Analysis of port 9848 error at startup of Nacos client (non-version upgrade problem)

I. Background

Many people will report the following error when the Nacos client is started, indicating that the connection to port 9848 has timed out.

I also searched for it myself, and many articles said that it was a version problem. It would be good to upgrade the client to 2.0, but I found that many people still report this error after upgrading.Well, there is no answer on the Internet, so I can only analyze it myself.

Second, analyzing the source code

Find the place where the error is reported GrpcClient.serverCheck() method, then break the point, restart, wait for the following line to be executed, and find that the error is not reported again, and then the startup is successful!

responseFuture.get(3000L, TimeUnit.MILLISECONDS);

After several attempts, no error will be reported as long as the breakpoint is interrupted, and an error will be reported if the breakpoint is not interrupted.

After careful study, requestBlockingStub.request is a non-blocking request, and directly enters after the request

responseFuture.get(3000L, TimeUnit.MILLISECONDS) In the method, this method is to judge whether the above request response is returned. You can look at the logic inside, generally within the 3-second timeout period, it will loop to determine whether the response isReturn, if the timeout does not return, an exception will be thrown.

This is why after hitting the breakpoint, no error will be reported. Hitting the breakpoint will invisibly increase the timeout period. Before judging the timeout method, the response has been returned, and naturally no error will be reported.

Third, whether the startup is successful

Most people, after the error is reported at startup, the project is still successfully started, and the nocas service list is already available, but they are still a little confused when they see the error. Is it really okay?Let's analyze it again, find the source, and report the error method serverCheck, where did it start to call

Follow step by step, find the connectToServer method of this class

Continue to find the place to call the connectToServer method and locate the start method in RpcClient.class

I found that when connectToServer is called, it returns null (that is, it returns null after the previous error is reported), it willRetry three times, generally the connection will be successful the second time, and it will print out Success to connect to serveron start up

So after you start the error report, see if there is a success log below the error log. If there is a success log, it means that it is normal and there is no problem.

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