kubernetes executor issue

Hi,

I am trying to configure gitlab CI on my kubernetes cluster, and applied the kubernetes executor. The ci config is simply as what in your document.

image: docker:stable

services:
  - docker:dind

variables:
  CONTAINER_IMAGE: registry.gitlab.com/$CI_PROJECT_PATH
  DOCKER_HOST: tcp://docker:2375
  DOCKER_DRIVER: overlay2

before_script:
    - docker info
 
build:
    stage: build
    script:
      - docker build -t my-docker-image .
      - docker run my-docker-image /script/to/run/tests

the errors of the job is as below

Running with gitlab-runner 10.3.0 (5cf5e19a)
  on runner-gitlab-runner-7954c5547d-znwmc (701975b6)
Using Kubernetes namespace: gitlab-managed-apps
Using Kubernetes executor with image docker:stable ...
Waiting for pod gitlab-managed-apps/runner-701975b6-project-447-concurrent-0tg89x to be running, status is Pending
Running on runner-701975b6-project-447-concurrent-0tg89x via runner-gitlab-runner-7954c5547d-znwmc...
Cloning repository...
Cloning into '/k8s/ci-cd-demo'...
Checking out db83422e as develop...
Skipping Git submodules setup
$ docker info
error during connect: Get http://docker:2375/v1.39/info: dial tcp: lookup docker on 100.64.0.10:53: no such host
ERROR: Job failed: error executing remote command: command terminated with non-zero exit code: Error executing in Docker Container: 1

Any idea about how to fix it?