some works can be combined with multiple components or at least multiple operation. I read through open stack code(actually neutron), but I can't find how open stack deal with error recovery. lets' assume some works needs operation A,B. the A succeed, but the B didn't, so it can cause that the redundant A remains in stack. I thought open stack will do some roll back operation to deal with these things. But it look like that it just print error log. Moreover it doesn't report back(couldn't find any rpc call) when they cause error. how open stack deal with these kinds of problem? Or what is the design decision for the error at long combined works?