Platform Events Developer Guide

Platform Events Developer Guide
Delivering Custom Notifications with Platform Events
Defining Your Custom Platform Event
Publishing Platform Events
Subscribing to Platform Events
Set Up Debug Logs
Flows
Processes
Apex Triggers
Lightning Components
Pub/Sub API
CometD
Group Your Event Streams
Filter Your Event Streams
Obtain a Platform Event’s Subscribers
Identify and Match Event Messages with the EventUuid Field
Testing Your Platform Event in Apex
Encrypting Platform Event Messages at Rest in the Event Bus
Monitor Platform Event Publishing and Delivery Usage
Considerations
Examples
Reference
PDF

Newer Version Available

This content describes an older version of this product. View Latest

Subscribe to Platform Event Messages with Flows

Launch flows or resume running instances of flows, called interviews, when platform event messages are received. Subscribed flows and interviews can receive event messages published through Apex, APIs, flows, and other processes. Flows and interviews provide an autosubscription mechanism.

Launch a Flow When a Platform Event Message Is Received

Create a platform event–triggered flow. From the Start element, choose a platform event whose event messages trigger the flow to run.

Choose a platform event for the platform event triggered flow

As you build the flow, you can use the field values from the platform event message by referencing the $Record global variable.

Resume a Flow When a Platform Event Message Is Received

To configure an autolaunched flow to subscribe to a platform event at run time, add a Pause element and set it up as follows.
  • (Optional) Specify conditions that determine whether to pause a flow interview.
  • Select the platform event that the flow interview subscribes to.
  • Identify the values that a received event message must have to resume the flow interview.
  • (Optional) Create a record variable in the flow to store the data from the event message that resumes the flow interview.

Example

This Pause element is set up to resume a flow interview when a vendor response event message is received (1). The order number in the event message must match the flow’s orderNumber variable value, and the order status must be Shipped (2). When the flow interview resumes, the vendorResponse record variable is populated with the data from the event message (3).

Screenshot of resume event configuration

Flow and Platform Event Considerations

If platform event–triggered flows, paused flow interviews, and processes are subscribed to the same platform event, we can’t guarantee which one processes each event message first.

Platform event–triggered flows and flow interviews evaluate platform event messages in the order they’re received. The order of event messages is based on the event replay ID. A flow can receive a batch of event messages at once, up to a maximum of 2,000 event messages. The order of event messages is preserved within each batch. The event messages in a batch can originate from multiple publishers.

Each platform event–triggered flow or resumed flow interview runs asynchronously in a separate transaction from the transaction that published the event message. As a result, there can be a delay between when an event message is published and when the subscribed flow or interview evaluates the event message.

Debug logs for platform event–triggered flows and resumed flow interviews appear under the Automated Process user. But each flow interview runs in the context of the user who published the event message. So, for example, if a flow interview creates or updates records, system fields like CreatedById and LastModifiedById reference the user who published the event message.

If an event fails, the flow doesn't start. Because the flow is never triggered, a flow error email isn't sent. To debug flow-related errors, look for errors generated by the platform event.