How to deploy an Express API with a database.

The short answer

To deploy an Express API, give your coding agent the sentence below. Antideploy finds Express in your package.json, runs npm run start, and sends traffic to the port in the PORT variable. If your code needs Postgres, it creates a database and sets DATABASE_URL. You need three things in your code: a start script, a server that reads PORT, and a database connection that reads DATABASE_URL.

What Antideploy detects

• Express. Detected from the express dependency. Fastify, Koa, NestJS and hapi are detected the same way.
• The start command. A Procfile web: line wins. Otherwise Antideploy runs your start script with npm run start. Without either, it cannot tell how to run the app and says so.
• The port. It starts your app with PORT set. Your code must use it.
• The versions. The Node.js version comes from engines.node in package.json, a .nvmrc or a .node-version file.
• The database. A pg, postgres, @neondatabase/serverless or @vercel/postgres dependency, or Prisma or Drizzle, means Postgres.

What your code needs

import express from "express";
import pg from "pg";

const app = express();
const pool = new pg.Pool({ connectionString: process.env.DATABASE_URL });

app.get("/health", (req, res) => res.send("ok"));

const port = process.env.PORT || 3000;
app.listen(port, "0.0.0.0");

{
  "scripts": { "start": "node server.js" }
}

If you write TypeScript, add a build script that compiles it and point start at the compiled file, for example node dist/server.js. A start script that needs a tool kept only in devDependencies, such as tsx or ts-node, can fail, because development dependencies are removed from the image after the build.

Step by step

1. Check the three things

   Your project has a start script, the server reads PORT, and the database is read from DATABASE_URL.

2. Paste the sentence and approve one link

   Your agent creates the app, and a Postgres database if your code needs one, and writes the connection details into your .env without printing them. The same database serves local testing and the live app.

3. Deploy and open the link

   Antideploy installs with npm ci when there is a package-lock.json, runs your build, runs your migration command if it found one, starts the app, checks that it answers and opens it.

Migrations

If you use an ORM with migrations, Antideploy detects the command and runs it before the new version goes live. A failed migration fails the deploy, so a broken schema never goes live.

• Prisma runs npx prisma migrate deploy when you have a migrations folder, and npx prisma db push when you do not
• Drizzle runs npx drizzle-kit migrate
• If a migration fails because prisma or drizzle-kit is not found, move it into dependencies in package.json

Common problems

• The app never starts listening. The server ignores PORT, or it listens on 127.0.0.1. See the full fix.
• The lock file is out of date. See npm ci can only install packages when package.json and package-lock.json are in sync.
• Data disappears after a deploy. You used SQLite or saved uploads to disk. Use Postgres and a bucket instead.
• A timer never fires. A scheduler inside the app, such as node-cron, cannot run while the app sleeps. Use a scheduled job.