• We want to provide our product container image that includes two processes to make our product work properly.
• We don't want users to remove one of two processes. Because it causes some unexpected issues and our product does not work properly.
• We want to confirm whether we can satisfy the above two requirements or not by using supervisor.

• Build sample apps

  go build -o app1/app1 app1/app1.go
  go build -o app2/app2 app2/app2.go

• Build first container image

  docker build -t example.com/test/supervisor:latest .

• Build second container image (testing for overriding entrypoint)

  docker build -t example.com/test/supervisor-override:latest -f Dockerfile-Override-Entrypoint-Test .

1. Start container.

   docker run -d --name supervisor example.com/test/supervisor:latest

2. You can see the COMMAND (i.e., PID=1) is supervisord.

   $ docker ps -n 1
   CONTAINER ID   IMAGE                                COMMAND                  CREATED              STATUS              PORTS     NAMES
   82d9db06840f   example.com/test/supervisor:latest   "/usr/bin/supervisord"   About a minute ago   Up About a minute             supervisor

3. You also can see the app1 and app2 are running in the container.

   $ docker logs supervisor | tail -n 4
   2023-07-28 01:30:40.990770232 +0000 UTC m=+184.067225134
   App 1
   2023-07-28 01:30:40.990766091 +0000 UTC m=+184.067022370
   App 2

You can run app1 (or app2) only by overriding entrypoint.

1. Start container with --entrypoint option.

   docker run -d --name app1 --entrypoint /foo/app1 example.com/test/supervisor:latest

2. You can see the COMMAND (i.e., PID=1) is app1.

   $ docker ps -n 2
   CONTAINER ID   IMAGE                                COMMAND                  CREATED         STATUS         PORTS     NAMES
   aed1027dd695   example.com/test/supervisor:latest   "/foo/app1"              6 seconds ago   Up 5 seconds             app1
   82d9db06840f   example.com/test/supervisor:latest   "/usr/bin/supervisord"   6 minutes ago   Up 6 minutes             supervisor

3. You also can see only app1 is running in the container.

   $ docker logs app1 -n 8
   2023-07-28 01:35:26.71205839 +0000 UTC m=+112.042968652
   App 1
   2023-07-28 01:35:27.712609824 +0000 UTC m=+113.043520073
   App 1
   2023-07-28 01:35:28.712939735 +0000 UTC m=+114.043849988
   App 1
   2023-07-28 01:35:29.71340331 +0000 UTC m=+115.044313561
   App 1

You can run app1 (or app2) only by using re-builded container image.

1. Start container.

   docker run -d --name re-build-image example.com/test/supervisor-override:latest

2. You can see the COMMAND (i.e., PID=1) is app1.

   $ docker ps -n 3
   CONTAINER ID   IMAGE                                         COMMAND                  CREATED          STATUS          PORTS     NAMES
   f393bb2b715b   example.com/test/supervisor-override:latest   "/foo/app1"              6 seconds ago    Up 5 seconds              re-build-image
   aed1027dd695   example.com/test/supervisor:latest            "/foo/app1"              4 minutes ago    Up 4 minutes              app1
   82d9db06840f   example.com/test/supervisor:latest            "/usr/bin/supervisord"   10 minutes ago   Up 10 minutes             supervisor

3. You also can see only app1 is running in the container.

   $ docker logs re-build-image -n 8
   2023-07-28 01:39:17.716371433 +0000 UTC m=+50.017909408
   App 1
   2023-07-28 01:39:18.716841711 +0000 UTC m=+51.018379688
   App 1
   2023-07-28 01:39:19.717266353 +0000 UTC m=+52.018804331
   App 1
   2023-07-28 01:39:20.717722276 +0000 UTC m=+53.019260254
   App 1

It seems that removing one of two processes is easy. So, I think it is a bit difficult to achieve the following requirement.

• We don't want users to remove one of two processes. Because it causes some unexpected issues and our product does not work properly.