Activity Basics - .NET SDK

Develop an Activity

One of the primary things that Workflows do is orchestrate the execution of Activities. An Activity is a normal method execution that's intended to execute a single, well-defined action (either short or long-running), such as querying a database, calling a third-party API, or transcoding a media file. An Activity can interact with world outside the Temporal Platform or use a Temporal Client to interact with a Temporal Service. For the Workflow to be able to execute the Activity, we must define the Activity Definition.

You can develop an Activity Definition by using the [Activity] attribute from the Temporalio.Activities namespace on the method. To register a method as an Activity with a custom name, use an attribute parameter, for example [Activity("your-activity")]. Otherwise, the activity name is the unqualified method name (sans an "Async" suffix if the method is async).

Activities can be asynchronous or synchronous.

using Temporalio.Activities;

public class MyActivities
{
    // Activities can be async and/or static too. We just demonstrate instance methods since many
    // use them that way.
    [Activity]
    public string MyActivity(MyActivityParams input) =>
        $"{input.Greeting}, {input.Name}!";
}

There is no explicit limit to the total number of parameters that an Activity Definition may support. However, there is a limit to the total size of the data that ends up encoded into a gRPC message Payload.

A single argument is limited to a maximum size of 2 MB. And the total size of a gRPC message, which includes all the arguments, is limited to a maximum of 4 MB.

Also, keep in mind that all Payload data is recorded in the Workflow Execution Event History and large Event Histories can affect Worker performance. This is because the entire Event History could be transferred to a Worker Process with a Workflow Task.

Some SDKs require that you pass context objects, others do not. When it comes to your application data—that is, data that is serialized and encoded into a Payload—we recommend that you use a single object as an argument that wraps the application data passed to Activities. This is so that you can change what data is passed to the Activity without breaking a method signature.

Activity parameters are the method parameters of the method with the [Activity] attribute. These can be any data type Temporal can convert, including records. Technically this can be multiple parameters, but Temporal strongly encourages a single parameter containing all input fields.