Event routing rules
The rules you create in EventBridge are the logic behind the filtering and routing of events that you associate with an event bus. These rules are effectively part of your application logic, and are designed, documented, deployed, and tested as such. A rule comprises three parts: the event filter pattern, event data transformation, and the target(s).
To filter an event in and send it to a target, you configure an event pattern as your filter condition. The sample pattern in Example 3-2 will match events like the one in Example 3-1 based on the domain, service, type, and payment_type attribute values.
Example 3-2. An example event filter pattern
{
“detail”
:
{
“metadata”
:
{
“domain”
:
[
“ecommerce”
],
“service”
:
[
“service-payments”
],
“type”
:
[
“payment_received”
]
},
“data”
:
{
“payment_type”
:
[
“creditcard”
]
}
}
}
As part of each rule, you can perform simple data transformations. At the time of writing, for each rule you can add up to five targets to send matching events to.
An important fact to keep in mind is that EventBridge guarantees at least once delivery of events to targets. This means a target may receive an event more than once (i.e., it may receive duplicate events). You will learn how to handle this situation later in the chapter.
Event archiving and replay
In EventBridge, you can store events in one or more archives. The events you archive depend on the event filter pattern. For example, you could create an archive to store all the events that match the pattern shown in Example 3-2.
You can create multiple archives to cater to your needs. Then, based on your business requirements, you can identify the events within your bounded context that need archiving and send them to the appropriate archives using different filter conditions. Unless there is a specific requirement to archive all the events, keep your archives as lean as possible as a best practice. Figure 3-40 shows a comparison of the different approaches for a better understanding.
To replay events from an archive, you specify the archive name and the time window. EventBridge reads the events from the archive and puts them onto the same event bus that originally emitted them. To differentiate a replayed event from the original event, EventBridge adds a replay-name attribute.
