Jenkins controller fails to connect to the agent over SSH

Question

Jenkins controller is running on Amazon instance and agent machine set up on dedicated Soyoustart machine. Worked fine until it was needed to redo the agent setup: reinstalled the OS, installed Java, added controllers key to agent's authorized_keys and removed/added again the agent in the controller's known_hosts. Set up new credentials for the agent and configured the node in Jenkins controller, but it is unable to connect to the agent.

The setup is the the same that is and has been working with other agents without hiccups. The only thing different is that this time the new agent is the same machine with the IP as the old one was.

It is possible to ssh into the agent machine from controller machine from CLI(replaced filename and agent IP with placeholder for this post): $ ssh -i <key-file> jenkins@<agent-ip>

Credentials have been set up :

Node is configured:

Output when connecting to the agent:

[05/17/15 07:30:31] [SSH] Opening SSH connection to <agent-ip>.
Key exchange was not finished, connection is closed.
ERROR: Unexpected error in launching a slave. This is probably a bug in Jenkins.
java.lang.IllegalStateException: Connection is not established!
at com.trilead.ssh2.Connection.getRemainingAuthMethods(Connection.java:1030)
at com.cloudbees.jenkins.plugins.sshcredentials.impl.TrileadSSHPublicKeyAuthenticator.getRemainingAuthMethods(TrileadSSHPublicKeyAuthenticator.java:88)
at com.cloudbees.jenkins.plugins.sshcredentials.impl.TrileadSSHPublicKeyAuthenticator.canAuthenticate(TrileadSSHPublicKeyAuthenticator.java:80)
at com.cloudbees.jenkins.plugins.sshcredentials.SSHAuthenticator.newInstance(SSHAuthenticator.java:207)
at com.cloudbees.jenkins.plugins.sshcredentials.SSHAuthenticator.newInstance(SSHAuthenticator.java:169)
at hudson.plugins.sshslaves.SSHLauncher.openConnection(SSHLauncher.java:1173)
at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:701)
at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:696)
at java.util.concurrent.FutureTask.run(FutureTask.java:262)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
[05/17/15 07:30:31] Launch failed - cleaning up connection
[05/17/15 07:30:31] [SSH] Connection closed.

Version numbers:

• Jenkins 1.613
• SSH Credentials Plugin 1.11
• SSH Slaves plugin 1.9

For those who prefer to dig into code:

• SSH Credentials Plugin

• SSH Slave Plugin

• Trilead SSH

Am I missing something obvious here? What could be causing this? Any known workaround? Or does it look like a bug that needs to be reported?

Please let me know if more information is needed.

Kenning

I've encounter the exact same issue. Have you fix it? I'm using the Jenkins 2.46.1. – Outclass

Never resolved this one. I just ended up not using that particular slave. – Kenning

Does the issue shows on this particular slave or all of Mac environment? – Outclass

Answer 1

I'm running Jenkins master using official Docker image which uses OpenJDK8 and should not need to install JCE.

Apparently this is an unresolved issue in Jenkins/SSH security.

My current workaround is by commenting out MACs and KexAlgorithm line in /etc/ssh/sshd_config of Jenkins Slave and restarting the sshd (service ssh restart on Ubuntu)

---

UPDATE: the issue has been resolved as of 2017-04-29

Martell

Answer 2

I suspect that you need to install the Java Cryptography Extension for your JVM. Without that the RSA key size is limited and authentication is not being established.

See https://issues.jenkins-ci.org/browse/JENKINS-26495 for more details.

Candancecandela

You probably missed the part where I said that it connects fine to other slaves. – Kenning

@TanelMae I got the exact same issue too. I'm running Jenkins using official Docker image which uses OpenJDK8 and don't need to install JCE – Martell