Guest post originally published on Flux’ blog by Daniel Holbach

tl;dr: Server-side reconciliation will make Flux more performant, improve overall observability and going forward will allow us to add new capabilities, like being able to preview local changes to manifests without pushing to upstream.

⚠ Changes required: Due to a Kubernetes issue, we require a certain set of Kubernetes releases (starting 1.16.11 – more on this below) as a minimum. The logs, events and alerts that report Kubernetes namespaced object changes are now using the Kind/Namespace/Name format instead of Kind/Name.


We rarely do this, but this time we want to give you some advance notice of a big upcoming feature you will be pleased about. Since Kubernetes moved server-side apply to GA, we are offering you a new reconciler based on it, and graduating the API to v1beta2.

What’s happening

Here is what you get

This is what you need to do to prepare

Check the Kubernetes version you are running in your cluster. All the versions below fix a regression in the managed fields and field type.

Kubernetes versionMinimum required
v1.16>= 1.16.11
v1.17>= 1.17.7
v1.18>= 1.18.4
v1.19 and later>= 1.19.0

Namespaced objects must contain metadata.namespace, defaulting to the default namespace is no longer supported. This means you will need to chase down any namespaced resources in your configuration files that are left to default, and give them a namespace. Keep in mind that kustomizations are often used to assign a namespace, so even if a particular file doesn’t have a namespace in it, it may not represent a problem.

The logs, events and alerts that report Kubernetes namespaced object changes are now using the Kind/Namespace/Name format instead of Kind/Name e.g.:

Service/flux-demo/podinfo unchanged
Deployment/flux-demo/podinfo configured
HorizontalPodAutoscaler/flux-demo/podinfo deleted

Any automation or monitoring that relies on a particular format in the logs will need to be adapted. Ideally, you should try to handle both the old and new formats.

In terms of API changes, the kustomize.toolkit.fluxcd.io/v1beta2 API is backwards compatible with v1beta1. This is done automatically by the Kubernetes API server, and no preparation is required. You may wish to translate your Flux Kustomization resources, though, according to the following table.

Additions, deprecations and removals:

Change in the new versionWhat you should do
Version is now v1beta2Change the version: apiVersion: kustomize.toolkit.fluxcd.io/v1beta2
.spec.validation removedServer-side validation is now assumed. Remove this field from .spec.
.spec.patchesStrategicMerge deprecated in favour of .spec.patchesConvert each entry from .spec.patchesStrategicMerge into an inline strategic merge patch, like this example given in the Kustomize documentation, and append to .spec.patches.. Note that the value in the patch field is quoted; that is, it is the YAML or JSON of the patch, stringified.
.spec.patchesJson6902 deprecated in favour of .spec.patchesConvert each entry from .spec.patchesJson6902 into an inline JSON6902 patch, and append to .spec.patches. Note that the value in the patch field is quoted; that is, it is the YAML or JSON of the patch, stringified.
.status.snapshot replaced by .status.inventory.status is not kept in files, so you will not need to account for this.
.spec.wait addedWhen true, the controller will wait for all the reconciled resources to become ready, and ignore .spec.healthChecks. There is no preparation needed for this, since it’s a new feature.

Why we are doing this

When we started Flux v2, we set a goal to stop relying on third party binaries for core features. While we have successfully replaced the Git CLI shell execs with Go libraries (go-git, git2go) and C libraries (libgit2, libssh2), the kustomize CLI with Go libraries (kustomize/api, kustomize/kyaml), we still depend on the kubectl CLI for the three-way-merge apply feature. With Kubernetes “server-side apply” being promoted to GA, we can finally get rid of kubectl and drive the reconciliation using exclusively the controller-runtime Go client.

Please take a look at the PR introducing this change, as it talks at length about the issues which are solved by this.

Sneak-preview and leaving feedback

If you would like a sneak-preview of the feature before it gets released and try out the v1beta2 API on your own test cluster, please follow the following steps:

  1. Install the latest Flux controllersflux install
  2. Apply the CRDs from this branchkubectl apply -k https://github.com/fluxcd/kustomize-controller/config/crd?ref=v1beta2
  3. Deploy the kustomize-controller build of this branchkubectl -n flux-system set image deployment/kustomize-controller \ manager=ghcr.io/fluxcd/kustomize-controller:v1beta2-8426b396

Please comment on this PR and let us know your thoughts about this.

What’s next?

The biggest parts of the work have been done, here is what is still on our TODO list until the release:

This is great – I want to participate in this

Please join us in the #flux channel on CNCF Slack ( get an invite here) to discuss this.

Or find out other ways of connecting (including our weekly meetings) on our Community page.

We are looking forward to having you in our community!