react-express-mysql: split backend code

Signed-off-by: Jérémie Drouet <jeremie.drouet@gmail.com>

react-express-mysql/backend/src/config.js

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+// Constants
+module.exports = {
+  port: process.env.PORT || 8080
+  // if you're not using docker-compose for local development, this will default to 8080
+  // to prevent non-root permission problems with 80. Dockerfile is set to make this 80
+  // because containers don't have that issue :)
+};

react-express-mysql/backend/src/index.js

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+const app = require("./server");
+const { port } = require("./config");
+
+const server = app.listen(port, function() {
+  console.log("Webserver is ready");
+});
+
+//
+// need this in docker container to properly exit since node doesn't handle SIGINT/SIGTERM
+// this also won't work on using npm start since:
+// https://github.com/npm/npm/issues/4603
+// https://github.com/npm/npm/pull/10868
+// https://github.com/RisingStack/kubernetes-graceful-shutdown-example/blob/master/src/index.js
+// if you want to use npm then start with `docker run --init` to help, but I still don't think it's
+// a graceful shutdown of node process
+//
+
+// quit on ctrl-c when running docker in terminal
+process.on("SIGINT", function onSigint() {
+  console.info(
+    "Got SIGINT (aka ctrl-c in docker). Graceful shutdown ",
+    new Date().toISOString()
+  );
+  shutdown();
+});
+
+// quit properly on docker stop
+process.on("SIGTERM", function onSigterm() {
+  console.info(
+    "Got SIGTERM (docker container stop). Graceful shutdown ",
+    new Date().toISOString()
+  );
+  shutdown();
+});
+
+// shut down server
+function shutdown() {
+  server.close(function onServerClosed(err) {
+    if (err) {
+      console.error(err);
+      process.exit(1);
+    }
+    process.exit(0);
+  });
+}
+//
+// need above in docker container to properly exit
+//

react-express-mysql/backend/src/server.js

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+// simple node web server that displays hello world
+// optimized for Docker image
+
+const express = require("express");
+// this example uses express web framework so we know what longer build times
+// do and how Dockerfile layer ordering matters. If you mess up Dockerfile ordering
+// you'll see long build times on every code change + build. If done correctly,
+// code changes should be only a few seconds to build locally due to build cache.
+
+const morgan = require("morgan");
+// morgan provides easy logging for express, and by default it logs to stdout
+// which is a best practice in Docker. Friends don't let friends code their apps to
+// do app logging to files in containers.
+
+// Appi
+const app = express();
+
+app.use(morgan("common"));
+
+app.get("/", function(req, res) {
+  res.json({ message: "Hello Docker World!" });
+});
+
+app.get("/healthz", function(req, res) {
+  // do app logic here to determine if app is truly healthy
+  // you should return 200 if healthy, and anything else will fail
+  // if you want, you should be able to restrict this to localhost (include ipv4 and ipv6)
+  res.send("I am happy and healthy\n");
+});
+
+module.exports = app;