An invocation is a request to execute a handler that is part of a Restate service. There are three ways to invoke a handler: over HTTP, using typed clients, or through Kafka topics.

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HTTP invocations

To call a function over HTTP, send a request to the Restate Server, specifying the service and the function you want to invoke. For example, to call the processPayment function of the PaymentService: 
curl -X POST localhost:8080/PaymentService/processPayment \
--json '{"amount": 100, "currency": "USD"}'
The Restate Server ingress endpoint is here hosted at localhost:8080. To call Virtual Objects or Workflows, you need to specify the object key or workflow ID in the URL. For example, to call updateBalance of the UserAccount object with key user123: 
curl -X POST localhost:8080/UserAccount/user123/updateBalance \
--json '{"amount": 50}'
Check out the HTTP invocation docs to learn more.

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Typed client invocations

Use typed clients from external applications to invoke Restate handlers: 
//import * as clients from "@restatedev/restate-sdk-clients";
const restateClient = clients.connect({ url: "http://localhost:8080" });

// To call a service:
const greet = await restateClient
  .serviceClient(greeterService)
  .greet({ greeting: "Hi" });
For service-to-service calls within handlers, see Service Communication.

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Kafka invocations

You can connect your Restate handlers to Kafka topics, to let Restate invoke them for each message. Consult the Kafka Quickstart to get started.

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Idempotency

Add an idempotency key to your request header to let Restate deduplicate retries: 
curl -X POST localhost:8080/PaymentService/processPayment \
-H 'idempotency-key: payment-123' \
--json '{"amount": 100, "currency": "USD"}'
On retry, Restate returns the first invocation’s result or lets you attach to it if still running.

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Inspecting invocations

Use the Restate UI to monitor and troubleshoot invocations:
Durable Execution

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Attaching to invocations

Attach to ongoing invocations to retrieve their results: 
const handle = ctx
  .serviceSendClient(myService)
  .myHandler("Hi", sendOpts({ idempotencyKey: "my-key" }));
const invocationId = await handle.invocationId;

// Later...
const response = ctx.attach(invocationId);
Or over HTTP: 
curl localhost:8080/restate/invocation/inv_1234567890abcdef/attach
This is useful when another process needs the result of an ongoing operation or wants to check whether it has completed.

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Cancelling invocations

Cancel running invocations when they’re no longer needed: 
restate invocations cancel inv_1234567890abcdef
Or programmatically: 
const handle = ctx.serviceSendClient(myService).myHandler("Hi");
const invocationId = await handle.invocationId;

// Cancel the invocation
ctx.cancel(invocationId);
To roll back the actions the handler already completed before cancellation, check out at the sagas guide.