This HTTP-based microservice offers a ReST API to acquire and release resources that are limited with a semaphore semantic.

Some software uses a global license server to checkout licenses while the software is executed. By default many license consumers (clients) fail and abort the execution if no valid license was found or if no license was free for a checkout. In such cases, a CI pipeline would also fail, because the job is failing caused by the license error. In many cases there are no retries nor waits for a license to become valid or available again. More over waiting time would be counted as job execution time.

This semaphore service allow to acquire a license virtually before asking the actual license server. If no license is available, it will either wait or register a callback for the real working job.

Application => WebServer     => HTTPInterface => Router => API => Semaphore => storage  
Daemon     / \ NGINX + WSGI /