For the past five months I’ve been leading the efforts to rebuild Zed’s cloud infrastructure.

Our current backend—known as Collab—has been chugging along since basically the beginning of the company. We use Collab every day to work together on Zed in Zed. However, as Zed continues to grow and attracts more users, we knew that we needed a full reboot of our backend infrastructure to set us up for success for our future endeavors.

Enter Zed Cloud.

Like Zed itself, Zed Cloud is built in Rust1.

This time around there is a slight twist: all of this is running on Cloudflare Workers, with our Rust code being compiled down to WebAssembly (Wasm).

Why Cloudflare Workers?

One of our goals with this rebuild was to reduce the amount of operational effort it takes to maintain our hosted services, so that we can focus more of our time and energy on building Zed itself.

Cloudflare Workers allow us to easily scale up to meet demand without having to fuss over it too much.

Additionally, Cloudflare offers an ever-growing amount of managed services that cover anything you might need for a production web service. Here are some of the Cloudflare services we’re using today:

• Hyperdrive for talking to Postgres
• Workers KV for ephemeral storage
• Cloudflare Queues for asynchronous job processing

The Platform

Another one of our goals with this rebuild was to build a platform that was easy to test. To achieve this, we built our own platform framework on top of the Cloudflare Workers runtime APIs.

At the heart of this framework is the Platform trait:

pub trait Platform: Sized + Clone + 'static {
type Cache: cache::Cache;
type Clock: Clock;
type KvStore: KvStore<Self>;
type ServiceBinding: Fetcher<Self>;
type DurableObjectNamespace: durable_object::DurableObjectNamespace<Self>;
type DurableObjectStub: durable_object::DurableObjectStub<Self>;
type DurableObjectState: durable_object::DurableObjectState<Self>;
type RateLimiter: rate_limiter::RateLimiter<Self>;
type SqlStorage: sql::SqlStorage;
type PostgresConnection<T>: postgres::PostgresConnection<Self, T>;
type PostgresTransaction<T>: postgres::PostgresTransaction<Self, T>;
type ExecutionContext: ExecutionContext + Clone + Unpin;
type Environment: Environment<Self> + Clone + Unpin;
type ClientWebSocket: websocket::ClientWebSocket;
type ServerWebSocket: websocket::ServerWebSocket<Self>;
type WebSocketReceiver: websocket::WebSocketReceiver;
type WebSocketSender: websocket::WebSocketSender;
type HttpClient: http_client::HttpClient<Platform = Self>;
type Queue<T: Serialize + 'static>: queue::Queue<Self, T>;
type RawQueueMessageBatch: queue::RawQueueMessageBatch<Self>;
type QueueMessageBatch<T: DeserializeOwned + 'static>: queue::QueueMessageBatch<Self, T>;
type QueueMessage<T: DeserializeOwned + 'static>: queue::QueueMessage<Self, T>;
type Rng: Clone + RngCore;

fn websocket_pair() -> Result<(Self::ClientWebSocket, Self::ServerWebSocket)>;
}

This trait allows us to write our code in a platform-agnostic way while still leveraging all of the functionality that Cloudflare Workers has to offer. Each one of these associated types corresponds to some aspect of the platform that we’ll want to have control over in a test environment.

For instance, if we have a service that needs to interact with the system clock and a Workers KV store, we would define it like this:

pub struct BillingService<P: Platform> {
clock: P::Clock,
kv_store: P::KvStore,
}

Two platforms, both alike in dignity

There are two implementors of the Platform trait: CloudflarePlatform and SimulatedPlatform.

CloudflarePlatform

CloudflarePlatform—as the name might suggest—is an implementation of the platform on top of the Cloudflare Workers runtime. This implementation targets Wasm and is what we run when developing locally (using Wrangler) and in production.

We have a cloudflare_bindings crate2 that contains wasm_bindgen bindings to the Cloudflare Workers JS runtime. You can think of CloudflarePlatform as the glue between those bindings and the idiomatic Rust APIs exposed by the Platform trait.

SimulatedPlatform

The SimulatedPlatform is used when running tests, and allows for simulating almost every part of the system in order to effectively test our code.

Here’s an example of a test for ingesting a webhook from Orb:

#[test]
fn test_orb_webhook_ingestion() {
Simulator::once(|simulator| async move {
let test_ctx = OrbWebhooksTestContext::init(&simulator).await?;

// Some more test setup...

let request = make_orb_webhook_request(
HANDLE_ORB_WEBHOOK_URL,
&webhook_event,
"2025-09-10T18:16:06.483Z".parse().unwrap(),
&test_ctx.config.orb_webhook_signing_secret,
)?;

let response = test_ctx.worker.fetch(request).await?;
assert_eq!(response.status, StatusCode::OK);

simulator.scheduler.run()?;

let updated_billing_subscription = BillingSubscriptionRepository
.find(&test_ctx.app_database, billing_subscription.id)
.await?;
assert_eq!(
updated_billing_subscription.kind,
Some(app_database::SubscriptionKind::TokenBasedZedPro)
);
assert_eq!(
updated_billing_subscription.orb_subscription_status,
Some(app_database::OrbSubscriptionStatus::Active)
);
})
.unwrap();
}

In this test we’re able to test the full end-to-end flow of:

1. Receiving and validating an incoming webhook event to our webhook ingestion endpoint
2. Putting the webhook event into a queue
3. Consuming the webhook event in a background worker and processing it

The call to simulator.scheduler.run()? advances the test simulator, in this case running the pending queue consumers.

At the center of the SimulatedPlatform is the scheduler, a crate that powers our in-house async runtime. The scheduler is shared between GPUI—Zed’s UI framework—and the Simulator used in tests.

This shared scheduler enables us to write tests that span the client and the server. So we can have a test that starts in a piece of Zed code, flows through Zed Cloud, and then asserts on the state of something in Zed after it receives the response from the backend.

Where we’re headed

The work being done on Zed Cloud now is laying the foundation to support our future work around collaborative coding with DeltaDB.

If you want to work with me on building out Zed Cloud, we are currently hiring for this role.

We’re looking for engineers with experience building and maintaining web APIs and platforms, solid web fundamentals, and who are excited about Rust.

If you end up applying, you can mention this blog post in your application.

I look forward to hearing from you!

1

The codebase is currently 70k lines of Rust code and 5.7k lines of TypeScript.

2

This is essentially our own version of worker-sys. I’d like to switch to using worker-sys directly, at some point.