feat(chart): Adds topologySpreadConstraints for multi-zone HA

[Ayush4958]

Description

I had added native support for topologySpreadConstraints in the Helm chart to support highly available, multi zone deployments of the controller.

While users can technically inject soft podAntiAffinity rules into the existing affinity block, topologySpreadConstraints is the modern standard for guaranteeing balanced zone distribution without leaving replicas stuck in Pending.

Note on isolation: I placed this configuration alongside the existing affinity and tolerations blocks in values.yaml and deployment.yaml. This ensures it is completely structurally isolated and will not create merge conflicts with #411

Related Issue

Fixes #413

Type of Change

• New feature (non breaking)

Testing

• Added helm-unittest coverage in deployment_test.yaml asserting correct rendering of maxSkew and topologyKey when values are provided.
• make test passes locally.

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[kubernetes-prow]

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[ajaysundark]

I haven't seen many helm charts. I think we need to do some research on the need for this. It sounds like a good idea..but I wonder whether all of this are in general preset in the chart or operators would configure it for flexibility?

could you add a reference example, say a CNI controller, on what scheduling controls are expected from the chart?

Thanks for your time!

[Ayush4958]

hi @ajaysundark

These are never preset in chart because topology labels varies by environment (like AWS uses topology.kubernetes.io/zone, while bare metal might use a custom rack label) the standard way is to expose an empty array [] in values.yaml, so operators can inject their own specific constraints.

some references :-

• Cilium (CNI): values.yaml#L1040
• Ingress-Nginx: values.yaml#L638
• Cert-Manager: values.yaml#L192

It simply brings NRC to parity with the scheduling controls operators already expect from standard controllers

[ajaysundark]

Thanks @Ayush4958.

IIUC, the suggestion is to add this empty list, eg: https://github.com/cert-manager/cert-manager/blob/e7c1783d26ed1a3cf988170ccd96419045de5150/deploy/charts/cert-manager/values.yaml#L613-L624, so it's injectable via helm. Is that right?

[Ayush4958]

Yes, by exposing the [] in values.yaml operators can inject their own constraints.

[ajaysundark]

Just calling this out, currently the chart allows name-overrides, maybe a x-ref to the variable name as comment?

[Ayush4958]

yes, It will be nice
I will add the comment for adjustment , something like this :-

Note: Adjust this if you use nameOverride/fullnameOverride

[ajaysundark]

/lgtm

[ajaysundark]

it'd be good to mention this in our helm documentation when ready.

[Ayush4958]

it'd be good to mention this in our helm documentation when ready.

I'll make sure to add a section about this
should I add the helm doc change in this or a small PR will be good ?

[kubernetes-prow]

New changes are detected. LGTM label has been removed.

[kubernetes-prow]

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