could configure jenkins slave in docker container from jenkins server in docker - docker

Question

I'm practicing docker in practice by manning.
The technical recipe is about configuring jenkins slave which is docker container.
Below is the Dockerfile for jenkins_slave
FROM ubuntu:latest
ENV DEBIAN_FRONTEND noninteractive
RUN groupadd -g 1000 jenkins_slave
RUN useradd -d /home/jenkins_slave -s /bin/bash \
-m jenkins_slave -u 1000 -g jenkins_slave
RUN echo jenkins_slave:jpass | chpasswd
RUN apt-get update && \
apt-get install -y openssh-server openjdk-8-jre wget iproute2
RUN mkdir -p /var/run/sshd
CMD ip route | grep "default via" \
| awk '{print $3}' && /usr/sbin/sshd -D
I built docker images using the command
docker build -t jenkins_slave .
Then I run the docker images as container using the command
$ docker run --name jenkins_slave -it -p 2222:22 jenkins_slave
172.17.0.1
Then I run the jenkins server using the below docker command
$ docker run --name jenkins_server -p 8080:8080 -p 50000:50000 dockerinpractice/jenkins:server
Below is the node configuration details -
Then I get the error message saying This agent is offline because Jenkins failed to launch the agent process on it
Below is the error stack trace
[12/07/17 08:50:00] [SSH] Opening SSH connection to 172.17.0.1:2222.
/var/jenkins_home/.ssh/known_hosts [SSH] No Known Hosts file was found at
/var/jenkins_home/.ssh/known_hosts. Please ensure one is created at this path and that Jenkins can read it.
Key exchange was not finished, connection is closed.
java.io.IOException: There was a problem while connecting to 172.17.0.1:2222
at com.trilead.ssh2.Connection.connect(Connection.java:834)
at com.trilead.ssh2.Connection.connect(Connection.java:703)
at com.trilead.ssh2.Connection.connect(Connection.java:617)
at hudson.plugins.sshslaves.SSHLauncher.openConnection(SSHLauncher.java:1284)
at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:804)
at hudson.plugins.sshslaves.SSHLauncher$2.call(SSHLauncher.java:793)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.io.IOException: Key exchange was not finished, connection is closed.
at com.trilead.ssh2.transport.KexManager.getOrWaitForConnectionInfo(KexManager.java:95)
at com.trilead.ssh2.transport.TransportManager.getConnectionInfo(TransportManager.java:237)
at com.trilead.ssh2.Connection.connect(Connection.java:786)
... 9 more
Caused by: java.io.IOException: The server hostkey was not accepted by the verifier callback
at com.trilead.ssh2.transport.KexManager.handleMessage(KexManager.java:548)
at com.trilead.ssh2.transport.TransportManager.receiveLoop(TransportManager.java:790)
at com.trilead.ssh2.transport.TransportManager$1.run(TransportManager.java:502)
... 1 more
I have a simple build configuration called test but the build is not running since the slave is offline.
Any idea why the jenkins master is not identifying the slave server.

Answer 1

Just change the Host Key verification strategy to Non verfiying Verification Strategy in the node configuration.

Answer 2

You are using Host Key verification strategy method which checks the known_hosts file ( usually it's at ~/.ssh/known_hosts). However the jenkins server is checking /var/jenkins_home/.ssh/known_hosts, which probably is empty now, in the docker container.
You can use Manually provided key Verification Strategy and paste the public key there or using other methods with the help of this document.