Install PHP composer in existing docker image - docker

Question

I'm running docker-letsencrypt through a docker-compose.yml file. It comes with PHP. I'm trying to run PHP composer with it. I can install composer while being in the container through bash, but that won't stick when I recreate the container. How do I keep a permanent install of composer in an existing container that doesn't come with compose by default?
My docker-compose.yml looks like this:
version: "3"
services:
letsencrypt:
image: linuxserver/letsencrypt
container_name: letsencrypt
cap_add:
- NET_ADMIN
ports:
- "80:80"
- "443:443"
environment:
- PUID=1000
- PGID=1000
- EMAIL=<mailadress>
- URL=<tld>
- SUBDOMAINS=<subdomains>
- VALIDATION=http
- TZ=Europe/Paris
volumes:
- /home/ubuntu/letsencrypt:/config
I did find the one-line installer for composer:
php -r "readfile('http://getcomposer.org/installer');" | php -- --install-dir=/usr/bin/ --filename=composer
I could add this to command in my docker-compose.yml, but that would reinstall composer even on container restarts right?

Answer 1

You're right about your comment about the command option, it will indeed be run every time you launch your container.
One workaround would be to create your own dockerfile, as follow :
FROM linuxserver/letsencrypt
RUN php -r "readfile('http://getcomposer.org/installer');" | php -- --install-dir=/usr/bin/ --filename=composer
(RUN directives are only run during the build step).
You should then modify your docker-compose.yml :
...
build: ./dir
#dir/ is the folder where your Dockerfile resides
#use the dockerfile directive if you use a non-default naming convention
#or if your Dockerfile isn't at the root of your project
container_name: letsencrypt
...