Will the application run as PID 1 and will signals be received if we bootstrap it in a entrypoint.sh?

Question

It\'s good practice to start the service with

CMD [\"/go/bin/myapp\"]

instead of

CMD /go/bin/myapp

In the

Answer 1

Here is my try to follow what also the MySQL 5.7 Dockerfile does... but with an Nginx image.

Dockerfile:

FROM nginx:latest
COPY docker-entrypoint.sh /usr/local/bin/
RUN chmod 777 /usr/local/bin/docker-entrypoint.sh

ENTRYPOINT ["docker-entrypoint.sh"] 
EXPOSE 80
CMD ["nginx", "-g", "daemon off;"]

docker-entrypoint.sh:

#!/bin/bash
set -e

echo "preparing..."

exec "$@"

The idea is to do anything needed as a preparation inside the docker-entrypoint.sh script and with exec "$@" you then pass the signals to the CMD. (This means that you will have to use envsubst < /etc/nginx/conf.d/site.template > /etc/nginx/conf.d/default.conf inside docker-entrypoint.sh)

---

Link of relevant example to Dockerfile docs: If you need to write a starter script for a single executable, you can ensure that the final executable receives the Unix signals by using exec and gosu commands...

Answer 2

Quoting the tini GitHub page:

If you are using Docker 1.13 or greater, Tini is included in Docker itself. This includes all versions of Docker CE. To enable Tini, just pass the --init flag to docker run.

Or you can you use minit. It runs /etc/minit/startup on container startup and /etc/minit/shutdown when a container is stopped. I usually use this piece of code as entrypoint:

#!/bin/sh

if [ $# -gt 0 ] ; then
        exec "$@"
else
        exec /sbin/minit
fi