Building a docker container in a gitlab ci job

Question

I am trying to build a docker image as part of a gitlab ci job. I work on my own gitlab instance with a separate machine running ci jobs. I have tried and failed with many different configurations for using Docker in Docker. My current try is the method from this blog post: https://medium.com/@tonywooster/docker-in-docker-in-gitlab-runners-220caeb708ca

When executing a CI job on this runner with the docker command I get the following error:

ERROR: Failed to remove network for build
ERROR: Preparation failed: Cannot connect to the Docker daemon at tcp://gitlab-dind:2375. Is the docker daemon running? (docker.go:745:240s)

Why is that and how can I fix it? I am also happy with any other working method to build and push a docker container in my CI job. I am happy to provide any further information, but I am not sure what would help and don’t want to bloat the post.

As requested my gitlab CI file looks like this:

image: docker
stages:

package
test
push

build docker image:
  stage: package
tags:
    - docker
script: 
    - cat /proc/self/cgroup
    - docker info
    - docker build -t $CI_REGISTRY_IMAGE .
test docker image:
  stage: test
tags:
    - docker
script: 
    - docker run $CI_REGISTRY_IMAGE python testscript.py
push docker image:
  stage: push
tags:
    - docker
script:
    - docker tag $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
    - echo $CI_REGISTRY_PASSWORD | docker login -u $CI_REGISTRY_USER $CI_REGISTRY --password-stdin
    - docker push $CI_REGISTRY_IMAGE

Answer 1

To build a docker image in Gitlab runner, I recommend using kaniko instead of "docker in docker". Please read the official document of kaniko with Gitlab runner.

https://docs.gitlab.com/ee/ci/docker/using_kaniko.html

Answer 2

I wrote how to perform Docker build in GitLab Self-Hosted Runners Demo article. It uses docker in docker approach.

.gitlab-ci.yml is below:

stages:          # List of stages for jobs, and their order of execution
  - build
services:

name: docker:20.10.16-dind 
command: ["--mtu=1300"]

build:

  tags: [docker-on-prem]
  image: docker:20.10.16
  stage: build
  variables:
    DOCKER_HOST: "tcp://docker:2376"
    DOCKER_TLS_CERTDIR: "/certs"
    DOCKER_TLS_VERIFY: "1"
    DOCKER_CERT_PATH: "$DOCKER_TLS_CERTDIR/client"
  script:
- docker build -t test .

Sample repository with Dockerfile which you can fork and try the pipeline is at https://gitlab.com/warrior7089/gitlab-self-hosted-runners-demo/