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Log and store upload events in R2 with event notifications

This example provides a step-by-step guide on using event notifications to capture and store R2 upload logs in a separate bucket.

​​ Prerequisites

To continue, you will need:

​​ 1. Install Wrangler

To begin, refer to Install/Update Wrangler to install Wrangler, the Cloudflare Developer Platform CLI.

​​ 2. Create R2 buckets

You will need to create two R2 buckets:

  • example-upload-bucket: When new objects are uploaded to this bucket, your consumer Worker will write logs.
  • example-log-sink-bucket: Upload logs from example-upload-bucket will be written to this bucket.

To create the buckets, run the following Wrangler commands:

$ npx wrangler r2 bucket create example-upload-bucket
$ npx wrangler r2 bucket create example-log-sink-bucket

​​ 3. Create a queue

Event notifications capture changes to data in example-upload-bucket. You will need to create a new queue to receive notifications:

$ npx wrangler queues create example-event-notification-queue

​​ 4. Create a Worker

Before you enable event notifications for example-upload-bucket, you need to create a consumer Worker to receive the notifications.

Create a new Worker with C3 (create-cloudflare CLI). C3 is a command-line tool designed to help you set up and deploy new applications, including Workers, to Cloudflare.

$ npm create cloudflare@latest
$ yarn create cloudflare

C3 will then prompt you for some information on your Worker.

  1. Provide a name for your consumer Worker. This is also the name of the new directory where the Worker will be created.
  2. For the question “What type of application do you want to create?”, select “Hello World” Worker.
  3. For the question “Would you like to use TypeScript? (y/n)”, select y.
  4. For the question “Do you want to deploy your application?”, select n. This will create your Worker.

​​ 5. Configure your Worker

In your Worker project’s wrangler.toml file, add a queue consumer and R2 bucket binding. The queues consumer bindings will register your Worker as a consumer of your future event notifications and the R2 bucket bindings will allow your Worker to access your R2 bucket.

name = "event-notification-writer"
main = "src/index.ts"
compatibility_date = "2024-03-29"
compatibility_flags = ["nodejs_compat"]
queue = "example-event-notification-queue"
max_batch_size = 100
max_batch_timeout = 5
binding = "LOG_SINK"
bucket_name = "example-log-sink-bucket"

​​ 6. Write event notification messages to R2

Add a queue handler to src/index.ts to handle writing batches of notifications to our log sink bucket (you do not need a fetch handler):

export interface Env {
LOG_SINK: R2Bucket;
export default {
async queue(batch: MessageBatch, env: Env): Promise<void> {
const batchId = new Date().toISOString().replace(/[:.]/g, '-');
const fileName = `upload-logs-${batchId}.json`;
// Serialize the entire batch of messages to JSON
const fileContent = new TextEncoder().encode(JSON.stringify(batch.messages));
// Write the batch of messages to R2
await env.LOG_SINK.put(fileName, fileContent, {
httpMetadata: {
contentType: "application/json"

​​ 7. Deploy your Worker

To deploy your consumer Worker, run the wrangler deploy command:

$ npx wrangler deploy

​​ 8. Enable event notifications

Now that you have your consumer Worker ready to handle incoming event notification messages, you need to enable event notifications with the wrangler r2 bucket notification create command for example-upload-bucket:

$ npx wrangler r2 bucket notification create example-upload-bucket --event-type object-create --queue example-event-notification-queue

​​ 9. Test

Now you can test the full end-to-end flow by uploading an object to example-upload-bucket in the Cloudflare dashboard. After you have uploaded an object, logs will appear in example-log-sink-bucket in a few seconds.