如何使用opsworks在部署的特定层中仅在第一个实例上运行命令？

Question

We are deploying a Laravel application on aws opsworks, everything is running great, however we need to do two other things:

1) On each deployment we want to run php artisan migrate to install the database updates.
2) We have a file (app/database/run.list) which contains a list of class names, for each line in the file we want to run php artisan db:seed --class={line from file} . eg

run.list contains

NewSystemSeed
NewUserSeed
CreateDefaultTemplatesSeed

we want to run

php artisan db:seed --class=NewSystemSeed
php artisan db:seed --class=NewUserSeed
php artisan db:seed --class=CreateDefaultTemplatesSeed

That parts not exactly difficult (although I am a bit stuck on the last one). The part that I am stuck on is, we only want to do this on the first instance in a specific layer (the php-app layer).

We obviously don't want to end up seeding the database for every instance!

Is there a way to automate this, or must we create another recipe, then after deployment manually trigger this recipe on the instance?

Answer 1

Rather than put one of your instances in a special layer, which creates a single point of failure if that instance goes down, you could choose the first instance from the list of Opsworks instances in your app layer and always do your migrations there. This allows you to keep your configuration as-is and ensures that you always run the migrations on a running instance since failed instances won't be in the list.

migrations_instance_hostname = node[:opsworks][:layers]['app-layer'][:instances].keys.sort.first

if migrations_instance_hostname == node[:opsworks][:instance][:hostname]
  # do migrations
end

Answer 2

You can use Layers as tags in OpsWorks to signal recipes.

Create a new Layer (perhaps "db-seeder"). Instead of adding a new instance in that layer, add an existing instance from your PHP layer.

Create a new custom recipe that looks like this:

if node[:opsworks][:instance][:layers].include?("db-seeder")
  config_file = 'app/database/run.list'
  bash "migrate db" do
    code %Q^
      php artisan migrate
      for clz in `cat #{config_file}` do;
        php artisan db::seed --class=${clz};
      done^
  end
end

The above recipe will only operate on an instance that is in the "db-seeder" Layer. Add this custom recipe to the "deploy" event for the PHP app layer.