whalewatcher

Recreate a Docker container if a container it depends upon is recreated.

That's a word salad, so here's at least one use case (mine):

You have a containerized app that routes traffic through a containerized VPN client, but when watchtower recreates the VPN client container due to an image update, your app container stops routing traffic until it is removed and recreated.

This small Dockerfile and shell script will monitor the state of containers in these dependent relationships and removes/recreates the dependent container as needed.

Environment variables

The following environment variables must be set; no defaults are provided.

Name	Description	Example value
DEPENDENT_CONTAINER	The container with the dependency	rtorrent
DEPENDENCY_CONTAINER	The container that is depended upon	vpn-dal
COMPOSE_PROJECT_NAME	The name of the compose project	rtorrent

The examples above suggest an rtorrent/docker-compose.yml that looks something like this:

version: "3.2"

services:
  rtorrent:
    image: crazymax/rtorrent-rutorrent
    container_name: rtorrent
    network_mode: container:vpn-dal
    # whatever environment variables and volumes you need

  watcher:
    image: treyturner/whalewatcher
    container_name: rtorrent_watcher
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
      # YOU MUST MODIFY THE HOST PATH TO CORRECTLY MOUNT YOUR docker-compose.yml INSIDE THE CONTAINER
      - /mnt/cache/appdata/portainer_data/compose/28/docker-compose.yml:/root/docker-compose.yml
    restart: unless-stopped
    environment:
      - DEPENDENT_CONTAINER=rtorrent
      - DEPENDENCY_CONTAINER=vpn-dal
      - COMPOSE_PROJECT_NAME=rtorrent

And here's what the container logs when it's doing its thing. In this case, it happened to poll before vpn-dal had reached it's safe init time (30 seconds), so it waits at least that long before starting the dependency.

2022-11-04 Fri 18:32:20 Waiting 10 seconds for vpn-dal to initialize...
2022-11-04 Fri 18:32:30 rtorrent was started before vpn-dal initialized. Recreating...
Stopping rtorrent ...
Stopping rtorrent ... done
Removing rtorrent ...
Removing rtorrent ... done
Going to remove rtorrent
Creating rtorrent ...
Creating rtorrent ... done