based on comparison of the `inventory-id` value in the package and the `owning-inventory` annotation (`config.k8s.io/owning-inventory`) [in the live object](https://github.com/kubernetes-sigs/cli-utils/blob/d6968048dcd80b1c7b55d9e4f31fc25f71c9b490/pkg/inventory/policy.go#L12-L66). Can be: `must_match`, `adopt_if_no_inventory`, or `adopt_all`. Default is `must_match`. |
The GitLab agent for Kubernetes has annotations you can use to:
- **Sort resources**: Apply or delete resources in a specific order.
- **Use apply-time mutation**: Dynamically substitute fields from one resource configuration to another.
The agent has [default sorting](https://github.com/kubernetes-sigs/cli-utils/blob/d7d63f4b62897f584ca9e02b6faf4d2f327a9b09/pkg/ordering/sort.go#L74),
but with annotations, you can fine-tune the order and apply time-value injection.
To provide the GitOps functionality, the GitLab agent for Kubernetes uses the [`cli-utils` library](https://github.com/kubernetes-sigs/cli-utils/),
a Kubernetes SIG project. You can read more about the available annotations in the [`cli-utils` documentation](https://github.com/kubernetes-sigs/cli-utils/blob/master/README.md#apply-sort-ordering).
- [Learn more about apply sort ordering](https://github.com/kubernetes-sigs/cli-utils#apply-sort-ordering).
- [Learn more about apply-time mutation](https://github.com/kubernetes-sigs/cli-utils#apply-time-mutation).
## Automatic drift remediation
Drift happens when the current configuration of an infrastructure resource differs from its expected configuration.
Typically, this is caused by manually editing resources directly through the service that created the resource. Minimizing the
risk of drift helps to ensure configuration consistency and successful operations.
In GitLab, the agent for Kubernetes regularly compares the expected state from the `git` repository with
the known state from the `cluster`. Deviations from the `git` state are fixed at every check. These checks
happen automatically every 5 minutes. They are not configurable.
The agent uses [server-side applies](https://kubernetes.io/docs/reference/using-api/server-side-apply/).
As a result, every field in a resource can have different managers. Only fields managed by `git`
are checked for drift. This facilitates the use of in-cluster controllers to modify resources like
[Horizontal Pod Autoscalers](https://kubernetes.io/docs/tasks/run-application/horizontal-pod-autoscale/).
The following documentation and examples can help you get started with a GitOps workflow.
- [Managing Kubernetes secrets in a GitOps workflow](gitops/secrets_management.md)
- [Application and manifest repository example](https://gitlab.com/gitlab-examples/ops/gitops-demo/hello-world-service-gitops)
## Troubleshooting
### Avoiding conflicts when you have multiple projects
The agent watches each glob pattern set under a project's `paths` section independently, and makes updates to the cluster concurrently.
If changes are found at multiple paths, when the agent attempts to update the cluster,
a conflict can occur.
To prevent this from happening, consider storing a logical group of manifests in a single place and reference them only once to avoid overlapping globs.
For example, both of these globs match `*.yaml` files in the root directory
and could cause conflicts:
```yaml
gitops:
manifest_projects:
- id: project1
paths:
- glob: '/**/*.yaml'
- glob: '/*.yaml'
```
Instead, specify a single glob that matches all `*.yaml` files recursively:
```yaml
gitops:
manifest_projects:
- id: project1
paths:
- glob: '/**/*.yaml'
```
### Use multiple agents or projects
If you store your Kubernetes manifests in separate GitLab projects,
update your agent configuration file with the location of these projects.
WARNING:
The project with the agent's
configuration file can be private or public. Other projects with Kubernetes manifests must be public. Support for private manifest projects is tracked
in [this issue](https://gitlab.com/gitlab-org/gitlab/-/issues/283885).
