Use a Deployment instead of a StatefulSet for the controller

[antonipp]

Description

While trying out the agent-sandbox project, I noticed that the main controller is deployed as a StatefulSet. I couldn't really find a justification for it in the commit history, so this looks like an oversight. The controller is stateless and doesn't require a stable network identity, so I don't really see a reason to use a much heavier abstraction here. Moreover, STS ordered rollout semantics are unnecessary for a stateless controller and could complicate scaling/updates if leader election is enabled for HA.

So my PR switches the controller to be deployed as a simple Deployment, I think it will make operations easier for everyone

Migration Guide

The controller changed from StatefulSet to Deployment and leader election is now enabled by default. Before you deploy the new charts, you need to clean-up the existing StatefulSet (this will cause a brief disruption to Sandbox state reconciliation):

kubectl delete statefulset agent-sandbox-controller -n agent-sandbox-system

Then deploy the new charts. Verify that the Deployment has been properly created:

kubectl get deployment agent-sandbox-controller -n agent-sandbox-system

If needed, the rollback steps are:

kubectl delete deployment agent-sandbox-controller -n agent-sandbox-system
kubectl apply -f <previous-version-manifest.yaml>

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[netlify]

✅ Deploy Preview for agent-sandbox canceled.

Name	Link
🔨 Latest commit	8fbc2d5
🔍 Latest deploy log	https://app.netlify.com/projects/agent-sandbox/deploys/6957cd3855abca00088a2f7a

[k8s-ci-robot]

Hi @antonipp. Thanks for your PR.

I'm waiting for a github.com member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[janetkuo]

/ok-to-test

[barney-s]

This is an acceptable change. We can switch back to sts later if needed. Would you check the docs and check if they need a change.

[barney-s]

Thanks for the changes

[barney-s]

While changing the kind to Deployment is the correct move for a stateless controller, this is a breaking change for existing users. An upgrade will not be smooth as the new Deployment won't manage the old StatefulSet's pods.

Please add a note to the RELEASE.md or a dedicated upgrade guide explaining the manual steps required, which likely involve deleting the old StatefulSet before applying the new manifests.

[antonipp]

I am aware it's a breaking change but not really sure what's the actual process for documenting it should be. RELEASE.md feels wrong and an upgrade guide is overkill for such as simple change (especially since the project is in the early days and users should expect the internals to change)

Maybe something we just call out in the Github release notes somehow?

[janetkuo]

@antonipp Would you document the migration step in the PR description?

[antonipp]

Yep, added a short migration guide to the PR description

[antonipp]

/retest

[janetkuo]

/label release-note-action-required

[k8s-ci-robot]

@janetkuo: The label(s) /label release-note-action-required cannot be applied. These labels are supported: api-review, tide/merge-method-merge, tide/merge-method-rebase, tide/merge-method-squash, team/katacoda, refactor, ci-short, ci-extended, ci-full. Is this label configured under labels -> additional_labels or labels -> restricted_labels in plugin.yaml?

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/label release-note-action-required

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[janetkuo]

@antonipp Would you document the migration step in the PR description?

[k8s-ci-robot]

@antonipp: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
presubmit-agent-sandbox-e2e-test	8fbc2d5	link	true	/test presubmit-agent-sandbox-e2e-test

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository. I understand the commands that are listed here.