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End-to-End Safety

Eventual is designed to provide an end-to-end type-safe and schema-safe experience for building distributed systems with TypeScript.

  • Type-Safety can catch simple errors all the way from a: consumer of a frontend → service implementation → infrastructure configuration.
  • Schema-Safety ensures valid data is passed to APIs and Events by either attaching schemas to an API Gateway or performing runtime validation internally.

Type-Safety​

Frontend → Service​

With the ServiceClient, you can call Commands directly from your frontend (or another service) without generating code.

Import the types of your backend, create a ServiceClient and start calling commands.

import type * as MyService from "@my/service";

const client = new ServiceClient<typeof MyService>({
  serviceUrl: "your-url",
});

// type-safe interaction with commands (no code gen)
await client.hello("my name");
info

See the ServiceClient documentation for usage details.

Service → Infrastructure​

The same goes for when you’re configuring infrastructure. Import the types of the backend and then safely customize and integrate with each of the pieces of generated infrastructure.

import type * as MyService from "@my/service";

const service = new Service<typeof MyService>(this, "Service", {
  commands: {
    // safely configure any of the commands
    hello: {
      environment: { .. }
    }
  }
});

// safely access any generated infrastructure

// such as the hello Command's Lambda Function
service.commands.hello;

// or a Subscription's dead letter queue
service.subscriptions.onHelloEvent.deadLetterQueue

Schema-Safety​

Eventual integrates with Zod for defining schemas.

Schemas can be attached to Commands

export const helloCommand = command(
  "hello",
  {
    input: z.string(),
    output: z.string(),
  },
  async (name) => `hello ${name}`
);

... and Events.

export const helloEvent = event(
  "HelloEvent",
  z.object({
    name: z.string(),
  })
);

These schemas are then used to generate specifications such as JSON Schema and Open API and perform runtime validation.