Is it possible to override config for a rollout experiment using specRef?

[cdapprich-bt]

I have a rollout that references an existing deployment (workloadRef), using the canary strategy with an inline experiment defined. The experiment uses specRef: canary, which means that the preview pod that the experiment runs against will also use the existing deployment spec from the workloadRef. Is it possible to override/specify the config of JUST the experiment pod, without manually defining the entire spec, replacing specRef?

---
apiVersion: argoproj.io/v1alpha1
kind: Rollout
spec:
. . .
  workloadRef:
    apiVersion: apps/v1
    kind: Deployment
    name: my-deployment
  strategy:
    canary:
      steps:
        - experiment:
            duration: 5m
            templates:
              - name: preview
                replicas: 1
                specRef: canary
                # is it possible to do something like this? (fails as-written)
                spec:
                  containers:
                    - name: primary
                      envFrom:
                        - configMapRef:
                            name: config-for-experiment-only
            analyses:
              . . .

I did find Analysis Template Arguments, but I believe this isn't quite right, as it only provides the arguments to the analysis run, not the experiment pod itself, correct?

[kostis-codefresh]

Could you explain a bit what is the business case here and what you are trying to achieve please?

[cdapprich-bt]

As an aside, we're currently planning to circumvent this issue entirely by using header-based routing. That way, we can just use the same OIDC issuer setting as in prod, but include a custom header so that requests from the analyses are routed to the canary/experiment pod instead of the stable one.

However, we'd still prefer a simpler, config-based solution - if one exists.

[kostis-codefresh]

Have you seen https://argo-rollouts.readthedocs.io/en/stable/features/ephemeral-metadata/ and the Kubernetes downward API ?

You can use them to make the canary pods "aware" that a canary is in progress and load whatever special configuration you want

[cdapprich-bt]

That sounds similar to what I'm looking for - is there any documentation or examples on how to use these metadata labels to load special config?

[kostis-codefresh]

Example 1 where canary pods connect to different queue

• guide - https://codefresh.io/blog/progressive-delivery-for-stateful-services-using-argo-rollouts/
• repo - https://github.com/kostis-codefresh/argo-rollouts-stateful-example/blob/main/manifests/stateful-rollout/worker.yml#L27

Example 2 where canary pods connect to different service

• guide - https://codefresh.io/blog/multi-service-progressive-delivery-with-argo-rollouts/
• repo - https://github.com/kostis-codefresh/multi-service-argo-rollouts-example/blob/main/manifests/legacy/rollout-fe.yml#L26