Exit code 1 occurs when Rails is stopped in Docker environment

problem

If you try to stop the container with docker stop while Rails (Puma) is running on Docker, you will get Exit 1 (SIGHUP). If you are using ECS or Kubernetes, the container may not terminate properly and may cause unexpected problems.

% docker ps -a
CONTAINER ID        IMAGE                     COMMAND                  CREATED             STATUS                      PORTS               NAMES
xxx        rails                      "bundle exec rails s…"   44 seconds ago      Exited (1) 3 seconds ago                        api
xxx

Cause

The cause is the so-called "PID 1 problem [^ 1]". PID 1 is called the init process, which is a special process called by the kernel at system startup. The init process handles signals, spawns child processes, deletes zombie processes, and more. This time, when Rails ([^ 2]) was started, PID 1 was used, and there was a problem that the signal could not be handled correctly.

#The result of executing the top command on the container
  PID USER      PR  NI    VIRT    RES  %CPU  %MEM     TIME+ S COMMAND
    1 root      20   0    2.2m   1.5m   0.0   0.1   0:00.02 S /bin/bash /bin/docker-entrypoint.sh bundle exec rails s -b 0.0.0.

If you look at the process, you can see that Rails is running with PID 1.

Countermeasures

As a child process of PID 1 by using a program such as tini or [dumb-init](https://github.com/ Yelp/dumb-init) It will be possible to start the application. If docker-compose 3.7 or later is available, you can work around the problem by adding the init parameter to docker-compose.yml ([^ 3]).

#Rails starts as a child process of the init process
PID USER      PR  NI    VIRT    RES  %CPU  %MEM     TIME+ S COMMAND
1 root      20   0    1.0m   0.0m   0.0   0.0   0:00.03 S /sbin/docker-init -- /bin/docker-entrypoint.sh bundle exec rails s -b 0.0.0.0
6 root      20   0    2.2m   1.5m   0.0   0.1   0:00.00 S  `- /bin/bash /bin/docker-entrypoint.sh bundle exec rails s -b 0.0.0.0

Looking at the process after running docker-compose down, the container is stopped at 143 (SIGTERM).

% docker-compose ps
          Name                         Command                State     Ports
-----------------------------------------------------------------------------
api                 /bin/docker-entrypoint.sh  ...   Exit 143

If you are using ECS

Add initProcessEnabled: true ([^ 4]) to the task definition. initProcessEnabled is equivalent to --init in docker run.

If you are using Kubernetes

You can also use a lightweight init such as tini, but starting with Kubernetes 1.17 it seems that you can work around the problem by using Share Process Namespace ([^ 5]).