Use capistrano to run a remote rake task, with maintenance mode

So the app I am now working on is still in it’s early stages, not even live to the public yet, but we’ve got an internal server. We periodically have to change a bunch of data in our (non-rdbms) “production” store. (First devops unhappiness, I think there should be no scheduled downtime for planned data transformation. We’re working on it. But for now it happens).

We use capistrano to deploy. Previously/currently, the process for making these scheduled-downtime maintenance mode looked like:

  • on your workstation, do a cap production maintenance:enable to start some downtime
  • ssh into the production machine, cd to the cap-installed app, and run a bundle exec run a rake task. Which could take an hour+.
  • Remember to come back when it’s done and `cap production maintenance:disable`.

A couple more devops unhappiness points here: 1) In my opinion you should ideally never be ssh’ing to production, at least in a non-emergency situation.  2) You have to remember to come back and turn off maintenance mode — and if I start the task at 5pm to avoid disrupting internal stakeholders, I gotta come back after busines hours to do that! I also think every thing you have to do ‘outside business hours’ that’s not an emergency is a not yet done ops environment.

So I decided to try to fix this. Since the existing maintenance mode stuff was already done through capistrano, and I wanted to do it without a manual ssh to the production machine, capistrano seemed a reasonable tool. I found a plugin to execute rake via capistrano, but it didn’t do quite what I wanted, and it’s implementation was so simple that I saw no reason not to copy-and-paste it and just make it do just what I wanted.

I’m not gonna maintain this for the public at this point (make a gem/plugin out of it, nope), but I’ll give it to you in a gist if you want to use it. One of the tricky parts was figuring out how to get “streamed” output from cap, since my rake tasks use ruby-progressbar — it’s got decent non-TTY output already, and I wanted to see it live in my workstation console. I managed to do that! Although I never figured out how to get a cap recipe to require files from another location (I have no idea how I couldn’t make it work), so the custom class is ugly inlined in.

I also ordinarily want maintenance mode to be turned off even if the task fails, but still want a non-zero exit code in those cases (anticipating future further automation — really what I need is to be able to execute this all via cron/at too, so we can schedule downtime for the middle of the night without having to be up then).

Anyway here’s the gist of the cap recipe. This file goes in ./lib/capistrano/tasks in a local app, and now you’ve got these recipes. Any tips on how to organize my cap recipe better quite welcome.

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