title: Kubernetes jenkins agent fails & shows - tcpSlaveAgentListener
body: <p>I am running<code>Jenkins Master</code> &amp; <code>K8s-Master</code> on same server. Jenkins running through tomcat Apache(not on K8s cluster). I have another server for <code>K8s-Worker-Node</code>, On both the server <code>CentOS-8</code> OS installed. I have configured <code>Jenkins Kubernetes Plugin version - 1.26.4</code> But while running pipeline job i always getting an error, Below is K8s cluster Jenkins agent pod log.</p>
  <pre><code>[root@K8s-Master /]# kubectl logs -f pipeline-test-33-sj6tl-r0clh-g559d -c jnlp
  
  Aug 08, 2020 8:37:21 AM hudson.remoting.jnlp.Main createEngine
  INFO: Setting up agent: pipeline-test-33-sj6tl-r0clh-g559d
  Aug 08, 2020 8:37:21 AM hudson.remoting.jnlp.Main$CuiListener &lt;init&gt;
  INFO: Jenkins agent is running in headless mode.
  Aug 08, 2020 8:37:21 AM hudson.remoting.Engine startEngine
  INFO: Using Remoting version: 4.3
  Aug 08, 2020 8:37:21 AM org.jenkinsci.remoting.engine.WorkDirManager initializeWorkDir
  INFO: Using /home/jenkins/agent/remoting as a remoting work directory
  Aug 08, 2020 8:37:21 AM org.jenkinsci.remoting.engine.WorkDirManager setupLogging
  INFO: Both error and output logs will be printed to /home/jenkins/agent/remoting
  Aug 08, 2020 8:37:21 AM hudson.remoting.jnlp.Main$CuiListener status
  INFO: Locating server among [http://jenkins-serverjenkins/]
  Aug 08, 2020 8:37:41 AM hudson.remoting.jnlp.Main$CuiListener error
  SEVERE: Failed to connect to http://jenkins-server/jenkins/tcpSlaveAgentListener/: jenkins-server
  java.io.IOException: Failed to connect to http://jenkins-serverjenkins/tcpSlaveAgentListener/: jenkins-server
          at org.jenkinsci.remoting.engine.JnlpAgentEndpointResolver.resolve(JnlpAgentEndpointResolver.java:217)
          at hudson.remoting.Engine.innerRun(Engine.java:693)
          at hudson.remoting.Engine.run(Engine.java:518)
  Caused by: java.net.UnknownHostException: jenkins-server
          at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184)
          at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
          at java.net.Socket.connect(Socket.java:607)
          at sun.net.NetworkClient.doConnect(NetworkClient.java:175)
          at sun.net.www.http.HttpClient.openServer(HttpClient.java:463)
          at sun.net.www.http.HttpClient.openServer(HttpClient.java:558)
          at sun.net.www.http.HttpClient.&lt;init&gt;(HttpClient.java:242)
          at sun.net.www.http.HttpClient.New(HttpClient.java:339)
          at sun.net.www.http.HttpClient.New(HttpClient.java:357)
          at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:1226)
          at sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1162)
          at sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1056)
          at sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:990)
          at org.jenkinsci.remoting.engine.JnlpAgentEndpointResolver.resolve(JnlpAgentEndpointResolver.java:214)
          ... 2 more
  </code></pre>
  <p>Below settings configuration already enabled.</p>
  <pre><code>Manage Jenkins --&gt; Configure Global Security --&gt; Agents Random [Enabled]
   
  </code></pre>
  <p><a href="https://i.stack.imgur.com/npvf4.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/npvf4.png" alt="enter image description here" /></a></p>
  <p>I am successfully able to communicate from my Jenkins to the K8s master cluster(Verified in Jenkins Cloud section).</p>
  <p>Even in K8s master all the namespace pods are running. <code>weave-net</code> CNI installed, Don't know what is causing problem while agent provisioning through Jenkins.</p>
  <p>My Jenkins/K8s master &amp; K8s-Worker-Node <code>/etc/hosts</code> as follows.</p>
  <pre><code># cat /etc/hosts
  127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
  ::1         localhost localhost.localdomain localhost6 localhost6.localdomain6
  
  75.76.77.5  jenkins-server jenkins-server.company.domain.com
  75.76.77.6  k8s-node-1 k8s-node-1.company.domain.com
  </code></pre>
  <p>Below output getting in K8s-Worker node. It looks there is no problem in connecting jenkins-master from K8s-worker node.</p>
  <pre><code>#  curl -I http://jenkins-server/jenkins/tcpSlaveAgentListener/
  HTTP/1.1 200
  Server: nginx/1.14.1
  Date: Fri, 28 Aug 2020 06:13:34 GMT
  Content-Type: text/plain;charset=UTF-8
  Connection: keep-alive
  Cache-Control: private
  Expires: Thu, 01 Jan 1970 00:00:00 GMT
  X-Content-Type-Options: nosniff
  X-Hudson-JNLP-Port: 40021
  X-Jenkins-JNLP-Port: 40021
  X-Instance-Identity: MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAnkgz8Av2x8R9R2KZDzWm1K11O01r7VDikW48rCNQlgw/pUeNSPJu9pv7kH884tOE65GkMepNdtJcOFQFtY1qZ0sr5y4GF5TOc7+U/TqfwULt60r7OQlKcrsQx/jJkF0xLjR+xaJ64WKnbsl0AiZhd8/ynk02UxFXKcgwkEP2PGpGyQ1ps5t/yj6ueFiPAHX2ssK8aI7ynVbf3YyVrtFOlqhnTy11mJFoLAZnpjYRCJsrX5z/xciVq5c2XmEikLzMpjFl0YBAsDo7JL4eBUwiBr64HPcSKrsBBB9oPE4oI6GkYUCAni8uOLfzoNr9B1eImaETYSdVPdSKW/ez/OeHjQIDAQAB
  X-Jenkins-Agent-Protocols: JNLP4-connect, Ping
  X-Remoting-Minimum-Version: 3.14
  
  # curl http://jenkins-server:40021/
  Jenkins-Agent-Protocols: JNLP4-connect, Ping
  Jenkins-Version: 2.235.3
  Jenkins-Session: 4455fd45
  Client: 75.76.77.6
  Server: 75.76.77.5
  Remoting-Minimum-Version: 3.14
  </code></pre>
  <p>It looks Kubernetes DNS not resolving the name. So any pointers to resolve this problem will help. Thanks.</p>