Connection refused when connecting to Docker SSH agent

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1

I’ve followed this guide on how to create a Jenkins agent using Docker and SSH, and have not been able to get it working. I’ve followed the steps on this page in full twice now, and no matter what I do I always get the following output on my agent:

SSHLauncher{host='localhost', port=4445, credentialsId='jenkins-ssh', jvmOptions='', javaPath='', prefixStartSlaveCmd='', suffixStartSlaveCmd='', launchTimeoutSeconds=60, maxNumRetries=10, retryWaitTime=15, sshHostKeyVerificationStrategy=hudson.plugins.sshslaves.verifiers.ManuallyTrustedKeyVerificationStrategy, tcpNoDelay=true, trackCredentials=true}
[11/15/24 01:21:17] [SSH] Opening SSH connection to localhost:4445.
Connection refused
SSH Connection failed with IOException: "Connection refused", retrying in 15 seconds. There are 10 more retries left.

I tried with the default port of 22, as well as with custom ports of 4444 and 4445, neither of which yielded a different result. I also can’t find anyone online who is having the same issue as me.

Does anyone know what I’m doing wrong?

Jenkins setup:
Jenkins: 2.479.1
OS: Linux - 6.10.11-linuxkit
Java: 17.0.13 - Eclipse Adoptium (OpenJDK 64-Bit Server VM)

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2

Unfortunately, you didn’t link to the guide that you followed. It is easier for others if they can use the steps that you used.

I started a docker ssh agent process using the command line from the documentation like this:

docker run -d --rm --name=agent \
    --publish 2200:22 \
    -e "JENKINS_AGENT_SSH_PUBKEY=ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIHoGWb80kSBywPtvWbgeng7itaw7Tu6d/nXaxIKTQ05Z" \
    jenkins/ssh-agent

I configured the agent in my Jenkins controller to:

  • use host testing-b.markwaite.net
  • use port 2200 instead of the default port 22
  • use a credential that was the private key associated with the public key that is listed on the docker run command line
  • use /home/jenkins/agent as the home directory

Note that I initially had surrounded the public key with single quotes in order to retain the space that is part of the public key argument, but I had to remove those single quotes after reading the documentation page.

3

Hi, first apologies on forgetting the link, I have updated the post.

Second, I followed your steps and I’m still getting “Connection refused”. Some things:

  • I’m trying to connect to a Docker SSH agent that is running on my local computer (so everything here is ‘localhost’).
  • I tried with port 2200, didn’t change things.
  • I’m using the correct public key/private key pair.
  • I’m setting home directory as /home/jenkins/agent like you said. This, by the way, is not what the guide says, it says to just use /home/jenkins. I had to reference the documentation for the agent image to figure this out.
  • I prepare my commands in another text editor, and then copy-paste the entire command over to the Docker console. The agent container did not have issues starting up.
  • Below is the output for the log for my agent container:
2024-11-15 13:44:22 + [[ ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIPpMwzAcZBsJ2Poykbz0JXBApbcpwXnK7LwXZ1uXVQ09 == ssh-* ]]
2024-11-15 13:44:22 + write_key 'ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIPpMwzAcZBsJ2Poykbz0JXBApbcpwXnK7LwXZ1uXVQ09'
2024-11-15 13:44:22 + local ID_GROUP
2024-11-15 13:44:22 ++ stat -c %U:%G /home/jenkins
2024-11-15 13:44:22 + ID_GROUP=jenkins:jenkins
2024-11-15 13:44:22 + mkdir -p /home/jenkins/.ssh
2024-11-15 13:44:22 + echo 'ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIPpMwzAcZBsJ2Poykbz0JXBApbcpwXnK7LwXZ1uXVQ09'
2024-11-15 13:44:22 + chown -Rf jenkins:jenkins /home/jenkins/.ssh
2024-11-15 13:44:22 + chmod 0700 -R /home/jenkins/.ssh
2024-11-15 13:44:22 + [[ '' == ssh-* ]]
2024-11-15 13:44:22 + env
2024-11-15 13:44:22 + grep _
2024-11-15 13:44:22 + [[ 0 -gt 0 ]]
2024-11-15 13:44:22 + ssh-keygen -A
2024-11-15 13:44:22 + exec /usr/sbin/sshd -D -e
2024-11-15 13:44:22 Server listening on 0.0.0.0 port 22.
2024-11-15 13:44:22 Server listening on :: port 22.
2024-11-15 13:44:22 ssh-keygen: generating new host keys: RSA ECDSA ED25519

I can confirm that the public key shown here is correct and what is included in my ssh creds.

EDIT: Additionally here is the command I used to start up my container:

docker run -d --rm --name=agent1 -p 2200:22 \
-e "JENKINS_AGENT_SSH_PUBKEY=ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIPpMwzAcZBsJ2Poykbz0JXBApbcpwXnK7LwXZ1uXVQ09" \
jenkins/ssh-agent:alpine-jdk17