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Cotyledon provides a framework for defining long-running services.

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Cotyledon provides a framework for defining long-running services.

It provides handling of Unix signals, spawning of workers, supervision of children processes, daemon reloading, sd-notify, rate limiting for worker spawning, and more.

Why Cotyledon

This library is mainly used in OpenStack Telemetry projects, in replacement of oslo.service. However, as oslo.service depends on eventlet, a different library was needed for project that do not need it. When an application do not monkeypatch the Python standard library anymore, greenlets do not in timely fashion. That made other libraries such as Tooz or oslo.messaging to fail with e.g. their heartbeat systems. Also, processes would not exist as expected due to greenpipes never being processed.

oslo.service is actually written on top of eventlet to provide two main features:

  • periodic tasks
  • workers processes management

The first feature was replaced by another library called futurist and the second feature is superseded by Cotyledon.

Unlike oslo.service, Cotyledon have:

  • The same code path when workers=1 and workers>=2
  • Reload API (on SIGHUP) hooks work in case of you don’t want to restarting children
  • A separated API for children process termination and for master process termination
  • Seatbelt to ensure only one service workers manager run at a time.
  • Is signal concurrency safe.
  • Support non posix platform, because it’s built on top of multiprocessing module instead of os.fork
  • Provide functional testing

And doesn’t:

  • facilitate the creation of wsgi application (sockets sharing between parent and children process). Because too many wsgi webserver already exists.

oslo.service being impossible to fix and bringing an heavy dependency on eventlet, Cotyledon appeared.

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