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How do I fix a "Failed to connect to Docker daemon" error in my GitLab pipeline?

Are you encountering a "Failed to connect to Docker daemon" error in your GitLab pipeline? Don't worry, we've got you covered. This error typically occurs when the Docker engine cannot establish a connection, which can disrupt your pipeline and hinder the deployment process. Fortunately, there are a few steps you can take to resolve this issue and get your pipeline back on track.

Step 1: Verify Docker Engine Installation​

Firstly, ensure that Docker Engine is installed on the runner where your pipeline is executing. Check the installation and version to confirm that Docker is properly set up. Use the following command to check Docker version:

docker --version

Step 2: Restart Docker Service​

Sometimes, the Docker service may encounter issues that can lead to connection problems. Restarting the Docker service can often resolve such issues. Use the appropriate command for your operating system to restart Docker. For example, on a Linux system:

sudo systemctl restart docker

Step 3: Check Docker Socket Permissions​

The user running the GitLab Runner service might not have the necessary permissions to access the Docker socket. Grant the appropriate permissions to the user or group that executes the GitLab Runner. You can add the user to the docker group:

sudo usermod -aG docker $USER

After adding the user to the group, log out and log back in to apply the changes.

Step 4: Configure Docker-in-Docker (DinD)​

If you're using a Docker-in-Docker setup, ensure that the necessary configurations are in place. Verify that the DinD service is running and accessible from within your pipeline. Your .gitlab-ci.yml file should include the DinD service:

image: docker:latest
services:
  - docker:dind

variables:
  DOCKER_HOST: tcp://docker:2375/
  DOCKER_DRIVER: overlay2

before_script:
  - docker info

Step 5: Update GitLab Runner​

Outdated versions of GitLab Runner can sometimes cause compatibility issues with Docker. Update your GitLab Runner to the latest stable version to ensure compatibility with the Docker engine. Use the following commands to update GitLab Runner:

sudo gitlab-runner stop
sudo gitlab-runner uninstall
sudo curl -L --output /usr/local/bin/gitlab-runner https://gitlab-runner-downloads.s3.amazonaws.com/latest/binaries/gitlab-runner-linux-amd64
sudo chmod +x /usr/local/bin/gitlab-runner
sudo gitlab-runner install
sudo gitlab-runner start

Step 6: Verify Docker Daemon Status​

Check the status of the Docker daemon on the runner. Ensure that it is running without any errors or warnings. Use the following command to check Docker status:

sudo systemctl status docker

Troubleshoot any reported issues and resolve them accordingly.

Summary​

By following these steps, you should be able to resolve the "Failed to connect to Docker daemon" error in your GitLab pipeline. Remember to test your pipeline after implementing each step to confirm that the issue has been resolved.

If you continue to experience difficulties, feel free to reach out to our support team for further assistance. We're here to help you overcome any challenges and ensure smooth operation of your GitLab pipelines.

Keep building and deploying with confidence using Cloud-Runner, the high-performance GitLab runner solution designed to streamline your CI/CD workflows.