Core Resource Model

Important: These docs are for the outdated Jets 5 versions and below. For the latest Jets docs: docs.rubyonjets.com

At the core of Jets is the resource model. Understanding the core resource model and method will allow you to create any resource supported by CloudFormation with Jets.

All Paths Lead to resource

An important learning point is that all resources associated with each Lambda function in Jets are ultimately created by the resource method. The resource method is the key.

For example, the rate method creates a CloudWatch Event Rule resource. This Event Rule resource is associated with the dig Lambda function. Here’s an example:

class HardJob < ApplicationJob
  rate "10 hours" # every 10 hours
  def dig
    puts "done digging"
  end
end

What’s happens is that Jets takes the rate method, performs some wrapper logic, and calls the core resource method. In other words, the code could also be written like so:

class HardJob < ApplicationJob
  resource(
    HardJobDigEventsRule: {
      Type: "AWS::Events::Rule",
      Properties: {
        ScheduleExpression: "rate(10 hours)",
        State: "ENABLED",
        Targets: [{
          Arn: "!GetAtt HardJobDigLambdaFunction.Arn",
          Id: "HardJobDigRuleTarget"
        }]
      }
    }
  )
  def dig
    puts "done digging"
  end
end

The resource method creates the AWS::Events::Rule as a CloudFormation resource.

With this design, you can create any resource with Jets and associate them with your Lambda functions. Once you understand how the resource method works, you can define any resource that you required. Methods like rate, cron, rule_event simply run some setup logic and call the resource method.

Note: Users who have used Jets for a while, IE, jets v3 and below, may notice that the CloudFormation keys are CamelCase not underscore. Both underscore and CamelCase works. Jets runs a custom Camelizer to properly transform the keys regardless of the format. You can use either format. Have found that once we get near CloudFormation land, it’s easier to think on CloudFormation terms. Feel that resource at the crossing of that mental boundary. More thoughts: CloudFomation CamelCase vs Ruby Underscore Thoughts.

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