jedarden bddfeb366c P6.2: Verify peer discovery implementation (plan §14.5)

Verified that peer discovery via headless Service + Downward API is
fully implemented:

- Helm templates: miroir-headless.yaml Service + POD_NAME/POD_IP env vars
- Rust module: peer_discovery.rs with SRV lookup via trust-dns-resolver
- Config: peer_discovery section with service_name + refresh_interval_s
- Main loop: Background refresh task that updates miroir_peer_pod_count metric
- Metrics: miroir_peer_pod_count, miroir_leader, miroir_owned_shards_count gauges
- Verification script: tests/verify_p6_2_peer_discovery.sh (NixOS-compatible shebang)

All unit tests pass. The implementation requires a Kubernetes deployment
for full acceptance testing (3-pod discovery, scale events, pod eviction).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

2026-05-23 02:51:14 -04:00

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P6.2 Peer Discovery Implementation Verification

Summary

Verified that peer discovery per plan §14.5 is fully implemented:

1. Helm Templates ✓

charts/miroir/templates/miroir-headless.yaml - Headless Service with label selector
charts/miroir/templates/miroir-deployment.yaml - POD_NAME, POD_NAMESPACE, POD_IP env vars via Downward API

2. Rust Implementation ✓

crates/miroir-core/src/peer_discovery.rs - SRV-based peer discovery module
- PeerSet struct with peers: Vec<PeerId> and refreshed_at: Instant
- PeerDiscovery::refresh() method for SRV lookup
- Feature flag: peer-discovery (uses trust-dns-resolver)

3. Configuration ✓

crates/miroir-core/src/config.rs - PeerDiscoveryConfig struct
- service_name: "miroir-headless" (default)
- refresh_interval_s: 15 (default)
charts/miroir/values.yaml - Config section with same defaults

4. Main Loop Integration ✓

crates/miroir-proxy/src/main.rs (lines 407-438)
- Creates PeerDiscovery instance when POD_NAME is set
- Spawns background refresh loop with configurable interval
- Calls metrics.set_peer_pod_count(count) on successful refresh

5. Metrics ✓

crates/miroir-proxy/src/middleware.rs (line 823-825, 1582-1584)
- miroir_peer_pod_count gauge metric
- miroir_leader gauge metric
- miroir_owned_shards_count gauge metric

6. Verification Script ✓

tests/verify_p6_2_peer_discovery.sh - Checks metrics and env vars
- Shebang: #!/usr/bin/env bash (NixOS compatible)

Acceptance Tests (require K8s environment)

The following acceptance tests require a real Kubernetes deployment:

3-pod deployment: Each pod sees all 3 peer names within 30s of last pod ready
Scale 3→5: New peers discovered within refresh_interval_s × 2
Pod eviction: Crashed pod drops from peer set within refresh_interval_s × 2
Metric verification: miroir_peer_pod_count matches kube_deployment_status_replicas_ready

Unit Tests

All peer discovery unit tests pass:

test_peer_set_empty ✓
test_peer_set_with_peers ✓
test_srv_target_pod_name_extraction ✓

Implementation Notes

The peer discovery implementation was already complete in the codebase
No code changes were required - this task was verification-only
The peer-discovery feature flag must be enabled for SRV lookups to work
Peer discovery automatically disables when POD_NAME=unknown (local dev)

Plan §14.5 Alignment

Fully implements plan §14.5 "Peer discovery" with:

Headless Service SRV lookup mechanism
15-second refresh interval (configurable)
Zero-config operation (uses Downward API env vars)
No K8s API calls from pods
Transient double-work is acceptable (idempotent operations)

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