rewait: wait for things properly

Written from a café in Berlin, which is why this post is stamped CEST — the blog supports per-post timezones because I refuse to lie about when things happened.

Every containerized project hits the same wall: the app boots faster than the database, crashes, and someone adds sleep 5 to the entrypoint. Then sleep 10. rewait is the grown-up version:

import { rewait, http, tcp } from "rewait";

await rewait([
  http("http://localhost:8080/healthz"),
  tcp("localhost", 5432),
], {
  timeout: 30_000,
  interval: 250,
});

It resolves when everything is up, or throws when the timeout hits. Checks run in parallel, retry on an interval, and you can hand it any async function as a custom check:

const migrated = async () => {
  const { rows } = await db.query("select 1 from schema_migrations limit 1");
  if (!rows.length) throw new Error("not migrated yet");
};

await rewait([tcp("localhost", 5432), migrated]);

The design rule I kept: checks are just functions that throw. No plugin API, no config schema, no DSL. The built-ins (http, tcp, socket, file) are conveniences that return such functions.

sleep 5 will outlive us all. But my containers boot in the right order.