Unable to run jenkins build inside a docker agent using SSH connection method

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You’ve not provided enough details so that others can duplicate your configuration. The details you’ve provided are using an unmaintained container image. Assisting without enough information is a frustrating experience for those who try to assist. Please provide clear steps of the exact changes you made so that others can duplicate your configuration exactly.

I took the following steps to confirm that I can use the jenkins/ssh-agent:5.22.0-alpine3.19-jdk21 container image with Jenkins 2.426.2 running with Java 21.

  1. I added an ED 25519 SSH private key to my Jenkins 2.426.2 controller running with Java 21 and then on another machine, called “testing-b”, I started the ssh-agent container image listening on port 2200 and using the ssh public key like this:
docker run -d --rm --name=agent \
    --publish 2200:22 \
    -e "JENKINS_AGENT_SSH_PUBKEY=ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIHoGWb80kSBywPtvWbgeng7itaw7Tu6d/nXaxIKTQ05Z" \
    jenkins/ssh-agent:5.22.0-alpine3.19-jdk21
  1. I added the ssh private key associated with that ED25519 public key to my Jenkins 2.426.2 controller as a credential for the user “jenkins”
  2. I configured a Jenkins agent on my Jenkins 2.426.2 controller with the agent home directory “/home/jenkins/agent”, the hostname “testing-b”, and the port 2200
  3. I clicked “Launch agent” and confirmed that the agent connected correctly

I did not use the docker plugin to control that agent because I did not want the added complexity of configuring a network accessible docker daemon. Using a static agent is enough to show that the authentication works and the agent is connected.