Services or capabilities described in Amazon Web Services documentation might vary by Region. To see the differences applicable to the China Regions, see Getting Started with Amazon Web Services in China (PDF).

Event bus target: bus to bus

To forward events to another event bus, set TargetArn to that bus's ARN. The destination can be another Custom Event Bus or a Custom Event Bus - Classic, in the same Region or a different one. The destination bus must be in the same account as the subscriber. No parameter block is needed. A Custom Event Bus - Classic rule can likewise name a Custom Event Bus as its target, so events can move in either direction during a migration.

Parameters

This target has no parameters; the payload is the whole request.

Delivery role

The role needs events:PutEvents on the destination bus for events that carry a PutEvents envelope, and events:PutRawEvents for events published with PutRawEvents. EventBridge chooses the action per event and you cannot override it, so grant both when the source bus carries both kinds. EventBridge rejects a subscriber whose target is in another account, including a bus that is shared with you through Amazon RAM. To deliver events to another account, share the source bus with that account so that it can create its own subscriber on the bus; see Sharing a Custom Event Bus with other accounts.

Batching and payload

Events arrive on the destination bus as new events: they get a new event identifier and ingestion time, and the destination bus's subscribers filter them as usual. Publishing to the destination counts against that bus's throughput quota.

Loop detection

A chain of buses, rules, subscribers, and functions can send an event back to a bus it already passed through, and multiply it on each pass. EventBridge detects such loops through a Custom Event Bus on a best-effort basis: if an event, or an event derived from it, already passed through the target Custom Event Bus, EventBridge does not deliver it again, and if the subscriber has a dead-letter queue, the record carries the error code LOOP_DETECTED. Do not design an application that depends on an event passing through the same bus more than once, and do not rely on EventBridge to stop a loop for you. Rules on a Custom Event Bus - Classic keep their existing behavior; see Preventing infinite loops.