test(docker): failover drill script — SIGKILL the active central node, assert Traefik recovery

deployments/docker-cluster.md

@@ -127,3 +127,4 @@ All passwords are `password`. See `infra/glauth/config.toml` for the full list.
 - Reference deployment for the project — when a change ships, it gets validated here first.
 - Concurrent with [`docker-cluster-env2`](docker-cluster-env2.md) on the same host; the two stacks share the `scadabridge-net` network and `infra/` services but use disjoint host ports (`90XX` vs `91XX`) and databases.
 - Detailed setup, failover testing, and build-cache notes live in [`docker/README.md`](../docker/README.md).
+- Automated failover drill: [`docker/failover-drill.sh`](../docker/failover-drill.sh) SIGKILLs the active central node and asserts Traefik recovers to the survivor (~25s + Traefik health interval); see the "Automated failover drill" subsection in `docker/README.md`.

docker/README.md

@@ -270,6 +270,23 @@ All test passwords are `password`. See `infra/glauth/config.toml` for the full l
 
 ## Failover Testing
 
+### Automated failover drill (`failover-drill.sh`)
+
+```bash
+bash docker/failover-drill.sh
+```
+
+The scripted drill is the repeatable version of the manual steps below. It:
+
+1. Finds the **active** central node (via each node's `/health/active`).
+2. **`docker kill`s it — SIGKILL, the hard-crash path.** This is the exact scenario arch-review 01 found had *no* automatic recovery before the SBR downing provider was enabled (`Akka.Cluster.SBR.SplitBrainResolverProvider` is now named explicitly in HOCON); a `docker stop` would take the graceful `CoordinatedShutdown` path instead and would not prove crash recovery.
+3. Polls Traefik (`http://localhost:9000/health/active`, override with `TRAEFIK_URL`) until the survivor is routable, printing the observed failover time. Fails after `TIMEOUT_S` (default 90s).
+4. Dumps the survivor's singleton/oldest/downing log evidence, then restarts the victim so it **rejoins as a fresh incarnation** (Task 20's recovery loop).
+
+Expected failover: **~25s** (2s heartbeat + 10s detection + 15s stable-after) **plus the Traefik ~5s health-check interval**. The drill exercises S1 (SBR downing on hard crash), S3 (single active node routed through Traefik), and the Task 20 restart/rejoin contract. Requires a running cluster (`bash docker/deploy.sh`) and `curl` + `docker` on the host.
+
+> **Observed failover time:** _run after next deploy and record here_ (the script was validated with `bash -n`; no live cluster was up when it was committed).
+
 ### Central Failover
 
 ```bash

docker/failover-drill.sh

@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+# Failover drill against the running docker cluster (bash docker/deploy.sh first).
+# Kills the ACTIVE central node (docker kill = SIGKILL, the hard-crash path that
+# review 01 found had NO automatic recovery before the SBR downing provider was
+# enabled) and measures how long Traefik takes to route to the survivor.
+set -euo pipefail
+
+TRAEFIK_URL="${TRAEFIK_URL:-http://localhost:9000}"
+TIMEOUT_S="${TIMEOUT_S:-90}"
+
+active_container() {
+  if curl -sf -o /dev/null "http://localhost:9001/health/active"; then echo scadabridge-central-a
+  elif curl -sf -o /dev/null "http://localhost:9002/health/active"; then echo scadabridge-central-b
+  else echo "ERROR: no active central node found" >&2; exit 1; fi
+}
+
+VICTIM=$(active_container)
+echo "Active central node: ${VICTIM} — killing it (SIGKILL, crash path)"
+docker kill "${VICTIM}" > /dev/null
+START=$(date +%s)
+
+echo "Waiting for the survivor to become active through Traefik (${TRAEFIK_URL}/health/active)..."
+while true; do
+  ELAPSED=$(( $(date +%s) - START ))
+  if curl -sf -o /dev/null "${TRAEFIK_URL}/health/active"; then
+    echo "PASS: failover complete in ${ELAPSED}s (design budget ~25s + Traefik health interval)"
+    break
+  fi
+  if (( ELAPSED > TIMEOUT_S )); then
+    echo "FAIL: no active central node after ${ELAPSED}s — SBR/singleton handover did not recover" >&2
+    docker start "${VICTIM}" > /dev/null
+    exit 1
+  fi
+  sleep 1
+done
+
+SURVIVOR=$([ "${VICTIM}" = scadabridge-central-a ] && echo scadabridge-central-b || echo scadabridge-central-a)
+echo "Survivor singleton evidence (last 20 matching log lines from ${SURVIVOR}):"
+docker logs "${SURVIVOR}" 2>&1 | grep -Ei "singleton|oldest|Downing|Removed" | tail -20 || true
+
+echo "Restarting ${VICTIM} and waiting for it to rejoin..."
+docker start "${VICTIM}" > /dev/null
+sleep 5
+echo "Drill complete. Verify on the Health dashboard that both nodes show Up and the survivor is Primary."