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.

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;
	}
}

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.

{
	"$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"
			]
		}
	]
}

"$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" ]