Monday, May 3, 2010

Adventures with chef-server and Gentoo, part 4

Continued from Part 3

When I followed the instructions for chef-overlay, I noticed a feature for Portage that I never knew existed. For those not familiar with Gentoo, you can specify fine-grained control over the exact version number of compile-time features with four files, /etc/portage/package.use, /etc/portage/package.keywords, /etc/portage/package.unmask, and /etc/portage/package.mask.

The official documentation shows using these as files. However, the instructions from chef-overlay shows that you can make those files as directories, and put multiple files in those directories. For example, instead of:


you can instead have,


I wish I had known about this years earlier. My old Gentoo laptop that I used for Rails development has been around since 2006, and has accrued a large set of use flags and keywords. (It is time to wipe that laptop clean and rebuild).

One cool thing about this setup is that autounmask will handle this layout gracefully. For example, if I were to autounmask =net-misc/rabbitmq-server-1.7.2-r2, it will create a file /etc/portage/package.keywords/autounmask-rabbitmq-server instead of attempting to inserting the change into the base /etc/portage/package.keywords ... which may have custom changes a human have made. Human-editable files would require the use of git to manage well. The files generated from autounmask can be added and removed atomically.

I'm not entirely sure this is still the way to go with a Gentoo + Chef infrastructure. Reading the paper, Why Order Matters: Turing Equivalence in Automated Systems Administration, one of the key things for congruent infrastructure is being able to rebuild at anytime. Does having it broken out like that make it easier? I think it is, but we will see.

I have pushed up a portage recipe that sets this up. I took some time to make sure that any legacy files gets backed up and moved into the new directory structure. Again, I'm not sure this is entirely a great idea since it tempts people to attempt to apply Chef, a congruence tool, on what is effectively a convergence problem. I'm leaving it there for now simply because the stem-cell images I am using had some of those files already in place (most notably, turning off the threads use flag for the ruby package).

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