The following guide is intended for those interested in the inner workings of nodepool and its various processes.
If you send a SIGUSR2 to one of the daemon processes, Nodepool will dump a stack trace for each running thread into its debug log. It is written under the log bucket nodepool.stack_dump. This is useful for tracking down deadlock or otherwise slow threads.
The following is the overall diagram for the nodepool-builder process and its most important pieces:
+-----------------+
| ZooKeeper |
+-----------------+
^ |
bld | | watch
+------------+ req | | trigger
| client +---------+ | +--------------------+
+------------+ | | NodepoolBuilderApp |
| +---+----------------+
| |
| | start/stop
| |
+-------v-------+ |
| <-------+
+---------> NodePool- <----------+
| +---+ Builder +---+ |
| | | | | |
| | +---------------+ | |
| | | |
done | | start start | | done
| | bld upld | |
| | | |
| | | |
+---------v---+ +---v----------+
| BuildWorker | | UploadWorker |
+-+-------------+ +-+--------------+
| BuildWorker | | UploadWorker |
+-+-------------+ +-+--------------+
| BuildWorker | | UploadWorker |
+-------------+ +--------------+