今天遇到特别狗血的一个问题，配置了从节点之后，下载了jar包到slave的服务器上运行指定的命令，竟然报错了

java.util.concurrent.ExecutionException: org.jenkinsci.remoting.protocol.impl.ConnectionRefusalException: Connection closed before acknowledgement sent

at org.jenkinsci.remoting.util.SettableFuture.get(SettableFuture.java:223)

at hudson.remoting.Engine.innerRun(Engine.java:743)

at hudson.remoting.Engine.run(Engine.java:518)

Caused by: org.jenkinsci.remoting.protocol.impl.ConnectionRefusalException: Connection closed before acknowledgement sent

at org.jenkinsci.remoting.protocol.impl.AckFilterLayer.onRecvClosed(AckFilterLayer.java:283)

at org.jenkinsci.remoting.protocol.FilterLayer.abort(FilterLayer.java:164)

at org.jenkinsci.remoting.protocol.impl.AckFilterLayer.access$000(AckFilterLayer.java:45)

at org.jenkinsci.remoting.protocol.impl.AckFilterLayer$1.run(AckFilterLayer.java:179)

at org.jenkinsci.remoting.protocol.IOHub$DelayedRunnable.run(IOHub.java:964)

at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)

at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)

at hudson.remoting.Engine$1.lambda$newThread$0(Engine.java:117)

at java.base/java.lang.Thread.run(Thread.java:844)

5月 25, 2020 8:13:51 下午 hudson.remoting.jnlp.Main$CuiListener error

严重: The server rejected the connection: None of the protocols were accepted

java.lang.Exception: The server rejected the connection: None of the protocols were accepted

at hudson.remoting.Engine.onConnectionRejected(Engine.java:828)

at hudson.remoting.Engine.innerRun(Engine.java:768)

at hudson.remoting.Engine.run(Engine.java:518)

去网上找了很多帮助，都没有用。突然灵光乍现，是不是master没有配置hosts所以无法访问啊。

于是加了hosts，重新执行，ok了！！！

折腾一晚上，终于好了。。。。记录一下，没准帮到其他人了呢。