Distributed Counter

Author: Firebase (https://firebase.google.com)

Description: Records event counters at scale to accommodate high-velocity writes to Cloud Firestore.

Details: Use this extension to add a highly scalable counter service to your app. This is ideal for applications that count viral actions or any very high-velocity action such as views, likes, or shares.

Since Cloud Firestore has a limit of one sustained write per second, per document, this extension instead shards your writes across documents in a _counter_shards_ subcollection. Each client only increments their own unique shard while the background workers (provided by this extension) monitor and aggregate these shards into a main document.

Here are some features of this extension:

Scales from 0 updates per second to a maximum of 10,000 per second.
Supports an arbitrary number of counters in your app.
Works offline and provides latency compensation for the main counter.

Note that this extension requires client-side logic to work. We provide a TypeScript client sample implementation and its compiled minified JavaScript. You can use this extension on other platforms if you'd like to develop your own client code based on the provided client sample.

We also provide a Node.js admin sample implementation

Additional setup

Before installing this extension, make sure that you've set up a Cloud Firestore database in your Firebase project.

After installing this extension, you'll need to:

Update your database security rules.
Use the provided client sample, the provided Node.js admin sample or your own client code to specify your document path and increment values.

Detailed information for these post-installation tasks are provided after you install this extension.

Billing

To install an extension, your project must be on the Blaze (pay as you go) plan

This extension uses other Firebase and Google Cloud Platform services, which have associated charges if you exceed the service’s no-cost tier:
Cloud Firestore
Cloud Functions (Node.js 10+ runtime. See FAQs)

Configuration Parameters:

Document path for internal state: What is the path to the document where the extension can keep its internal state?
Frequency for controllerCore function to be run: In minutes, how often should the function to aggregate shards be run?

Cloud Functions:

controllerCore: This scheduled function either aggregates shards itself, or it schedules and monitors workers to aggregate shards.
onWrite: Listens for changes on counter shards that may need aggregating. This function is limited to max 1 instance.
worker: Monitors a range of shards and aggregates them, as needed. There may be 0 or more worker functions running at any point in time. The controllerCore function is responsible for scheduling and monitoring these workers.

Access Required:

This extension will operate with the following project IAM roles:

datastore.user (Reason: Allows the extension to aggregate Cloud Firestore counter shards.)
cloudscheduler.admin (Reason: Allows the extension to create a new Cloud Scheduler function.)