docker watcher

Dockers/docker-watcher/Dockerfile

@@ -0,0 +1,6 @@
+FROM docker:cli
+
+COPY watch.sh /watch.sh
+RUN chmod +x /watch.sh
+
+ENTRYPOINT ["/watch.sh"]

Dockers/docker-watcher/watch.sh

@@ -0,0 +1,56 @@
+#!/bin/sh
+set -eu
+
+WATCH_CONTAINER="${WATCH_CONTAINER:?set WATCH_CONTAINER to the container name or id to watch}"
+RESTART_CONTAINERS="${RESTART_CONTAINERS:?set RESTART_CONTAINERS to a comma-separated list of containers to restart}"
+POLL_INTERVAL="${POLL_INTERVAL:-30}"
+
+# Only restart when status *becomes* unhealthy (avoids restarting every poll while still unhealthy).
+# Set RESTART_ON_EVERY_POLL=1 to restart on every poll while unhealthy.
+RESTART_ON_EVERY_POLL="${RESTART_ON_EVERY_POLL:-0}"
+
+log() {
+  printf '%s %s\n' "$(date '+%Y-%m-%dT%H:%M:%S')" "$*"
+}
+
+inspect_health() {
+  docker inspect --format '{{if .State.Health}}{{.State.Health.Status}}{{else}}none{{end}}' "$1" 2>/dev/null || printf 'missing'
+}
+
+restart_list() (
+  IFS=','
+  for c in $RESTART_CONTAINERS; do
+    c=$(echo "$c" | sed 's/^[[:space:]]*//;s/[[:space:]]*$//')
+    [ -z "$c" ] && continue
+    if docker restart "$c" 2>/dev/null; then
+      log "restarted: $c"
+    else
+      log "restart failed: $c"
+    fi
+  done
+)
+
+prev=""
+log "watching health of: $WATCH_CONTAINER (interval ${POLL_INTERVAL}s)"
+log "will restart on unhealthy: $RESTART_CONTAINERS"
+
+while true; do
+  status="$(inspect_health "$WATCH_CONTAINER")"
+
+  case "$status" in
+    missing)
+      log "watch target not found: $WATCH_CONTAINER"
+      ;;
+    unhealthy)
+      if [ "$RESTART_ON_EVERY_POLL" = "1" ] || [ "$prev" != "unhealthy" ]; then
+        log "unhealthy — restarting configured containers"
+        restart_list
+      fi
+      ;;
+    *)
+      ;;
+  esac
+
+  prev="$status"
+  sleep "$POLL_INTERVAL"
+done