Idempotency

Idempotency is a crucial feature for building reliable integrations with Novu's API. It allows you to safely retry requests without worrying about duplicate operations, which is especially important for critical actions like triggering workflows.

An idempotent request is one that can be made multiple times with the same effect as making it once. This is achieved by including a unique idempotency key with your request.

How It Works

When you send a request with an idempotency key:

1. Novu checks if a request with the same key has been processed before
2. If it's a new key, the request is processed normally and the response is cached
3. If the key was seen before, Novu returns the cached response without reprocessing the request

This mechanism protects against network issues, timeouts, and other scenarios where a request might be retried.

Trigger events and billing

On POST /v1/events/trigger, idempotency keys are enforced at the API layer before the request is queued. If you send 100 requests with the same Idempotency-Key, only the first is processed. Once that request completes, subsequent requests receive the cached response and count as one workflow run toward billing. While the first request is still in progress, duplicates receive a 409 Conflict response and are not queued.

This differs from the optional transactionId request field, which is checked for uniqueness during trigger processing rather than at the API boundary. transactionId is useful for tracing and cancellation, but it does not provide the same deduplication or billing protection as an idempotency key. For safe retries, always prefer Idempotency-Key. See the Trigger event API reference and Trigger concepts page for details.

Using Idempotency Keys

To make an idempotent trigger request, pass a unique idempotency key with your request:

const novu = new Novu({ secretKey: "<NOVU_SECRET_KEY>" });

await novu.trigger( { workflowId: "workflow-id", to: "unique_subscriber_identifier", payload: { postId: "123", }, }, // Idempotency key "unique-request-id-12345" );

  </Tab>
  <Tab title="Python">
```python
import os
import novu_py
from novu_py import Novu

with Novu(secret_key=os.getenv("NOVU_SECRET_KEY", "")) as novu:
    novu.trigger(
        trigger_event_request_dto=novu_py.TriggerEventRequestDto(
            workflow_id="workflow-id",
            to="unique_subscriber_identifier",
            payload={
                "postId": "123",
            },
        ),
        idempotency_key="unique-request-id-12345",
    )

novugo "github.com/novuhq/novu-go"
"github.com/novuhq/novu-go/models/components"

)

s := novugo.New(novugo.WithSecurity(os.Getenv("NOVU_SECRET_KEY")))

idempotencyKey := "unique-request-id-12345"

res, err := s.Trigger(context.Background(), components.TriggerEventRequestDto{ WorkflowID: "workflow-id", To: components.CreateToStr("unique_subscriber_identifier"), Payload: map[string]any{ "postId": "123", }, }, &idempotencyKey)

  </Tab>
  <Tab title="PHP">
```php
use novu;
use novu\Models\Components;

$sdk = novu\Novu::builder()->setSecurity('<NOVU_SECRET_KEY>')->build();

$sdk->trigger(
    triggerEventRequestDto: new Components\TriggerEventRequestDto(
        workflowId: 'workflow-id',
        to: 'unique_subscriber_identifier',
        payload: ['postId' => '123'],
    ),
    idempotencyKey: 'unique-request-id-12345',
);

var sdk = new NovuSDK(secretKey: "<NOVU_SECRET_KEY>");

await sdk.TriggerAsync( triggerEventRequestDto: new TriggerEventRequestDto() { WorkflowId = "workflow-id", To = To.CreateStr("unique_subscriber_identifier"), Payload = new Dictionary<string, object>() { { "postId", "123" }, }, }, idempotencyKey: "unique-request-id-12345" );

  </Tab>
  <Tab title="Java">
```java
import co.novu.Novu;
import co.novu.models.components.*;
import java.util.Map;

Novu novu = Novu.builder().secretKey("<NOVU_SECRET_KEY>").build();

novu.trigger()
    .idempotencyKey("unique-request-id-12345")
    .body(TriggerEventRequestDto.builder()
        .workflowId("workflow-id")
        .to(To2.of("unique_subscriber_identifier"))
        .payload(Map.of("postId", "123"))
        .build())
    .call();

Key Requirements

• Maximum length: 255 characters
• Uniqueness: Keys should be unique per organization
• Format: Any string value (UUIDs are recommended)

Supported Methods

Idempotency is supported for the following HTTP methods:

Authentication Requirements

Idempotency is only available when authenticating with an API Key. Include the Authorization: ApiKey <NOVU_SECRET_KEY> header, as shown in the cURL tab above.

Requests using other authentication methods will be processed normally without idempotency support.

Cache Duration

After the cache expires, the same idempotency key can be reused.

HTTP Response Headers

When making idempotent requests, Novu includes helpful headers in the response:

Idempotency-Key

Confirms the idempotency key that was used for the request:

Idempotency-Key: unique-request-id-12345

Idempotency-Replay

Indicates that the response was served from the cache rather than processing a new request:

Idempotency-Replay: true

This header is only present when returning a cached response.

Error Handling

Request In Progress (409 Conflict)

If you send a request with an idempotency key while a previous request with the same key is still being processed:

{
  "statusCode": 409,
  "message": "Request with key \"unique-request-id-12345\" is currently being processed. Please retry after 1 second"
}

The response includes a Retry-After header indicating when to retry:

Retry-After: 1

Key Reused with Different Body (422 Unprocessable Entity)

If you send a request with an idempotency key that was previously used with a different request body:

{
  "statusCode": 422,
  "message": "Request with key \"unique-request-id-12345\" is being reused for a different body"
}

Key Too Long (400 Bad Request)

If the idempotency key exceeds 255 characters:

{
  "statusCode": 400,
  "message": "idempotencyKey \"...\" has exceeded the maximum allowed length of 255 characters"
}

Best Practices

1. Generate unique keys: Use UUIDs or combine entity IDs with timestamps to ensure uniqueness
2. Store keys: Keep track of idempotency keys you've used in case you need to retry requests
3. Handle 409 responses: Implement retry logic with exponential backoff when you receive a conflict response
4. Don't reuse keys for different operations: Each unique operation should have its own idempotency key
5. Include meaningful context: Consider including the operation type and relevant IDs in your key for easier debugging

Example: Safe Retry Logic

Here's an example of implementing safe retry logic with idempotency:

import { Novu } from '@novu/api';
import { v4 as uuidv4 } from 'uuid';

const novu = new Novu({
  secretKey: "<NOVU_SECRET_KEY>"
});

async function triggerNotificationWithRetry(workflowId, subscriberId, payload, maxRetries = 3) {

  const uniqueId = uuidv4();
  const idempotencyKey = `trigger-${workflowId}-${subscriberId}-${uniqueId}`;
  
  for (let attempt = 1; attempt <= maxRetries; attempt++) {
    try {
      const response = await novu.trigger({
        workflowId: workflowId,
        to: { subscriberId: subscriberId },
        payload,
      }, idempotencyKey);
        
      return response;
    } catch (error) {
      if (error.statusCode === 409 && attempt < maxRetries) {
        // Request in progress, wait and retry
        const retryAfter = error.headers?.['retry-after'] || 1;
        await new Promise(resolve => setTimeout(resolve, retryAfter * 1000));
        continue;
      }
      throw error;
    }
  }
}