PURISTA

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Default Event Bridge ​

The core package comes with DefaultEventBridge, which will work on local without any further installation. The DefaultEventBridge acts as event bridge and simple message broker.

It should work out of the box for single instances. You can also use it, for simple horizontal scaling, but the messages and states are not shared or load balanced between instances.

This means a subscription is always running on the same instance. Also, any command invocation is done within the same instance. Sharing of states and data must be done over third party software, like usage of redis or other databases.

Because of this, the DefaultEventBridge will only work for scenarios, where you deploy your services as single instance monolith (edge) and you don't have the requirement to share messages and states across instances.

A simplified schema of how the DefaultEventBridge works:

single instance

Pros

  • no extra message broker needed
  • full subscription support
  • ideal for local development and debug purpose

Cons

  • does not scale
  • no persistance of messages
  • no retry mechanism for messages

Configuration ​

The DefaultEventBridge can be configured to emit every message, which has set the eventName property as javascript event. This must be enabled in the configuration by setting the emitMessagesAsEventBridgeEvents property to true. Than, you can subscribe to specific events in regular JavaScript fashion. The event names will be prefixed with custom- to avoid name collisions.

Usage example ​

typescript
import { DefaultEventBridge } from '@purista/core'

const eventBridge = new DefaultEventBridge({ emitMessagesAsEventBridgeEvents: true })
await eventBridge.start()

eventBridge.on('custom-example-event', (msg)=> {
  console.log(JSON.stringify(msg, null, 2))
})

// ... register and start your services