Bindings

When you deploy User Workers through Workers for Platforms, you can attach bindings to give them access to resources like KV namespaces, D1 databases, R2 buckets, and more. This enables your end customers to build more powerful applications without you having to build the infrastructure components yourself.

With bindings, each of your users can have their own:

• KV namespace that they can use to store and retrieve data
• R2 bucket that they can use to store files and assets
• Analytics Engine dataset that they can use to collect observability data
• Durable Objects class that they can use for stateful coordination

Resource isolation

Each User Worker can only access the bindings that are explicitly attached to it. For complete isolation, you can create and attach a unique resource (like a D1 database or KV namespace) to every User Worker.

Resource Isolation Model

Adding a KV Namespace to a User Worker

This example walks through how to create a KV namespace and attach it to a User Worker. The same process can be used to attach to other bindings.

1. Create a KV namespace

Create a KV namespace using the Cloudflare API.

2. Attach the KV namespace to the User Worker

Use the Upload User Worker API to attach the KV namespace binding to the Worker. You can do this when you're first uploading the Worker script or when updating an existing Worker.

Note

When using the API to upload scripts, bindings must be specified in the metadata object of your multipart upload request. You cannot upload the wrangler.toml file as a module to configure the bindings. For more details about multipart uploads, see Multipart upload metadata.

Example API request

curl -X PUT \
  "https://api.cloudflare.com/client/v4/accounts/<account-id>/workers/dispatch/namespaces/<your-namespace>/scripts/<script-name>" \
  -H "Content-Type: multipart/form-data" \
  -H "Authorization: Bearer <api-token>" \
  -F 'metadata={
    "main_module": "worker.js",
    "bindings": [
      {
        "type": "kv_namespace",
        "name": "USER_KV",
        "namespace_id": "<your-namespace-id>"
      }
    ]
  }' \
  -F 'worker.js=@/path/to/worker.js'

Now, the User Worker has can access the USER_KV binding through the env argument using env.USER_DATA.get(), env.USER_DATA.put(), and other KV methods.

Note: If you plan to add new bindings to the Worker, use the keep_bindings parameter to ensure existing bindings are preserved while adding new ones.

curl -X PUT \
  "https://api.cloudflare.com/client/v4/accounts/<account-id>/workers/dispatch/namespaces/<your-namespace>/scripts/<script-name>" \
  -H "Content-Type: multipart/form-data" \
  -H "Authorization: Bearer <api-token>" \
  -F 'metadata={
    "bindings": [
      {
        "type": "r2_bucket",
        "name": "STORAGE",
        "bucket_name": "<your-bucket-name>"
      }
    ],
    "keep_bindings": ["kv_namespace"]
  }'