A simple container you can run that will serve a message with a 503 "Service Unavailable" status.
Scheduled Maintenance
This site is temporarily unavailable while we perform upgrades and maintenance.
Run the container on port 80:
docker run --init --rm -p:80:3000 maintenance-pageRun the container on port 80, with an additional message:
docker run --init --rm -e extraText='Contact foo@example.com for urgent issues.' -p:3000:3000 maintenance-page