Enable mainenance mode only if there are pending migrations

[knwang]

I think this would be a good default. Currently paratrooper enables maintenance mode by default which causes about 3 minutes downtime, quite significant for typically production apps that can see several deploys a day.

Maintenance mode is mostly to ensure code/db consistency... so I propose that if there are no pending migrations, we can set the maintenance mode to false. Users can always use override this, of course.

Code change should be fairly simple.. if you are interested I can submit a PR ;)

[mattpolito]

Maintenance mode is enabled so the site doesn't get hit while code is being deployed. If the request even goes through, I would expect it to fail anyway because the instance would have to be restarted anyway. The flip of maintenance mode is almost instantaneous in my experience. It is the restart of the instance that takes time.

Let me know if i'm wrong there and we can definitely take a look at modifying the defaults if there is a better way now.

[knwang]

When a new deploy comes in, Heroku compiles the slug in a separate web dyno while keeping the old dyno alive, until the the new dyno is ready to route new requests to it. During this process the old dyno can still serve requests.

this is a good blog describing this process:

http://blog.carbonfive.com/2013/08/12/minimizing-downtime-when-deploying-to-heroku/

We are using paratrooper, and I have a custom rake task to deploy without turning on maintenance and it's been working fine. :)

[mattpolito]

Thanks for bringing this to my attention! Go ahead and make a pull request and we can hash it out.

As for your custom tasks... are you doing anything other than disabling maintenance mode? If so, are you using the Paratrooper 2 syntax?

[knwang]

hmm not sure about the paratrooper 2 syntax. I am using this:

  desc 'Deploy to production'
  task :production do
    deployment = Paratrooper::Deploy.new(
      "tealeaf",
      tag: 'production',
      match_tag_to: "staging",
      maintenance_mode: true)
    deployment.deploy
  end

  desc 'Deploy to production without turning on maintenance'
  task :production_hot do
    deployment = Paratrooper::Deploy.new(
      "tealeaf",
      tag: 'production',
      match_tag_to: "staging",
      maintenance_mode: false)
    deployment.deploy
  end

I'll work on PR a bit later