[Feature] Allow RayCluster Helm chart to specify different images for different worker groups

[Darren221]

Why are these changes needed?

Prior to this pull request, the RayCluster Helm chart had uniform default images for various worker groups. This PR introduces a new feature that empowers users to designate distinct images for both worker groups and the head Pod. To ensure backward compatibility, the PR verifies if the "image" section is defined for each Pod. If an image isn't specified in values.yaml, the Pod's image defaults to the option provided at the outset of values.yaml.

Related issue number

Closes #1291

Checks

• I've made sure the tests are passing.
• Testing Strategy
  • Unit tests
  • Manual tests
  • This PR is not tested :(

Test 1:

(Link to values.yaml for test 1)

helm install kuberay-operator kuberay/kuberay-operator --version 0.6.0

# Create a RayCluster with 1 head, 1 worker, and 2 worker groups (smallgroup 1 & 2)
# In values.yaml, specify the images for head, worker, and different worker groups
helm install ray-cluster kuberay/helm-chart/ray-cluster --version 0.6.0 -f kuberay/helm-chart/ray-cluster/values.yaml

# Describe the Pod to check its image
# [Expected result]: each Pod has the same image as what was specified (shown in the attached screenshots)
kubectl describe pod $PodName

Test 2:

(Link to values.yaml for test 2)

helm install kuberay-operator kuberay/kuberay-operator --version 0.6.0

# Create a RayCluster with 1 head, 1 worker, and 2 worker groups (smallgroup 1 & 2)
# In values.yaml, specify the images for worker, and different worker groups. 
# However, in Test 2, the image for head wasn't specified, and the image repository was missed when specifying the image for the worker Pod (to test backward compatibility and error handling).
helm install ray-cluster kuberay/helm-chart/ray-cluster --version 0.6.0 -f kuberay/helm-chart/ray-cluster/values.yaml

# Describe the Pod to check its image
# [Expected result]: 
# The image for the head was the same as the default option since it was not specified in values.yaml. 
# Additionally, an error (InvalidImageName) appeared in the worker Pod's description due to a missed image repository specification. This was done to alert the user. 
# Apart from these points, the images for other Pods matched those of Test 1, in line with what was defined in values.yaml.
kubectl describe pod $PodName

[kevin85421]

What will happen if pullPolicy is not defined?

[kevin85421]

ImagePullPolicy is an optional field for Pod, and the default value is here.

[Darren221]

To find out the difference between Pod and this PR regarding the imagePullPolicy, two test cases are shown below with different values for the tag of the image.
In this PR, both the repository and tag must be provided when specifying the image section.

Regarding the imagePullPolicy:
if it's left unspecified and the tag isn't set to "latest", the default becomes "IfNotPresent". (As shown in the figure below)

values.yaml (tag: not latest)

However, if the tag is "latest" and imagePullPolicy is not set, the default is "Always". (As shown in the figure below)

values.yaml (tag: latest)

[nicklausbrown]

When this is merged, will it automatically build a newly available helm chart, or will this be included in a future release (e.g. 0.7.0)? @Darren221, thanks for the work here 😄 and @kevin85421 appreciate your work maintaining the project 😄

[kevin85421]

LGTM

[kevin85421]

When this is merged, will it automatically build a newly available helm chart, or will this be included in a future release (e.g. 0.7.0)? @Darren221, thanks for the work here 😄 and @kevin85421 appreciate your work maintaining the project 😄

Thank @nicklausbrown for reaching out! Currently, CI will not publish the nightly chart automatically, but the first release candidate for Ray Summit (mid Sept) will be out soon.