Does command operation in docker-compose.yml automatically search in entrypoint.sh? - docker

Question

I'm learning docker and here is part of the docker-compose.yml file for a project that I'm learning from:
services:
...
...
redis:
build: ./redis
image: smartjoe:redis
container_name: smartjoe--redis
command: redis-server
ports:
- '9993:6379'
volumes:
- /redis
volumes_from:
- data
data:
build: ./data
image: smartjoe:data
container_name: smartjoe--data
volumes:
- /data
- /var/lib/mysql
- /var/lib/redis/data
command: tail -f /dev/null
...
...
In the line command: redis-server under redis:, I was wondering where the redis-servercame from. After some search I was able to find that it is in a entrypoint.sh file located within the smartjoe--redis container:
/ # ls -la
total 68
drwxr-xr-x 1 root root 4096 Mar 28 21:24 .
drwxr-xr-x 1 root root 4096 Mar 28 21:24 ..
-rwxr-xr-x 1 root root 0 Mar 28 21:24 .dockerenv
drwxr-xr-x 1 root root 4096 Jun 28 2017 bin
drwxr-xr-x 4 redis redis 4096 Aug 2 19:51 data
drwxr-xr-x 5 root root 340 Aug 5 14:54 dev
lrwxrwxrwx 1 root root 34 Jun 28 2017 entrypoint.sh -> usr/local/bin/docker-entrypoint.sh
drwxr-xr-x 1 root root 4096 Mar 28 21:24 etc
drwxr-xr-x 1 root root 4096 Jun 28 2017 home
drwxr-xr-x 1 root root 4096 Jun 28 2017 lib
drwxr-xr-x 5 root root 4096 Jun 25 2017 media
drwxr-xr-x 2 root root 4096 Jun 25 2017 mnt
dr-xr-xr-x 229 root root 0 Aug 5 14:54 proc
drwxr-xr-x 2 root root 4096 Sep 7 2018 redis
drwx------ 1 root root 4096 Aug 5 18:14 root
drwxr-xr-x 2 root root 4096 Jun 25 2017 run
drwxr-xr-x 1 root root 4096 Jun 28 2017 sbin
drwxr-xr-x 2 root root 4096 Jun 25 2017 srv
dr-xr-xr-x 13 root root 0 Aug 1 16:00 sys
drwxrwxrwt 1 root root 4096 Jun 28 2017 tmp
drwxr-xr-x 1 root root 4096 Jun 28 2017 usr
drwxr-xr-x 1 root root 4096 Jun 28 2017 var
And the content of entrypoint.sh looks like:
/ # cat entrypoint.sh
#!/bin/sh
set -e
# first arg is `-f` or `--some-option`
# or first arg is `something.conf`
if [ "${1#-}" != "$1" ] || [ "${1%.conf}" != "$1" ]; then
set -- redis-server "$#"
fi
# allow the container to be started with `--user`
if [ "$1" = 'redis-server' -a "$(id -u)" = '0' ]; then
chown -R redis .
exec su-exec redis "$0" "$#"
fi
exec "$#"
My question is: I don't see entrypoint.sh being referenced anywhere in the docker-compose.yml script, does docker just assume there is a such entrypoint.sh file and search the key word after command: in the file?
btw, the Dockerfile is quite simple:
Bob#MacBook-Pro:~/smartjoe/smartjoe-local/docker/redis$ cat Dockerfile
FROM redis:3.0-alpine
MAINTAINER smartjoe Engineering "engineering#smartjoe.com"
Bob#MacBook-Pro:~/smartjoe/smartjoe-local/docker/redis$

Answer 1

The entrypoint would have been defined in the image, smartjoe:redis. Setting from the Dockerfile are a default that you can override in the docker-compose.yml. You can see the image configuration by inspecting the image, e.g.
docker image inspect smartjoe:redis