Docker: docker-compose copy files from container to host - php

Question

I want to copy all files during the installation process in docker-compose.yml file.
If I run:
$ git clone https://github.com/laravel/laravel.git laravel-app
$ cd laravel-app
$ docker run --rm -v $(pwd):/app composer install
It will copy all new files from container to host during the installation process in the docker container.
So I will see new vendor folder and composer.lock file in my laravel-app directory after installation.
But if I setup volume in docker-compose.yml:
version: '3'
services:
#PHP Service
app:
build:
context: .
dockerfile: Dockerfile
container_name: app
restart: unless-stopped
tty: true
environment:
SERVICE_NAME: app
SERVICE_TAGS: dev
working_dir: /var/www
volumes:
- ./:/var/www
- ./php/local.ini:/usr/local/etc/php/conf.d/local.ini
networks:
- app-network
And then setup installation process in Dockerfile:
FROM php:7.4.4-fpm
# Set working directory
WORKDIR /var/www
# Install dependencies
RUN apt-get update && apt-get install -y
# Install composer
RUN curl -sS https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin --filename=composer
# Copy existing application directory contents
COPY . /var/www
# Install composer.json dependencies
RUN composer install # <<-- !this one!
It will not copy vendor folder and composer.lock file back to my host.
Hot to make it happen?

Answer 1

how about add composer docker image to your docker compose, and run command install
version: '3'
services:
#PHP Service
#your php image
# composer
composer:
image: composer/composer
volumes:
- ./:/var/www
command: install

Answer 2

You copy all build context into your image /var/www
You run composer install from the image, so vendor and composer.lock only exist in the image, not on your host
You bind mount your current directory(which has composer.json but not vendor and composer.lock) to /var/www, so it replaces the image /var/www
You know your issue, the fix depends on what you want to do exactly, tell me in a comment.
Tip: You should use Docker multi-stage builds to install Composer into your image. It's much cleaner than the curl
COPY --from=composer:latest /usr/bin/composer /usr/bin/composer
COPY . /var/www/
RUN composer install --no-scripts --no-suggest --optimize-autoloader