Add topology aware deletion priority example

[Nakshatra480]

Fixes #198

Description

This PR introduces a comprehensive example of how to implement Topology Aware Deletion Priority for GameServers.

In scenarios where game scale down is driven by infrastructure consolidation rather than purely by game session logic (e.g., games with no clear match boundaries or free join/leave), it is crucial to prioritize deleting GameServers from nodes that are easier to empty. This optimization helps cluster autoscalers scale down nodes more efficiently, reducing infrastructure costs.

This implementation leverages the existing ServiceQuality probe mechanism to dynamically calculate and set the DeletionPriority without requiring any changes to the core controller code.

Solution Overview

The solution uses a sidecar/inline probe approach to query node metadata and calculate a priority score.

• Objective: Assign higher deletion priority to GameServers running on nodes with fewer pods and fewer pod owners.
• Mechanism: A ServiceQuality exec probe runs a script that queries the Kubernetes API for pod metrics on the current node.
• Integration: The probe result is passed to the DeletionPriority field using the ServiceQuality template variable {{.result}}.

Implementation Details

Two new example files are added in examples/topology-deletion-priority/:

1. rbac.yaml:

   • Defines a ServiceAccount, Role, and RoleBinding.
   • Grants minimal necessary permissions (list pods) to the GameServer so it can query topology information from the API server.

2. gameserverset.yaml:

   • Demonstrates a GameServerSet configuration.
   • Includes an inline script that:
     • Authenticates with the K8s API using the service account token.
     • Queries pods on the current node (spec.nodeName).
     • Calculates priority based on configurable weights.
   • Configures the ServiceQuality action to map the script output to deletionPriority.

Priority Calculation

The probe calculates the priority using the following logic:

# Weights (Configurable in script)
BASE_PRIORITY = 100
POD_WEIGHT = 10
OWNER_WEIGHT = 5

# Formula
DeletionPriority = BASE_PRIORITY - (PodCount * POD_WEIGHT) - (OwnerCount * OWNER_WEIGHT)

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[codecov]

Codecov Report

❌ Patch coverage is 40.38462% with 31 lines in your changes missing coverage. Please review.
✅ Project coverage is 40.26%. Comparing base (25626ff) to head (dadc058).

Files with missing lines	Patch %	Lines
pkg/controllers/gameserver/gameserver_manager.go	0.00%	16 Missing and 1 partial ⚠️
pkg/controllers/gameserver/topology_rater.go	60.00%	7 Missing and 7 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #313      +/-   ##
==========================================
+ Coverage   40.25%   40.26%   +0.01%     
==========================================
  Files         112      113       +1     
  Lines       12510    12559      +49     
==========================================
+ Hits         5036     5057      +21     
- Misses       7067     7087      +20     
- Partials      407      415       +8     

Flag	Coverage Δ
unittests	40.26% <40.38%> (+0.01%)	⬆️

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[Nakshatra480]

Hi @FillZpp @zmberg all the changes are done from my side. pls review this pr and let me know if anything comes up... thanks