📖proposal for multi-az apiserver loadbalancer by sebltm · Pull Request #2660 · kubernetes-sigs/cluster-api-provider-openstack

sebltm · 2025-08-18T14:04:34Z

What this PR does / why we need it:

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

Special notes for your reviewer:

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

TODOs:

squashed commits
if necessary:
- includes documentation
- adds unit tests

/hold

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k8s-ci-robot · 2025-08-18T14:04:46Z

Hi @sebltm. Thanks for your PR.

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lentzi90 · 2025-09-18T05:41:39Z

/ok-to-test

lentzi90

Interesting proposal! It will need some polishing though.
I think all the links are broken, so that would perhaps be the first thing to fix.

lentzi90 · 2025-09-18T06:08:58Z

+  - status.apiServerLoadBalancers is populated alongside legacy status until further cleanup.
+- Disabling multi-AZ:
+  - Remove the mapping; controller maintains single-LB behavior.
+  - Per-AZ LBs are not automatically deleted; operators may clean up unused resources.


Why would we not clean them up automatically?

k8s-triage-robot · 2025-12-17T06:52:03Z

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/lifecycle stale

sebltm · 2025-12-29T08:22:16Z

/remove-lifecycle stale

lentzi90

Looking pretty good!
Could you squash the commits?

I would also be interested in other maintainers opinion on this.
/cc @mandre @stephenfin

Add a design proposal for first-class Multi-AZ support for the Kubernetes control plane LoadBalancer in CAPO. The feature reconciles one Octavia LoadBalancer per Availability Zone via an explicit AZ-to-Subnet mapping, registers control plane nodes with the LB in their AZ by default, and relies on external DNS multi-value A records for client-side failover.

lentzi90 · 2026-02-12T06:21:12Z

@nikParasyr have you seen this proposal? I would be interested in your thoughts, especially when considering v1beta2 changes we want to make (e.g. #2899).

nikParasyr

I have 3 main "concerns" here:

The change to OSC.status will be a breaking change as we will need to go from status.apiServerLoadBalancer to status.apiServerLoadBalancer[]. We could introduce is at as a new field and deprecate the other but its something to keep in mind.
There are some fields of the current api that are not covered by the proposal. For example .spec.apiServerFloatingIP. I suspect that being able to predefine the floating ip per LB/AZ would be nice as it would allow users to create the FIPs & records beforehand (or through a lifecycleHook) and let the cluster roll out nicely. This would affect the current v1beta2 proposed changes as we will probably have to opt for option 2 and might even have to change the managedLoadbalancer to a list.
The request in #2999 has to be incorporated in this proposal i think. It doesnt feel usable to me (but might be missing something as openstack deployments vary) if we can create LBs per AZ on different subnets but cannot put the control-plane nodes on these subnets.

My other concern is that this will be tricky to test in e2e, but lets see

nikParasyr · 2026-02-13T09:04:45Z

+   - Add observability for per-AZ LB counts and reconciliation timings (non-breaking).
+
+## Open questions
+- Should we add a future explicit field to declare the endpoint strategy (single VIP vs external DNS multi-A)? Current design preserves user-provided DNS and documents multi-A.


Not sure about the field, but there should be clear documentation on how to achieve the different strategies

sebltm · 2026-02-13T10:57:46Z

Thanks for the review feedback. I took a pass at addressing some of the comments.
Main changes:

operator-managed network/subnet responsibility is explicit
endpoint strategy is now strict in multi-AZ (explicit DNS controlPlaneEndpoint required)
status replacement/deprecation is now deferred to the v2 migrations
FIP behavior and scope boundaries are explicit (existing v1beta1 behavior retained; per-AZ endpoint/FIP API redesign deferred to ✨ v1beta2 Group apiServer related fields on OpenStackCluster #2899)
alignment with Support multiple subnets for control-plane nodes across Availability Zones (similar to CAPA) #2999 is documented as complementary (no same-subnet requirement, but explicit reachability prerequisites)

Let me know if that aligns with that you were thinking

lentzi90

I am happy with this now. Let's see what others think.
/approve

k8s-ci-robot · 2026-03-26T05:11:41Z

[APPROVALNOTIFIER] This PR is APPROVED

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lentzi90 · 2026-04-15T07:38:11Z

/cc @bnallapeta

github-project-automation bot added this to CAPO Roadmap Aug 18, 2025

github-project-automation bot moved this to Inbox in CAPO Roadmap Aug 18, 2025

k8s-ci-robot added the do-not-merge/hold Indicates that a PR should not merge because someone has issued a /hold command. label Aug 18, 2025

k8s-ci-robot added cncf-cla: yes Indicates the PR's author has signed the CNCF CLA. size/L Denotes a PR that changes 100-499 lines, ignoring generated files. needs-ok-to-test Indicates a PR that requires an org member to verify it is safe to test. labels Aug 18, 2025

k8s-ci-robot requested review from lentzi90 and mdbooth August 18, 2025 14:04

sebltm mentioned this pull request Aug 18, 2025

[Feature Request] Allow provisioning one Load Balancer per Availability Zone for multi-AZ deployments #2488

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k8s-ci-robot added ok-to-test Indicates a non-member PR verified by an org member that is safe to test. and removed needs-ok-to-test Indicates a PR that requires an org member to verify it is safe to test. labels Sep 18, 2025

lentzi90 reviewed Sep 18, 2025

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k8s-ci-robot added the lifecycle/stale Denotes an issue or PR has remained open with no activity and has become stale. label Dec 17, 2025

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lentzi90 reviewed Jan 28, 2026

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Comment thread docs/proposals/20250818-multi-az-apiserver-loadbalancer.md Outdated

k8s-ci-robot requested review from mandre and stephenfin January 28, 2026 07:02

sebltm force-pushed the multi-az-lb-proposal branch from de80459 to 660f634 Compare February 8, 2026 18:42

lentzi90 mentioned this pull request Feb 12, 2026

Support multiple subnets for control-plane nodes across Availability Zones (similar to CAPA) #2999

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nikParasyr reviewed Feb 13, 2026

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fix: attempt to address comments

b0ee6ad

lentzi90 reviewed Mar 26, 2026

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k8s-ci-robot added the approved Indicates a PR has been approved by an approver from all required OWNERS files. label Mar 26, 2026

lentzi90 requested a review from nikParasyr April 15, 2026 07:38

k8s-ci-robot requested a review from bnallapeta April 15, 2026 07:38

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