Reactions are configured to react to a specific event and trigger an action whenever that event is processed by the event reactor. An example could be sending a confirmation email to a customer when an order has been successfully placed.

It is not possible for a Reaction to trigger on an event that has happened in the past. Reactions are always configured to listen to events from the moment when the Reaction is configured.

Actions

Each reaction is configured with a specific Action that defines what will happen when the reaction is triggered. When a Reaction is triggered it will execute its configured Action.

Currently Serialized offer two different pre-defined action types that you can use to integrate with external systems. The specific Slack action and the more generic HTTP action

HTTP Action

The action type (HTTP_POST) requires the field targetUri to be populated with the address that should receive the POST request. Optionally the field httpHeaders can be set, i.e. to handle Basic Authentication etc.

Receiving reaction requests

The reaction requests are HTTP POST requests with a JSON body. The JSON has the following format:

{  
   "metadata":{  
      "aggregateId":"<some-aggregate-id>",
      "timestamp": <epoc-millis>,
      "sequenceNumber": <n>
   },
   "event":{  
      "eventId":"<some-event-id>",
      "eventType":"<event-type>",
      "data":{  
         "key":"value",
         "key":"value",
         ...
      }
   }
}

Securing the external endpoint

As the end-point specified in the targetUri must be exposed to the public internet it should be protected. Currently it’s possible to utilize Basic Authentication and include the appropriate HTTP header in the Reaction definition.

{
  "reactionName": "notify-on-order-shipped",
  "feedName": "order",
  "reactOnEventType": "OrderShippedEvent",
  "action": {
    "actionType": "HTTP_POST",
    "targetUri": "https://your-service",
    "httpHeaders": {
      "Authorization": "Basic c2VasXlZdyW2dGsONfM5fD4adleRDgVbDNgRkgFgZUpgoxgNHdsg15QktFcm1ndjI="
    }    
  }
}

Slack Action

The action type (SLACK_POST) requires the field targetUri to be populated with a valid Slack webhook URI. The message text is specified in the field body. Simple templating is supported and event data can be accessed using dot (.) notation.

Example of a Reaction posting a notification to Slack:

{
  "reactionName": "on-order-placed-slack-notifier",
  "feedName": "order",
  "reactOnEventType": "OrderPlacedEvent",
  "action": {
    "actionType": "SLACK_POST",
    "targetUri": "https://hooks.slack.com/services/T0000/B0000/XXXX",
    "body": "A new order with number ${event.data.orderNumber} was placed by ${event.data.customer.email}!"
  }
}

Given this event:

{
  "eventId": "ca37d05c-a852-4de5-961f-16fb35e8cd7b",
  "eventType": "OrderPlacedEvent",
  "data": {  
    "orderNumber": "12312345",
    "customer": {
      "email": "customer@example.com"
    }
  }
}

the message to Slack will look like this:

A new order with number 12312345 was placed by customer@example.com!

Automatic retries

Serialized Reactions have a built-in retry mechanism and will be retried several times over the course of a day. A 2xx response is required for success, whereas a 4xx or 5xx response will be treated as an error and retried.