<p>It's a placeholder domain name for connecting over SSH. It doesn't mean that it's connecting to docker.example.com.</p>
<p>I ran into a similar error when using a Docker client over SSH. The error message was:</p>
<pre><code>ERROR: Cannot connect to the Docker daemon at http://docker.example.com. Is the docker daemon running?
</code></pre>
<p>Reading the <a href="https://github.com/docker/docker-ce/blob/ecc5c5c703293d6eb9b46ff8221bdec528832787/components/cli/cli/connhelper/connhelper.go#L52" rel="noreferrer">Docker source code</a>, it looks like &quot;docker.example.com&quot; is a placeholder host name when connecting over SSH, resulting in the confusing error message.</p>
<p>In my case, the error was caused by the user I was logging in as not being part of the docker group, and therefore not having permission to use docker.</p>

CC BY-SA 4.0
2021-12-19T11:56:37.600Z
Thank you for investigating this. So do you think this behavior is unexpected and therefore worth reporting as a bug? I think it is at least misleading when the actual problem is something else.
mcnesium
CC BY-SA 4.0
2021-12-19T16:33:40.627Z
@mcnesium Yes, I think that's confusing enough to count as a bug. Also, here's another person who ran into the same problem: https://forums.docker.com/t/docker-compose-through-ssh-failing-and-referring-to-docker-example-com/115165
Nick ODell
CC BY-SA 4.0
2021-12-19T16:59:45.353Z
When I saw this, I was copy-pasting an example into my terminal, so I thought I must have forgotten to change some placeholder. Spent a bunch of time looking for where I forgot to replace 'docker.example.com.'
Nick ODell
CC BY-SA 4.0
2023-07-14T06:15:07.640Z
This can occur when you have a multi-platform buildx setup that includes a remote machine. I do it to do x86+arm64 builds from an M1 Mac, with a remote x86 box doing the cross-platform build while my M1 does the arm64 build in parallel, each doing their thing without emulation. If I don't have Docker up on the remote host, I get this error.
Warren Young
CC BY-SA 4.0
2021-12-19T00:01:53.953Z
2022-10-17T21:57:10.243Z
2022-10-17T21:57:10.243Z
Nick ODell
<p>I am trying to have a Docker image deployed to my server by GitLab CI, but it only worked once¹ and then dies with the error message below. Here is the <code>.gitlab-ci.yml</code> snippet:</p>
<pre><code>deploy-image:
  image: docker:latest
  services:
    - docker:dind
  variables:
    DOCKER_HOST: ssh://gitlab-ci@$DEPLOY_HOST
  before_script:
    - eval $(ssh-agent -s)
    - echo &quot;${SSH_KEY}&quot; | ssh-add -
    - mkdir -p ~/.ssh
    - '[[ -f /.dockerenv ]] &amp;&amp; echo -e &quot;Host *\n\tStrictHostKeyChecking no\n\n&quot; &gt; ~/.ssh/config'
  script:
    - echo $CI_JOB_TOKEN | docker login --username gitlab-ci-token --password-stdin $CI_REGISTRY;
    - docker pull &quot;$CI_REGISTRY_IMAGE&quot;
    - docker run --name mycontainer --detach $CI_REGISTRY_IMAGE
  after_script:
    - docker logout $CI_REGISTRY
</code></pre>
<p>The error in the job log looks like that:</p>
<pre><code>Executing &quot;step_script&quot; stage of the job script 00:04
Using docker image sha256:51453dcdd9bd51e503f75e6d42a4071469ad2ba816321781985041b6bc7776db for docker:latest with digest docker@sha256:ddf0d732dcbc3e2087836e06e50cc97e21bfb002a49c7d0fe767f6c31e01d65f ...
$ eval $(ssh-agent -s)
Agent pid 18
$ echo &quot;${SSH_KEY}&quot; | ssh-add -
Identity added: (stdin) (gitlab-ci@jacks)
$ mkdir -p ~/.ssh
$ [[ -f /.dockerenv ]] &amp;&amp; echo -e &quot;Host *\n\tStrictHostKeyChecking no\n\n&quot; &gt; ~/.ssh/config
$ echo $CI_JOB_TOKEN | docker login --username gitlab-ci-token --password-stdin $CI_REGISTRY;
error during connect: Post &quot;http://docker.example.com/v1.24/auth&quot;: command [ssh -l gitlab-ci -- xxx.xxx.xxx.xxx docker system dial-stdio] has exited with exit status 255, please make sure the URL is valid, and Docker 18.09 or later is installed on the remote host: stderr=ssh: connect to host xxx.xxx.xxx.xxx port 22: Connection refused
</code></pre>
<p>While I x-ed out the IP address of the destination server in this post (which is the value of the <code>DEPLOY_HOST</code> env var), it literally says <strong>docker.example.com</strong> in the error message.</p>
<p>So my question would be, where that example string comes from.</p>
<p>This is on a self-hosted GitLab instance and the runner is also self-hosted on a server that is neither the destination host, nor the one where GitLab runs on.</p>
<p>¹ The connection issue itself seems to be a problem with the SSH connection and not related to the CI/CD pipeline config.</p>

CC BY-SA 4.0
2021-09-12T20:13:28.180Z
`Post "http://docker.example.com/v1.24/auth"` is likely coming from `docker login --username gitlab-ci-token --password-stdin $CI_REGISTRY;` - what's the value of $CI_REGISTRY
Sathyajith Bhat
CC BY-SA 4.0
2021-11-24T16:34:45.993Z
The value of `$CI_REGISTRY` is the container registry. It is a pre-defined variable that is specific to every project and defined automatically by GitLab CI, see https://docs.gitlab.com/ee/ci/variables/predefined_variables.html
(sorry for answering late)
mcnesium
<docker><gitlab><deployment><cicd>
Where does the string docker.example.com in my GitLab CI job come from?
mcnesium
# Where does the string docker.example.com in my GitLab CI job come from?

(Asked by: username_0 on 2021-08-31)

I am trying to have a Docker image deployed to my server by GitLab CI, but it only worked once¹ and then dies with the error message below. Here is the .gitlab-ci.yml snippet:
deploy-image:
  image: docker:latest
  services:
    - docker:dind
  variables:
    DOCKER_HOST: ssh://gitlab-ci@$DEPLOY_HOST
  before_script:
    - eval $(ssh-agent -s)
    - echo "${SSH_KEY}" | ssh-add -
    - mkdir -p ~/.ssh
    - '[[ -f /.dockerenv ]] && echo -e "Host *\n\tStrictHostKeyChecking no\n\n" > ~/.ssh/config'
  script:
    - echo $CI_JOB_TOKEN | docker login --username gitlab-ci-token --password-stdin $CI_REGISTRY;
    - docker pull "$CI_REGISTRY_IMAGE"
    - docker run --name mycontainer --detach $CI_REGISTRY_IMAGE
  after_script:
    - docker logout $CI_REGISTRY

The error in the job log looks like that:
Executing "step_script" stage of the job script 00:04
Using docker image sha256:51453dcdd9bd51e503f75e6d42a4071469ad2ba816321781985041b6bc7776db for docker:latest with digest docker@sha256:ddf0d732dcbc3e2087836e06e50cc97e21bfb002a49c7d0fe767f6c31e01d65f ...
$ eval $(ssh-agent -s)
Agent pid 18
$ echo "${SSH_KEY}" | ssh-add -
Identity added: (stdin) (gitlab-ci@jacks)
$ mkdir -p ~/.ssh
$ [[ -f /.dockerenv ]] && echo -e "Host *\n\tStrictHostKeyChecking no\n\n" > ~/.ssh/config
$ echo $CI_JOB_TOKEN | docker login --username gitlab-ci-token --password-stdin $CI_REGISTRY;
error during connect: Post "http://docker.example.com/v1.24/auth": command [ssh -l gitlab-ci -- xxx.xxx.xxx.xxx docker system dial-stdio] has exited with exit status 255, please make sure the URL is valid, and Docker 18.09 or later is installed on the remote host: stderr=ssh: connect to host xxx.xxx.xxx.xxx port 22: Connection refused

While I x-ed out the IP address of the destination server in this post (which is the value of the DEPLOY_HOST env var), it literally says docker.example.com in the error message.
So my question would be, where that example string comes from.
This is on a self-hosted GitLab instance and the runner is also self-hosted on a server that is neither the destination host, nor the one where GitLab runs on.
¹ The connection issue itself seems to be a problem with the SSH connection and not related to the CI/CD pipeline config.

**Tags:** docker, gitlab, deployment, cicd

> **Comments:**
> **username_1**: `Post "http://docker.example.com/v1.24/auth"` is likely coming from `docker login --username gitlab-ci-token --password-stdin $CI_REGISTRY;` - what's the value of $CI_REGISTRY  
> **username_0**: The value of `$CI_REGISTRY` is the container registry. It is a pre-defined variable that is specific to every project and defined automatically by GitLab CI, see https://docs.gitlab.com/ee/ci/variables/predefined_variables.html (sorry for answering late)  

---

## 1 answers

### Answer by username_2 on 2021-12-19. Score: 11 | Accepted answer

It's a placeholder domain name for connecting over SSH. It doesn't mean that it's connecting to docker.example.com.
I ran into a similar error when using a Docker client over SSH. The error message was:
ERROR: Cannot connect to the Docker daemon at http://docker.example.com. Is the docker daemon running?

Reading the Docker source code, it looks like "docker.example.com" is a placeholder host name when connecting over SSH, resulting in the confusing error message.
In my case, the error was caused by the user I was logging in as not being part of the docker group, and therefore not having permission to use docker.

> **Comments:**
> **username_0**: Thank you for investigating this. So do you think this behavior is unexpected and therefore worth reporting as a bug? I think it is at least misleading when the actual problem is something else.  
> **username_2**: @username_0 Yes, I think that's confusing enough to count as a bug. Also, here's another person who ran into the same problem: https://forums.docker.com/t/docker-compose-through-ssh-failing-and-referring-to-docker-example-com/115165  
> **username_2**: When I saw this, I was copy-pasting an example into my terminal, so I thought I must have forgotten to change some placeholder. Spent a bunch of time looking for where I forgot to replace 'docker.example.com.'  
> **username_3**: This can occur when you have a multi-platform buildx setup that includes a remote machine. I do it to do x86+arm64 builds from an M1 Mac, with a remote x86 box doing the cross-platform build while my M1 does the arm64 build in parallel, each doing their thing without emulation. If I don't have Docker up on the remote host, I get this error.  

---

