SNS Events

Jets supports SNS Events as a Lambda trigger. So you can send a message to an SNS topic and it triggers a Lambda function to run. The Lambda function has access to the message data via event.

There are a few ways to connect an SNS topic to a Lambda function with Jets.

  1. Existing SNS Topic
  2. Generated Function SNS Topic
  3. Generated Shared SNS Topic

We’ll cover each of them:

Existing SNS Topic

Here is an example connecting an existing SNS topic to a Lambda function in a Event

Generate code.

jets generate:event messenger --trigger sns --method deliver

It looks something like this.

app/events/messenger_event.rb

class MessengerEvent < ApplicationEvent
  sns_event "hello-topic"
  def deliver
    puts "event #{JSON.dump(event)}"
    puts "sns_events #{JSON.dump(sns_events)}"
  end
end

Ultimately, the sns_event declaration generates a SNS::Subscription. The properties of the subscription can be set with an additional Hash argument:

  sns_event("hello-topic", filter_policy: {store: "example_corp"})

There’s more information on the filter_policy here on SNS Message Filtering.

Generated Function SNS Topic

Jets can create and manage an SNS Topic for a specific function. This is done with a special :generate_topic argument.

class CoolEvent < ApplicationEvent
  sns_event :generate_topic
  def lift
    puts "lift event #{JSON.dump(event)}"
  end
end

A special :topic_properties key will set the SNS::Topic properties. Other keys set the SNS::Subscription properties. Example:

  sns_event(:generate_topic,
    batch_size: 10,
    topic_properties: {display_name: "My awesome topic"}
  )

Here’s an example screenshot of a generated SNS topic:

Note, SNS Topics managed by Jets are deleted when you delete the Jets application.

Generated Shared SNS Topic

Jets can also support creating a shared SNS Topic via a Shared Resource. Here’s how you create the SNS Topic as a shared resource:

shared/resources/topic.rb

class Topic < Jets::Stack
  sns_topic(:engineering)
end

You can reference the Shared Topic like so:

app/events/cool_event.rb

class CoolEvent < ApplicationEvent
  depends_on :topic # so we can reference topic shared resources
  sns_event ref(:engineering) # reference sns topic in shared resource
  def fix
    puts "fix #{JSON.dump(event)}"
  end
end

Underneath the hood, Jets provisions resources via CloudFormation. The use of depends_on ensures that Jets will pass the shared resource Topic stack outputs to the CoolEvent stack as input parameters. This allows CoolEvent to reference resources from the separate child Topic stack.

For those learning CloudFormation, these resources might help:

Publish Test Message

Here’s an example of publishing a test message to an SNS topic via the aws sns publish CLI:

aws sns publish --topic-arn arn:aws:sns:us-west-2:112233445566:my-topic --message '{"default": "test message"}'

You can send a message via the SNS Console, sdk, etc also.

Tailing Logs

It helps to tail the logs and watch the event as it comes through.

jets logs -f -n messenger_event-deliver

Event Payloads

{
    "Records": [
        {
            "EventSource": "aws:sns",
            "EventVersion": "1.0",
            "EventSubscriptionArn": "arn:aws:sns:us-west-2:112233445566:demo-dev-Topic-JSTMFREHSV9U-Engineering-1PS3HM70TS67H:ba5887af-fe4c-44c9-bbd7-f7f0e6d652de",
            "Sns": {
                "Type": "Notification",
                "MessageId": "e3d54a5f-fee2-51cc-abc7-1eb99d074475",
                "TopicArn": "arn:aws:sns:us-west-2:112233445566:demo-dev-Topic-JSTMFREHSV9U-Engineering-1PS3HM70TS67H",
                "Subject": null,
                "Message": "{\"default\": \"test message\"}",
                "Timestamp": "2019-02-19T20:05:57.063Z",
                "SignatureVersion": "1",
                "Signature": "XDv0YTmNgyfqTLiWDev6ZRMkl9PoWnlAYIM5jW9PmPRrYG+TdfDAxcxmD7gYsEk3Eol/EqtBlFHTjWVcH7F6JQDu6hNO1P4f/k0VLGX94AdMP51riGDAC/S4yuHPT1Muq1WLFuT/Ttol1cTW2UH5kVMG7eIOfNTt4Qe3Kf4q2pRNTh5Z2EGULgjkea//OsRIfz3vfLlNUTyn1JKp2Q427CpoSZ/4YSk/wdL7IEVzWbKssgkiITIzLxS/KUr30OF+WLCnvHbBLVXo8nyscRTHRho6cgC4QtjUL6XOeXh5EPg4NB0i5nzgBe+2xIgXne5yMUHIWwW6fQ8Ouq+UliO4ZA==",
                "SigningCertUrl": "https://sns.us-west-2.amazonaws.com/SimpleNotificationService-ac565b8b1a6c5d002d285f9598aa1d9b.pem",
                "UnsubscribeUrl": "https://sns.us-west-2.amazonaws.com/?Action=Unsubscribe&SubscriptionArn=arn:aws:sns:us-west-2:112233445566:demo-dev-Topic-JSTMFREHSV9U-Engineering-1PS3HM70TS67H:ba5887af-fe4c-44c9-bbd7-f7f0e6d652de",
                "MessageAttributes": {}
            }
        }
    ]
}

sns_events

The sns_events helper method unravels the data and provides the SNS message payloads.

[{
  "default": "test message"
}]

In this section: