CLOUDP-347497: Single cluster Replica Set Controller Refactoring

[Julien-Ben]

CLOUDP-347497 - Single cluster Replica Set Controller Refactoring

Why this refactoring

The single-cluster RS controller was mixing two concerns:

• Kubernetes stuff (StatefulSets, pods, volumes)
• Ops Manager/MongoDB stuff (MongoDB processes, replication config)

This worked fine for single-cluster, but it's a problem when you think about multi-cluster:

• Multi-cluster has multiple StatefulSets (one per cluster) but only one logical ReplicaSet in Ops Manager
• The OM automation config doesn't care about how many K8s clusters you have or how the pods are deployed

So we need to separate these layers properly.

Main changes

1. Broke down the huge Reconcile() method

Before: ~300 lines of inline logic in Reconcile()

Now:

Reconcile()
  ├── reconcileMemberResources()        // Handles all K8s resource creation
  │   ├── reconcileHostnameOverrideConfigMap()
  │   ├── ensureRoles()
  │   └── reconcileStatefulSet()        // StatefulSet-specific logic isolated here
  │       └── buildStatefulSetOptions() // Builds STS configuration
  └── updateOmDeploymentRs()            // Handles Ops Manager automation config updates

This makes it way easier to understand what's happening and matches the multi-cluster controller structure.

2. Removed StatefulSet dependency from OM operations

Created new helper functions that work directly with MongoDB resources instead of StatefulSets:

• CreateMongodProcessesFromMongoDB() - was using StatefulSet before
• BuildFromMongoDBWithReplicas() - same
• WaitForRsAgentsToRegisterByResource() - same

These mirror the existing ...FromStatefulSet functions but take MongoDB resources instead.

Why it matters: The OM layer now only cares about the MongoDB resource definition, not how it's deployed in K8s. This makes the code work the same way for both single-cluster and multi-cluster.

3. Added publishAutomationConfigFirstRS checks

Dedicated function for RS instead of using the shared one. Does not rely on a statefulset object.

Important for review

The ideal way to review this PR is to compare the new structure to the mongodbmultireplicaset_controller.go. The aim of the refactoring is to get the single cluster controller closer to it.

Look at:

• reconcileMemberResources() in both controllers - similar structure now
• updateOmDeploymentRs() - no more StatefulSet dependency
• New helper functions in om/process and om/replicaset - mirror existing patterns

Bug found along the way

The logic to handle scale up + disable TLS at the same time doesn't actually work properly and should be blocked by validation (see draft PR #490 for more details).

Tests added

Added tests for the new helper functions:

• TestCreateMongodProcessesFromMongoDB - basic scenarios, scaling, custom domains, TLS, additional config
• TestBuildFromMongoDBWithReplicas - integration test checking ReplicaSet structure and member options propagation
• TestPublishAutomationConfigFirstRS - automation config publish logic with various TLS/auth scenarios

[github-actions]

⚠️ (this preview might not be accurate if the PR is not rebased on current master branch)

MCK 1.5.0 Release Notes

New Features

• Improve automation agent certificate rotation: the agent now restarts automatically when its certificate is renewed, ensuring smooth operation without manual intervention and allowing seamless certificate updates without requiring manual Pod restarts.

Bug Fixes

• MongoDBMultiCluster: fix resource stuck in Pending state if any clusterSpecList item has 0 members. After the fix, a value of 0 members is handled correctly, similarly to how it's done in the MongoDB resource.

[m1kola]

Early review: I had a quick-ish look at the controllers and couldn't spot anything obviously wrong with it. I didn't review the tests at all.

Looks good so far.

[Julien-Ben]

Brought it closer to where it's actually used

[Julien-Ben]

This comment was old (<2022)

[Julien-Ben]

I added these as helpers for myself at the beginning of the refactoring, to keep track of where I was in the hundreds of lines of the reconcile loop

I'm okay to remove them now if they feel like noise more than useful comments