I am configuring a permanent ssh agent in a Jenkins pod that runs on an Openshift cluster and for that purpose I inject the private ssh key from an openshift secret.

When I deploy the jenkins pod, the ssh agent does not manage to start. The error message is:

[09/30/19 08:48:54] [SSH] Opening SSH connection to ${server-adress}:22.
[09/30/19 08:48:56] [SSH] SSH host key matches key seen previously for this host. Connection will be allowed.
ERROR: Server rejected the 1 private key(s) for jenkins
 (credentialId:project-ssh-agent/method:publickey)
[09/30/19 08:48:56] [SSH] Authentication failed.
Authentication failed.
[09/30/19 08:48:56] Launch failed - cleaning up connection
[09/30/19 08:48:56] [SSH] Connection closed. 

In order to get the connection working, I go to the credentials store in the Jenkins UI https://${jenkins-url}/credentials/store/system/domain/_/credential/project-ssh-agent/update, go to Update credentials and click on Save without having changed anything about the credentials.

Clicking on relaunch agent now spawns the agent using the ssh connection to connect to the remote server as configured.

Considerations

The injection works fine and the resulting ssh-key in the Jenkins credentials store can directly be used for ssh-based git checkouts. I previously had opened a ticket about this with the openshift jenkins-sync-plugin support (https://github.com/openshift/jenkins-sync-plugin/issues/345).