Pick the container role with ROLE instead of a command

docker-compose.yml

@@ -28,13 +28,13 @@ services:
 
   web:
     <<: *app
-    command: sh start-web.sh
     ports:
       - "8000:8000"
 
   celery:
     <<: *app
-    command: celery -A dynamicweb worker -l info
+    environment:
+      ROLE: celery
 
 volumes:
   pgdata:

entrypoint.sh

@@ -47,4 +47,15 @@ for _ in range(60):
 sys.exit("postgres at %s:%s not reachable" % (host, port))
 PYEOF
 
-exec "$@"
+# Explicit arguments win (docker compose run web python manage.py shell);
+# otherwise ROLE decides what this container does: web (default), celery, or
+# migrate (run the migrations and exit).
+if [ "$#" -gt 0 ]; then
+    exec "$@"
+fi
+case "${ROLE:-web}" in
+    web)     exec sh start-web.sh ;;
+    celery)  exec celery -A dynamicweb worker -l "${CELERY_LOGLEVEL:-info}" ;;
+    migrate) MIGRATE_ONLY=True exec sh start-web.sh ;;
+    *)       echo "unknown ROLE '$ROLE' (web, celery, migrate)" >&2; exit 1 ;;
+esac