Clone git repository with Docker

There are many ways to use Git with Docker, but this guide focuses on using SSH Deploy keys to clone a repository from GitLab or GitHub. as easily as possible.

I know there are many ways to do this, but I want to show you a simple way to do it.

Deploy keys

Deploy keys are used to give read-only access to a repository. Generate an entirely new SSH key pair for the deployment:

ssh-keygen -t ed25519 -C "deploy@gitlab.com" -P "" -f .ssh/id_ed25519

This command will generate a new SSH key pair without passphrase. Then you have to add the public key to the GitLab or GitHub

After adding the public key to the repository, you can test the connection:

ssh -o "IdentitiesOnly=yes" -i .ssh/id_ed25519 -Tvvv git@gitlab.com

Dockerfile

Create a Dockerfile with the following content:

FROM alpine/git:latest

---
title: Copy generated key pair to the container
---COPY --chown=root:root .ssh /root/.ssh

RUN ssh-keyscan gitlab.com >> /root/.ssh/known_hosts \
  && chown -R root:root /root/.ssh \
  && chmod 700 /root/.ssh \
  && chmod 600 /root/.ssh/*

---
title: Copy bin folder
---COPY entrypoint /usr/local/bin/entrypoint

---
title: App source code
---WORKDIR /app
VOLUME /app

ENTRYPOINT ["entrypoint"]

Let’s have a repository git@gitlab.com:your/app.git them your entrypoint file should look like this:

#!/usr/bin/env sh

---
title: repository does not exist, clone it
---if [ ! -d .git ]; then
  git clone git@gitlab.com:your/app.git --branch main --single-branch /app || exit 31
fi

---
title: Update the repository
---git fetch origin main || exit 32
git switch main   || exit 33
git reset --hard origin/main || exit 34

---
title: Clean up content except node_modules, vendor and .cache
---git clean -dfx --exclude node_modules --exclude vendor --exclude .cache || exit 35

---
title: Update submodules
---git submodule sync || exit 36
git submodule update --init --force || exit 37
echo "【ツ】Source code was updated!"

We can easily build git container using the compose.yml file:

services:
  git:
    build:
      context: .
      dockerfile: Dockerfile
    volumes:
      - ./source:/app

Run the following command to build the image and start the container:

docker compose up --build

Your repository will be cloned to the source folder.