Delegated Builds

Introduction

I cooked up something at work that I think is going to be awesome for building the project that I work on a day to day basis. Here's the basic problem, in a different post, I'll expand on these in more depth:

  • we do continuous deployment.
  • we maintain and publish multiple branches.
  • our builds take a non-trivial amount of time (4-6 minutes depending on hardware,) and will continue to get longer.
  • our documentation toolkit, Sphinx, lacks concurrency for some steps, which means builds take too long and leave most of a contemporary computer idle. Furthermore, given our use of topic-branches it can be hard to get work done during a build.

So there are a couple of notable hacks that I've come up with, over the past few months that help:

  • duplicate some of the initial work so that different output formats can build in parallel (using Make's job control) at the expense of disk some space.
  • using a source proxy, (i.e. copying the source content into the build directory and building from this copy so that the actual source files can change during the build.)

These changes are simple and amount to some really minor changes to commands and Make files. This next fix required a non-trivial amount of code, but is really awesome:

  • building content, if it's already committed, from a local checkout in the build directory. This way you can build (and publish!) from a different branch without doing anything to your current working directory.

The Code

See the gist for a basic overview, and keep your eyes on the repositories:

Some implementation notes:

  • it needs a bit more clean up and configuration with regards to a few hard-coded directory names, and assumptions about projects.

  • in practice it should work fine with Python 2.7 and 3.0. If you have the backported argparse module for 2.6, that should work too.

  • this plugs in really nicely with some existing infrastructure: becasuse we generate most of our Makefiles, it's trivial to make this script smart and only permit sane things with regards to branch creation/management, and build targets.

    Building on this, I've written up a separate script to generate makefile targets to invoke these commands, which allows the script to fit more nicely into the existing idiom. That's not included here, yet.

  • this, so far, has been the best introduction I've gotten to the subprocess module, so perhaps this will be useful to you.

  • there's no good way to queue builds in make, except to use the blocking mode and use a bunch of make calls, which is reasonably inefficient. To get better at this, we'll need to make some underlying build changes, but the gains could be pretty significant.

  • finally, this is the first bit of Python I've written since I had the breakthrough where I finally understood classes of a moderate amount of complexity without classes. No harm, and it's not like there's any internal state; at the same time, a bit of encapsulation around the interactions with git might be useful.

Pull request, suggestions, are always welcome.

More On Delegated Builds

I've written a bunch more about this problem and script and will be posting some of that very soon!

(Also it's good to return to blogging/posting. Thanks for sticking around!)

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