Docker Init Entrypoint

The script entrypoint.sh is a basic service init framework for containers. Entrypoint will source scripts in /k/start.d and /k/stop.d to start and stop services respectively.

The CMD directive of the dockerfile is an arbritrary command that will be executed in background. Entrypoint will wait on that process before shutting down.

Install

Use the ADD and ENTRYPOINT directive e.g.:

FROM debian:latest
ADD https://github.com/kronostechnologies/docker-init-entrypoint/releases/download/1.3.2/entrypoint.sh /usr/local/bin/entrypoint.sh
RUN chmod +x /usr/local/bin/entrypoint.sh
ENTRYPOINT ["/usr/local/bin/entrypoint.sh"]

Flow

Entrypoint follows a specific flow divided in two main part: starting/waiting on services(1,2) and stopping/killing services (3,4).

1. Source all the script in /k/start.d/ folder sorted according to string numerical value.
2. Execute and wait on the commands passed as parameter ($@) or, if no command are passed, sleep infinity. In docker, $@ correspond to the CMD directive.
3. Whenever SIGTERM, SIGQUIT or SIGINT is trapped, source all the script in /k/stop.d folder sorted according to string numerical value.
4. Send SIGTERM signal to any remaining process, excluding PID 1.

Environment variable

ENTRYPOINT_ROOT

If this variable is set, it will change the root directory of the start/stop scripts e.g.:

• ENTRYPOINT_ROOT="" scripts will be sourced from /start.d and /stop.d
• ENTRYPOINT_ROOT="/root" scripts will be sourced from /root/start.d and /root/stop.d.

Default is /k.

Bootstraping Folders

The bootstraping folders are /k/start.d/ and /k/stop.d which contains scripts to start and stop services respectively.

Here are some general advice about those scripts :

• Scripts must not be blocking (hanging).
• Scripts' name should start with three (3) digits 100_apache2.sh.

The CMD directive of the dockerfile is an arbritrary command that will be executed in background. The entrypoint will wait on that process before shutting down. Generally, CMD would be a command that would agregate logs to stdout such as tail. You can also use a custom script.

Note: you cannot set CMD to an interactive command. For exemple, setting /bin/bash as CMD will start a shell in the background and won't be accessible.

Examples

Examples can be found in the examples directory of this repository.

Troubleshoot

Error /usr/local/bin/entrypoint.sh: line 15: ps: command not found

Some base image such as debian "-slim" variant does not come with ps installed. Entrypoint needs ps to list remaining process so it can terminate them. Install ps with apt update && apt install procps -y in your image.