[Epic] Topology and affinity settings for applications in Cozystack

[lllamnyp]

Summary

As a Cozystack user, I want to configure topology and affinity settings for managed applications, so that I can control how replicas are scheduled across availability zones and nodes.

Problem

Currently, managed applications (PostgreSQL, Redis, Kubernetes clusters, etc.) rely on the default kube-scheduler configuration for pod placement. Users have no way to explicitly control:

• Whether replicas should be spread across availability zones (for HA)
• Whether replicas should be co-located in a single zone (for lower latency)
• Node affinity preferences based on labels

Proposed Solution

Add optional topology or affinity configuration to all managed application specs, allowing users to specify:

• Topology spread constraints - e.g., spread across zones, or keep in single zone
• Node affinity - e.g., prefer nodes with specific labels
• Pod anti-affinity - e.g., avoid co-locating replicas on the same node

Example configuration:

spec:
  topologyPolicy: spreadAcrossZones  # or: singleZone, spreadAcrossNodes
  nodeSelector:
    disktype: ssd

Applications to Update

• PostgreSQL
• Redis
• MongoDB
• Kubernetes (worker nodes)
• Virtual Machines
• Other stateful applications

Related

• Similar to the topologySpreadPolicy already implemented in the Elasticsearch PR (Add Elasticsearch managed service with ECK operator #1899)