Not able to start sapper app in production mode

Question

As the title say, i can't start my sapper project in production mode. When i run npm run start i will get this output on console:

niklas@Niklass-iMac project-name % npm run start

> apple-on-svelte@0.0.1 start /Users/niklas/path/to/project
> node __sapper__/build

Starting server on port 3000
niklas@Niklass-iMac project-name %

as you can see the command is aborted immediately and the server is not started. What could be the cause?

my package.json looks like this

{
    "name": "project name",
    "description": "description",
    "version": "0.0.1",
    "scripts": {
        "build": "sapper build --legacy",
        "deploy": "firebase deploy --only functions",
        "dev": "sapper dev",
        "export": "sapper export --legacy",
        "fb_start": "npm run shell",
        "logs": "firebase functions:log",
        "serve": "firebase emulators:start --only functions",
        "shell": "firebase functions:shell",
        "start": "node __sapper__/build"
    },
    "browserslist": [
        "last 3 version"
    ],
    "engines": {
        "node": "10"
    },
    "dependencies": {
        "compression": "^1.7.4",
        "express": "^4.17.1",
        "firebase-admin": "^8.10.0",
        "firebase-functions": "^3.6.0",
        "sirv": "^0.4.2"
    },
    "devDependencies": {
        "@babel/core": "^7.9.0",
        "@babel/plugin-syntax-dynamic-import": "^7.8.3",
        "@babel/plugin-transform-runtime": "^7.9.0",
        "@babel/preset-env": "^7.9.5",
        "@babel/runtime": "^7.9.2",
        "@fullhuman/postcss-purgecss": "^2.1.2",
        "@rollup/plugin-commonjs": "11.0.2",
        "@rollup/plugin-node-resolve": "^7.1.3",
        "@rollup/plugin-replace": "^2.3.1",
        "autoprefixer": "^9.7.6",
        "cssnano": "^4.1.10",
        "firebase-functions-test": "^0.2.0",
        "npm-run-all": "^4.1.5",
        "postcss": "^7.0.27",
        "postcss-import": "^12.0.1",
        "postcss-nested": "^4.2.1",
        "postcss-url": "^8.0.0",
        "rollup": "^2.6.1",
        "rollup-plugin-babel": "^4.4.0",
        "rollup-plugin-postcss": "^2.6.1",
        "rollup-plugin-svelte": "^5.2.1",
        "rollup-plugin-terser": "^5.3.0",
        "sapper": "^0.27.12",
        "svelte": "^3.20.1",
        "svelte-preprocess": "^3.7.1",
        "svelte-preprocess-postcss": "^1.1.1",
        "tailwindcss": "^1.2.0"
    }
}

and my src/server.js looks like this:

import sirv from "sirv";
import express from "express";
import compression from "compression";
import * as sapper from "@sapper/server";

import "./assets/global.css";

const { PORT, NODE_ENV } = process.env;
const dev = NODE_ENV === "development";

const expressServer = express().use(
    compression({ threshold: 0 }),
    sirv("static", { dev }),
    sapper.middleware()
);

if (dev) {
    expressServer.listen(PORT, (err) => {
        if (err) console.log("error", err);
    });
}

export { expressServer };

and my index.js looks like this:

const functions = require("firebase-functions");
const { expressServer } = require("./__sapper__/build/server/server");

exports.ssr = functions.https.onRequest(expressServer);

I use rollup and the latest node lts version on macOS 10.15.5 Without problems, i can run npm run dev or npm run build, but not npm run start

How can i solve this? Any ideas?

Answer 1

As far as I can judge your express service, it seems that you don't listen to incoming connections when not in dev mode. The exact code that is responsible for this is:

// only in dev mode you listen to inc connections
if (dev) { 
    expressServer.listen(PORT, (err) => {
        if (err) console.log("error", err);
    });
}

This will skip the listing part whenever you are not in development mode. I would consider moving the if statement into your listen callback function, like:

expressServer.listen(PORT, (err) => {
    if (err && dev) console.log("error", err);
});

That should keep the server running and listing to future connections. If this helped you please leave me a small thumb up. For more information, I would also recommend you the quickstarter guide for expressJS