How to build an image of a project using docker-compose with Dockerfile?

Question

I have a project that is running in local development using docker-compose

As part of the organisation requirements for gitlab and deployment, the application needs to be built into a single Docker image.

I understand this can be done by adding a Dockerfile to the project.

However, I'm wondering if any advice or suggestions on how to include a project running multiple services via docker-compose with the application codebase into a single image with Dockerfile for deployment, thanks.

EDIT: From what I can gather, the approach would be to build a new image , with Dockerfile, from the application codebase, then include that in the docker-compose.yml file for the deployment environment?

EDIT 2: Apologies for the confusion. I'm new at Docker and there's a bit of learning curve! In this case it seems one can build the application image in the gitlab registry and then include that image in the docker-compose for deployment, will try it.

Answer 1

TL;DR

A single Dockerfile is usually not enough to replace a whole containers orchestration made with docker-compose and is not necessarly a good choice.

About converting a docker-compose.yml file to a Dockerfile :

You can pass some informations from your docker-compose.yml file to your Dockefile (the command to run for instance) but that wouldn't be equivalent and you can't do that with all the docker-compose.yml file content.

You can replace your docker-compose.yml file with commands lines though (as docker-compose is precisely to replace it).

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BUT

Keep in mind that Dockerfiles and docker-compose serve two whole different purposes.

• Dockerfile are meant for image building, to define the steps to build your images.

• docker-compose is a tool to start and orchestrate containers to build your applications (you can add some informations like the build context path or the name for the images you'd need, but not the Dockerfile content itself).

So asking to "convert a docker-compose.yml file into a Dockerfile" isn't really relevant.

That's more about converting a docker-compose.yml file into one (or several) command line(s) to start containers by hand.

The purpose of docker-compose is precisely to get rid of these command lines to make things simpler (it automates it).

Multiple processes in a single container :

From the docker documentation :

It’s ok to have multiple processes, but to get the most benefit out of Docker, avoid one container being responsible for multiple aspects of your overall application

So you can if your entrypoint permits you to launch several processes, or if you use a supervisor, but maybe that's not necessarly the best idea.

EDIT

Since I'm not sure it's clear for you either, here is the difference between a container and an image.

You really should check this out and try to understand this before working with Docker since it's a very necessary thing to know.