When is it not cool to add a new OpenStack configuration option?

Adding new configuration options has a cost, and makes already complex projects (Hi Neutron!) even more so. Double so when we speak of architecture choices, it means that we have to test and document all permutations. Of course, we don’t always do that, nor do we test all interactions between deployment options and other advanced features, leaving users with fun surprises. With some projects seeing an increased rotation of contributors, we’re seeing wastelands of unmaintained code behind left behind, increasing the importance of being strategic about introducing new complexity.

I categorize the introduction of new OpenStack configuration options to two:

  1. There’s two or more classes of operators that have legitimate use cases and a configuration option would enable those use cases without hurting cloud interoperability
    • For example: Neutron DVR, is essentially a driver for router implementations, that changes your L3 architecture substantially while abstracting details via an API. DVR has various costs and benefits and letting operators make that choice, especially as the feature matures, makes sense to me.
  2. Developers that don’t fully understand the choice they are making and pass the complexity down to the operators to figure out. This results in options that are often never changed from their defaults because operators don’t have access to sufficient documentation that explains the rationale for choosing a specific value, as well as a misuse of time and energy because developers sometimes focus on use cases that are off center or don’t exist.
    • For example: neutron.conf:DEFAULT:send_events_interval: Number of seconds between sending events to nova if there are any events to send. Unless you grep through the code, how is an operator supposed to know if they should increase or decrease the value? Even then, shouldn’t developers take responsibility of that choice, and test for the best value? If problems are found under load, shouldn’t the value be calculated as a function of some variable? Instead of distributing the work to thousands of operators, wouldn’t we as a community like to to do the work in one place?

When contemplating adding a new option, ask yourself:

  1. Is it possible that you don’t fully understand the use case, and in lieu of making a choice, you’re letting the operator bear the burden?
  2. Are you, and your replacement, prepared to own the cost of the new option indefinitely?

One thought on “When is it not cool to add a new OpenStack configuration option?

  1. Pingback: Recent blog posts – May 22nd – GREENSTACK

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