Jenkins slave cannot connect with master: Incorrect acknowledgement sequence

Question

After update of our Jenkins master installation to its latest LTS version 2.46.3 one of its slaves (Windows 7 machine, 32-bit) cannot connect with the master.

The error we're getting is:

java -jar slave.jar -jnlpUrl https://<jenkins-name>/computer/<node-name>/slave-agent.jnlp -secret <secret-value>
Jun 22, 2017 1:19:05 PM hudson.remoting.jnlp.Main createEngine
INFO: Setting up slave: node-name
Jun 22, 2017 1:19:05 PM hudson.remoting.jnlp.Main$CuiListener <init>
INFO: Jenkins agent is running in headless mode.
Jun 22, 2017 1:19:05 PM hudson.remoting.jnlp.Main$CuiListener status
INFO: Locating server among [https://<jenkins-name>/]
Jun 22, 2017 1:19:05 PM org.jenkinsci.remoting.engine.JnlpAgentEndpointResolver resolve
INFO: Remoting server accepts the following protocols: [JNLP3-connect, JNLP-connect, CLI2-connect, Ping, CLI-connect, JNLP4-connect, JNLP2-c
onnect]
Jun 22, 2017 1:19:05 PM hudson.remoting.jnlp.Main$CuiListener status
INFO: Agent discovery successful
  Agent address: <jenkins-name>
  Agent port:    <jenkins-port>
  Identity:      <id:en:ti:ty>
Jun 22, 2017 1:19:05 PM hudson.remoting.jnlp.Main$CuiListener status
INFO: Handshaking
Jun 22, 2017 1:19:05 PM hudson.remoting.jnlp.Main$CuiListener status
INFO: Connecting to <jenkins-name>:9150
Jun 22, 2017 1:19:05 PM hudson.remoting.jnlp.Main$CuiListener status
INFO: Trying protocol: JNLP4-connect
Jun 22, 2017 1:19:05 PM org.jenkinsci.remoting.protocol.impl.AckFilterLayer abort
WARNING: [JNLP4-connect connection to <our-proxy>/10.253.0.11:81] Incorrect acknowledgement sequence, expected 0x0003414333 got 0x4854545044
Jun 22, 2017 1:19:05 PM hudson.remoting.jnlp.Main$CuiListener status
INFO: Protocol JNLP4-connect encountered an unexpected exception
java.util.concurrent.ExecutionException: org.jenkinsci.remoting.protocol.impl.ConnectionRefusalException: Connection closed before acknowled
gement sent
        at org.jenkinsci.remoting.util.SettableFuture.get(SettableFuture.java:223)
        at hudson.remoting.Engine.innerRun(Engine.java:385)
        at hudson.remoting.Engine.run(Engine.java:287)
Caused by: org.jenkinsci.remoting.protocol.impl.ConnectionRefusalException: Connection closed before acknowledgement sent
        at org.jenkinsci.remoting.protocol.impl.AckFilterLayer.onRecvClosed(AckFilterLayer.java:280)
        at org.jenkinsci.remoting.protocol.FilterLayer.abort(FilterLayer.java:164)
        at org.jenkinsci.remoting.protocol.impl.AckFilterLayer.abort(AckFilterLayer.java:130)
        at org.jenkinsci.remoting.protocol.impl.AckFilterLayer.onRecv(AckFilterLayer.java:258)
        at org.jenkinsci.remoting.protocol.ProtocolStack$Ptr.onRecv(ProtocolStack.java:669)
        at org.jenkinsci.remoting.protocol.NetworkLayer.onRead(NetworkLayer.java:136)
        at org.jenkinsci.remoting.protocol.impl.BIONetworkLayer.access$2200(BIONetworkLayer.java:48)

We spent a lot of time trying to fix the problem. Unfortunately without success.

Do you have an idea what could have caused the problem and how can it be solved?

Answer 1

We recently hit this issue with our AWS-based Jenkins using JNLP for remote integration testing. The remote slave would call back to the Jenkins master, which failed with a similar error. The issue ended up being a dynamically generated AWS ELB of type HTTP (because the Kubernetes ELB provisioner presently doesn't support multi-protocol ELBs) for the Jenkins Master. We had to manually change the JNLP ingress port type of the ELB to TCP, while the web interface ingress 'instance port' was protocol HTTP and 'load balancer' was protocol HTTPS.