[Feature] Read Redis password from Kubernetes Secret

[kevin85421]

Why are these changes needed?

#949

Related issue number

Closes #949

Checks

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

# Step 1: Install a KubeRay operator
# Step 2: Create a RayCluster (path: ray-operator/config/samples)
kubectl apply -f ray-cluster.external-redis.yaml

# Step 3: Log in to the head Pod
kubectl exec -it ${HEAD_POD} -- bash
echo $RAY_REDIS_PASSWORD
# 5241590000000000

[kevin85421]

cc @scv119 @JoshKarpel

[JoshKarpel]

Looks good to me!

Just to make sure I understand the pattern - you're passing the string $RAY_REDIS_PASSWORD as a start param, and that gets evaluated at runtime because these values end up going (unescaped) into a sh -c? The actual RAY_REDIS_PASSWORD env var does not get picked up internally by Ray.

If so, this might be a good pattern to capture somewhere in the docs in text (using env vars to pass information via start params). It might also be good to pick up the RAY_REDIS_PASSWORD env var in Ray directly so that you don't need the indirection of the start param (perhaps related to the comment here #949 (comment)).

[kevin85421]

KubeRay operator will create Pod's command and args based on rayStartParams. In addition, Kubernetes also supports to use environment variables in a Pod's configuration elsewhere in the configuration (See here fore more details.).

The following figure is the command and args for the head Pod.

[JoshKarpel]

Great, thanks!