Failure to deliver XID in Seata distributed transaction project

Recently seata Encountered in the project xid Unable to get feign Transfer to other micro Services . I found information on the Internet solve seata stay Fegin Open fuse （Hystrix） Transactions cannot be passed between microservices XID Problems and non delivery oauth2 token Problem compatibility Zipkin, Because the article doesn't mention the most important place , So I haven't found the problem yet .

So interrupt point tracking , See that the current service has xid Of , But by feign Invocation time ,xid It's gone , It's weird . Restart the service again and debug, Still the same . I've been tossing around for a long time without making progress . I think of , Since the current service has xid, after feign It's gone when , So is the middle After the destruction steps ？ So in RootContext Inside , to unbind Method to hit a breakpoint , And then something magical happened ： After the current service, there are xid,SeataFeignClient There is no xid After the steps ,unbind See again xid 了 .

The magic lies in , Why? unbind The step is to feign What happens after the call ？ Since it was untied later , that feign Why is there no such thing in xid Well ？ I think there is only one explanation ： Get twice xid Not in the same context .
So I told the big guys around me , At this time, he finally gave the answer to the question ：hystrix There are two service isolation modes ： Thread pool isolation and semaphore isolation , Thread pool isolation is used by default . This leads to the call feign Different threads are used , So we can't get the in the previous thread xid. That's easy , take hystrix Change the service isolation mode to semaphore isolation . Call again , Finally got it .

So far, the matter has come to an end .

Think about something else you can learn from .
For example, I found feign Can't get xid, It still took a lot of time to debug, To track , But still nothing . In fact, from here, we can basically conclude that , This road won't work , We should change our thinking . And I spent a lot of time getting nothing , I suddenly thought of other ways . This is an unconscious , A very passive process , Resulting in inefficiency . So I got an experience —— That the road is blocked , Change your mind now .
Another lesson is , Have rich knowledge accumulation . I found unbind You can see xid, In fact, we are very close to finding the answer , It's like digging a well , Dig a few more shovels and you'll get out of the water . But I don't know yet Hystrix Thread pool and semaphore are two isolation modes , So it's a little different from the truth .

All in all , The above is an interesting process . Therefore, there is this article. .