Restate’s
Programming Model

Promises / Futures for RPC

Handlers can also be called directly from other Restate handlers, yielding reliable exactly-once RPC. Durable Execution journals and recovers the invocation futures/promises, deduplicating calls and memorizing responses.

You write sequential RPC code, but get async event-driven execution.

The sequential request/response code runs the reliability, scalability, and decoupling of an event-driven architecture: Restate is the message queue, durable execution acts as the persistent state machine connecting requests and responses.

Promises / Futures for Signals

Durable Promises/Futures can be used as conditions and signals, and completed via webhooks, events, other handlers, human approval, etc. They work across processes boundaries and crashes.

const signup = workflow({
  name: "usersignup",
  handlers: {
    run: async (ctx: WorkflowContext, params: { ... }) => {
      // ...
      const secret = await ctx.run("gen secret", () => crypto.randomUUID());
      ctx.run("send email", () => sendEmailWithLink({ email, secret }));

      const clickSecret = await ctx.promise<string>("email-secret");
      if (clickSecret !== secret) {
        throw new TerminalError("verification failed");
      }
      // proceed with verification
    },

    linkClick: async (ctx: WorkflowSharedContext, secret: string) => {
      ctx.promise<string>("email-secret").resolve(secret);
    }
  }
});

const greeter = restate.object({
  name: "greeter"
  handlers: {
    greet: async (ctx: restate.ObjectContext, request: {}) => {
      const count = ctx.get<number>("count") ?? 0;
      ctx.set("count", ++count);
      return `Hello ${ctx.key} for the ${count}-th time.`;
    },
    reset: async (ctx: restate.ObjectContext, request: {}) => {
      ctx.set("count", 0);
      return `Back to zero for ${ctx.key}.`;
    }
  }
});

curl -X POST restate:8080/greeter/Sonali/greet   # Hello Sonali for the 1-th time.
curl -X POST restate:8080/greeter/Peter/greet    # Hello Peter for the 1-th time.
curl -X POST restate:8080/greeter/Sonali/greet   # Hello Sonali for the 2-th time.
curl -X POST restate:8080/greeter/Peter/reset    # Back to zero for Peter.