Cannot connect to the Docker daemon at tcp://localhost:2375/. Is the docker daemon running. On GitLab

Question

I'm trying to build the CI pipeline in GitLab. I'd like to ask about making the docker work in GitLab CI.

From this issue: https://gitlab.com/gitlab-org/gitlab-runner/issues/4501#note_195033385

I'm follow the instruction for both ways. With TLS and not used TLS. But It's still stuck. Which in same error

Cannot connect to the Docker daemon at tcp://localhost:2375/. Is the docker daemon running

I've try to troubleshooting this problem. follow by below,

1. enable TLS

Which used .gitlab-ci.yml and config.toml for enable TLS in Runner.

This my .gitlab-ci.yml:

image: docker:19.03
variables:
  DOCKER_HOST: tcp://localhost:2375/
  DOCKER_DRIVER: overlay2
  DOCKER_TLS_CERTDIR: "/certs"
  IMAGE_NAME: image_name

services:
  - docker:19.03-dind

stages:
  - build

publish:
  stage: build
  script:
    - docker build -t$IMAGE_NAME:$(echo $CI_COMMIT_SHA | cut -c1-10) .
    - docker push $IMAGE_NAME:$(echo $CI_COMMIT_SHA | cut -c1-10)
  only:
    - master   

And this my config.toml:

[[runners]]
  name = MY_RUNNER
  url = MY_HOST
  token = MY_TOKEN_RUNNER
  executor = "docker"
  [runners.custom_build_dir]
  [runners.docker]
    tls_verify = false
    image = "docker:stable"
    privileged = true
    disable_entrypoint_overwrite = false
    oom_kill_disable = false
    disable_cache = false
    volumes = ["/certs/client", "/cache"]                      
    shm_size = 0

2. Disable TLS

.gitlab-ci.yml:

image: docker:18.09
variables:
  DOCKER_HOST: tcp://localhost:2375/
  DOCKER_DRIVER: overlay2
  DOCKER_TLS_CERTDIR: ""
  IMAGE_NAME: image_name

services:
  - docker:18.09-dind

stages:
  - build

publish:
  stage: build
  script:
    - docker build -t$IMAGE_NAME:$(echo $CI_COMMIT_SHA | cut -c1-10) .
    - docker push $IMAGE_NAME:$(echo $CI_COMMIT_SHA | cut -c1-10)
  only:
    - master   

And this my config.toml:

[[runners]]
  environment = ["DOCKER_TLS_CERTDIR="]

Anyone have idea?

Solution

You can see at the accepted answer.
Moreover, In my case and another one. Looks like the root cause it from the Linux server that GitLab hosted doesn't has permission to connect Docker. Let's check the permission connectivity between GitLab and Docker on your server.

Answer 1

You want to set DOCKER_HOST to tcp://docker:2375. It's a "service", i.e. running in a separate container, by default named after the image name, rather than localhost.

Here's a .gitlab-ci.yml snippet that should work:

# Build and push the Docker image off of merges to master; based off
# of Gitlab CI support in https://pythonspeed.com/products/pythoncontainer/
docker-build:
  stage: build

  image:
    # An alpine-based image with the `docker` CLI installed.
    name: docker:stable

  # This will run a Docker daemon in a container (Docker-In-Docker), which will
  # be available at thedockerhost:2375. If you make e.g. port 5000 public in Docker
  # (`docker run -p 5000:5000 yourimage`) it will be exposed at thedockerhost:5000.
  services:
   - name: docker:dind
     alias: thedockerhost

  variables:
    # Tell docker CLI how to talk to Docker daemon; see
    # https://docs.gitlab.com/ee/ci/docker/using_docker_build.html#use-docker-in-docker-executor
    DOCKER_HOST: tcp://thedockerhost:2375/
    # Use the overlayfs driver for improved performance:
    DOCKER_DRIVER: overlay2
    DOCKER_TLS_CERTDIR: ""

  script:
    # Download bash:
    - apk add --no-cache bash python3
    # GitLab has a built-in Docker image registry, whose parameters are set automatically.
    # See https://docs.gitlab.com/ee/ci/docker/using_docker_build.html#using-the-gitlab-contai
    #
    # CHANGEME: You can use some other Docker registry though by changing the
    # login and image name.
    - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" "$CI_REGISTRY"
    - docker build -t "$CI_REGISTRY_IMAGE" .
    - docker push "$CI_REGISTRY_IMAGE"

  # Only build off of master branch:
  only:
    - master