Use the Alarms API

This example implements an alarm() handler that allows batching of requests to a single Durable Object.

When a request is received and no alarm is set, it sets an alarm for 10 seconds in the future. The alarm() handler processes all requests received within that 10-second window.

If no new requests are received, no further alarms will be set until the next request arrives.

JavaScript

JavaScript

import { DurableObject } from "cloudflare:workers";

// Worker
export default {
  async fetch(request, env) {
    return await env.BATCHER.getByName("foo").fetch(request);
  },
};

// Durable Object
export class Batcher extends DurableObject {
  constructor(ctx, env) {
    super(ctx, env);
    this.storage = ctx.storage;
    this.ctx.blockConcurrencyWhile(async () => {
      let vals = await this.storage.list({ reverse: true, limit: 1 });
      this.count = vals.size == 0 ? 0 : parseInt(vals.keys().next().value);
    });
  }

  async fetch(request) {
    this.count++;

    // If there is no alarm currently set, set one for 10 seconds from now
    // Any further POSTs in the next 10 seconds will be part of this batch.
    let currentAlarm = await this.storage.getAlarm();
    if (currentAlarm == null) {
      this.storage.setAlarm(Date.now() + 1000 * 10);
    }

    // Add the request to the batch.
    await this.storage.put(this.count, await request.text());
    return new Response(JSON.stringify({ queued: this.count }), {
      headers: {
        "content-type": "application/json;charset=UTF-8",
      },
    });
  }

  async alarm() {
    let vals = await this.storage.list();
    await fetch("http://example.com/some-upstream-service", {
      method: "POST",
      body: Array.from(vals.values()),
    });
    await this.storage.deleteAll();
    this.count = 0;
  }
}

Python

Python

from workers import DurableObject, Response, WorkerEntrypoint, fetch
import time

# Worker
class Default(WorkerEntrypoint):
  async def fetch(self, request):
    stub = self.env.BATCHER.getByName("foo")
    return await stub.fetch(request)

# Durable Object
class Batcher(DurableObject):
  def __init__(self, ctx, env):
    super().__init__(ctx, env)
    self.storage = ctx.storage

    @self.ctx.blockConcurrencyWhile
    async def initialize():
      vals = await self.storage.list(reverse=True, limit=1)
      self.count = 0
      if len(vals) > 0:
          self.count = int(vals.keys().next().value)

  async def fetch(self, request):
    self.count += 1

    # If there is no alarm currently set, set one for 10 seconds from now
    # Any further POSTs in the next 10 seconds will be part of this batch.
    current_alarm = await self.storage.getAlarm()
    if current_alarm is None:
      self.storage.setAlarm(int(time.time() * 1000) + 1000 * 10)

    # Add the request to the batch.
    await self.storage.put(self.count, await request.text())
    return Response.json(
      {"queued": self.count}
    )

  async def alarm(self):
    vals = await self.storage.list()
    await fetch(
      "http://example.com/some-upstream-service",
      method="POST",
      body=list(vals.values())
    )
    await self.storage.deleteAll()
    self.count = 0

The alarm() handler will be called once every 10 seconds. If an unexpected error terminates the Durable Object, the alarm() handler will be re-instantiated on another machine. Following a short delay, the alarm() handler will run from the beginning on the other machine.

Finally, configure your Wrangler file to include a Durable Object binding and migration based on the namespace and class name chosen previously.

wrangler.jsonc

{
  "$schema": "./node_modules/wrangler/config-schema.json",
  "name": "durable-object-alarm",
  "main": "src/index.ts",
  "durable_objects": {
    "bindings": [
      {
        "name": "BATCHER",
        "class_name": "Batcher"
      }
    ]
  },
  "migrations": [
    {
      "tag": "v1",
      "new_sqlite_classes": [
        "Batcher"
      ]
    }
  ]
}

wrangler.toml

name = "durable-object-alarm"
main = "src/index.ts"

[[durable_objects.bindings]]
name = "BATCHER"
class_name = "Batcher"

[[migrations]]
tag = "v1"
new_sqlite_classes = ["Batcher"]