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miroir/notes/miroir-m9q.2.md
jedarden 7784076c82 P6.2: Peer discovery implementation verification notes 
Document that peer discovery was already implemented in prior commits
(e6cdd05 and 26c9521). All required components are in place:
- Headless Service with Downward API env vars
- SRV-based peer discovery in peer_discovery.rs
- Background refresh loop in main.rs
- miroir_peer_pod_count metric in middleware.rs
- Verification script

Acceptance criteria require multi-pod K8s deployment testing.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
2026-05-23 02:42:42 -04:00

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P6.2 Peer Discovery Implementation Summary

Status: Already Implemented

The peer discovery feature described in the task was already implemented in prior commits:

  • e6cdd05 - P6.2: Fix peer discovery DNS SRV service name and add test
  • 26c9521 - P6.2: Fix peer discovery DNS SRV service name and add POD_IP

Implementation Checklist

Helm Chart

  • charts/miroir/templates/miroir-headless.yaml - Headless Service with label selector
  • charts/miroir/templates/miroir-deployment.yaml - Downward API env vars (POD_NAME, POD_NAMESPACE, POD_IP)
  • charts/miroir/templates/_helpers.tpl - Auto-derived service_name default using miroir.fullname
  • charts/miroir/values.yaml - peer_discovery config with auto-documented defaults

Rust Code

  • crates/miroir-core/src/peer_discovery.rs - SRV lookup implementation with trust-dns-resolver
  • crates/miroir-core/src/config.rs - PeerDiscoveryConfig struct
  • crates/miroir-proxy/src/main.rs - Background refresh loop (every 15s by default)
  • crates/miroir-proxy/src/middleware.rs - miroir_peer_pod_count metric

Verification

  • tests/verify_p6_2_peer_discovery.sh - Verification script for metrics and env vars
  • Unit tests in peer_discovery.rs - test_srv_target_pod_name_extraction, test_peer_set_empty, test_peer_set_with_peers

Acceptance Criteria

The following acceptance criteria require a multi-pod Kubernetes deployment to verify:

  1. 3-pod deployment: each pod sees all 3 peer names within 30s of last pod ready

    • Requires real K8s cluster with 3-pod deployment
    • Verification: Check logs for "peer discovery refresh completed" with peer_count=3

  2. Scale 3→5: new peers discovered within refresh_interval_s × 2

    • Requires real K8s cluster with scale operation
    • Verification: Scale deployment and observe peer_count update

  3. Pod eviction: crashed pod drops from peer set within refresh_interval_s × 2

    • Requires real K8s cluster with pod deletion
    • Verification: Delete pod and observe peer_count decrease

  4. miroir_peer_pod_count gauge matches kube_deployment_status_replicas_ready

    • Requires real K8s cluster with Prometheus scraping
    • Verification: Compare metrics endpoint with deployment status

These are integration tests that should be run in a staging environment. The verification script covers local development smoke testing.

Notes

  • The SRV lookup uses _http._tcp.<service>.<namespace>.svc.cluster.local format
  • Pod names are extracted from the first component of SRV target FQDNs
  • The implementation uses the system DNS resolver configuration from /etc/resolv.conf
  • Transient double-work during the 15-second discovery window is acceptable per plan §14.5