Rename the swagger field from path-length to hop-count so the
generated Go struct field (PathLength → HopCount) and JSON key
(path-length → hop-count) align with the Prometheus metric rename
to goldpinger_peers_hop_count from the previous commit.
Signed-off-by: Cooper Ry Lees <me@cooperlees.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Add an opt-in UDP echo probe that runs alongside the existing HTTP
ping. Each goldpinger pod listens on a configurable UDP port (default
6969). During each ping cycle, the prober sends N sequenced packets
to the peer's listener, which echoes them back. From the replies we
compute packet loss percentage, path hop count (from IPv4 TTL / IPv6
HopLimit), and average round-trip time.
New Prometheus metrics:
- goldpinger_peers_loss_pct (gauge) — per-peer UDP loss %
- goldpinger_peers_path_length (gauge) — estimated hop count
- goldpinger_peers_udp_rtt_ms (histogram) — UDP RTT in milliseconds
The graph UI shows yellow edges for links with partial loss, and
displays sub-millisecond UDP RTT instead of HTTP latency when UDP
is enabled. Stale metric labels are cleaned up when a pinger is
destroyed so rolled pods don't leave ghost entries.
Configuration (all via env vars, disabled by default):
UDP_ENABLED=true enable UDP probing and listener
UDP_PORT=6969 listener port
UDP_PACKET_COUNT=10 packets per probe
UDP_PACKET_SIZE=64 bytes per packet
UDP_TIMEOUT=1s probe timeout
New files:
pkg/goldpinger/udp_probe.go — echo listener + probe client
pkg/goldpinger/udp_probe_test.go — unit tests
Unit tests:
```
=== RUN TestProbeUDP_NoLoss
udp_probe_test.go:51: avg UDP RTT: 0.0823 ms
--- PASS: TestProbeUDP_NoLoss (0.00s)
=== RUN TestProbeUDP_FullLoss
--- PASS: TestProbeUDP_FullLoss (0.00s)
=== RUN TestProbeUDP_PacketFormat
--- PASS: TestProbeUDP_PacketFormat (0.00s)
=== RUN TestEstimateHops
--- PASS: TestEstimateHops (0.00s)
PASS
```
Cluster test (6-node IPv6 k8s, UDP_ENABLED=true):
```
Prometheus metrics (healthy cluster, 0% loss):
goldpinger_peers_loss_pct{...,pod_ip="fd00:4:69:3::3746"} 0
goldpinger_peers_path_length{...,pod_ip="fd00:4:69:3::3746"} 0
Simulated 50% loss via ip6tables DROP in pod netns on node-0:
goldpinger_peers_loss_pct{instance="server",...} 60
goldpinger_peers_loss_pct{instance="node-1",...} 30
goldpinger_peers_loss_pct{instance="server2",...} 30
UDP RTT vs HTTP RTT (check_all API):
node-0 -> server: udp=2.18ms http=2ms
node-2 -> node-2: udp=0.40ms http=1ms
server -> node-0: udp=0.55ms http=2ms
Post-rollout stale metrics cleanup verified:
All 36 edges show 0% loss, no stale pod IPs.
```
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Cooper Ry Lees <me@cooperlees.com>
