Nexus Standalone Activity
The two names are close and describe opposite ends of the call. A Standalone Nexus Operation is about the caller: a Client starts an Operation directly, with no caller Workflow around it. A Nexus Standalone Activity is about the handler: an Operation is backed by a single Activity, with no Workflow behind it. They are independent choices, and either can be used without the other.
An Activity-backed Nexus Operation runs a Standalone Activity and completes when that Activity returns. Use it when the work behind an Operation is one durable step rather than a process: calling an external API, running a computation, writing to another system.
Two things combine to make this happen. The Activity supplies durability — retries on the policy you set, timeouts you control, and a record of every attempt. The Operation supplies a typed contract and a Namespace boundary, so another team can call it without sharing your code, your deployment, or write access to your Namespace.
Because the Activity carries the durability, no Workflow is needed behind the Operation. A Workflow wrapping a single Activity costs two Billable Actions in Temporal Cloud — one to start the Workflow, one to start the Activity — where a Standalone Activity costs one. Retries and heartbeats are billed the same way in either shape.
Required options
Starting an Activity this way needs values a Workflow-called Activity does not, because there is no parent Workflow to supply them:
- An Activity Id, unique within the Namespace. Deriving it from the Nexus request Id makes the start idempotent, so a retried request targets the same Activity Execution instead of sending a second notification or charge.
- A timeout. At least one of start-to-close or schedule-to-close.
The Task Queue is optional and defaults to the one the Operation is running on. Set it explicitly to run the Activity on its own Worker fleet.
Cancellation
An Activity is not interrupted by a cancellation request the way a Workflow is. The Worker only learns about it on the next Heartbeat, so an Activity that never Heartbeats runs until it completes or times out. Nothing here is Nexus-specific — see Activity Cancellation.
Back an Operation with a Workflow instead when the work has more than one step, needs to wait for something, needs to receive messages, or needs durable intermediate state.