Associated Function Resource Extensions

You can define your own custom associated resource methods. This helps for shorter and cleaner code. Remember that methods like cron and rate are just convenience methods that ultimately call the resource method. You can extend Jets with custom convenience methods.

Example Extension

To define a custom extension, you create a module in the app/extensions folder. Here’s an example:

app/extensions/iot_extension.rb

module IotExtension
  def thermostat_rule(logical_id, props = {})
    defaults = {
      topic_rule_payload: {
        sql: "SELECT * FROM 'TemperatureTopic' WHERE temperature > 60",
        actions: [
          lambda: {function_arn: "!Ref {namespace}LambdaFunction"}
        ],
        rule_disabled: true
      }
    }
    props = defaults.deep_merge(props)
    resource(logical_id, "AWS::IoT::TopicRule", props)
  end
end

Note: Astute users may noticed that underscore for the keys is used. This allows the user to use underscore when using thermostat_rule, once props reaches the resource call, the resource call will internally camelize the keys. If the helper is meant to be user-facing, then underscore is probably what Ruby-ist would use. If you’re writing internal Jets code, CamelCalse is used since we’re working closely with CloudFormation properties.

After the module is defined, you can use the newly created convenience method like so:

app/events/temperature_event.rb

class TemperatureEvent < ApplicationEvent
  thermostat_rule(:room)
  def record
    # custom business logic
    puts "record event #{JSON.dump(event)}"
  end
end

The code above creates an AWS::IoT::TopicRule and runs the record Lambda function for incoming IoT thermostat data. You can add your own custom business logic to handle the received data accordingly.

Three Resource Forms

You might have noticed that the thermostat_rule extension used a different form of the resource method. There are 3 different forms of the resource method. Here are examples of each:

Resource Long Form

def thermostat_rule(logical_id, props={})
  # ...
  resource(
    logical_id : {
      Type: "AWS::IoT::TopicRule",
      Properties: props
    }
  )
end

Resource Medium Form

def thermostat_rule(logical_id, props={})
  # ...
  resource(logical_id,
    Type: "AWS::IoT::TopicRule",
    Properties: props
  )
end

Resource Short Form

def thermostat_rule(logical_id, props={})
  # ...
  resource(logical_id, "AWS::IoT::TopicRule", props)
end

Which one to use?

You can use any of the resource forms depending on how much customization and control is needed. It is probably best to try the simplest form first and then go up your way to the long form when needed.

In this section: