Add health check + error handling for mongoose connect

.prettierrc

@@ -0,0 +1,4 @@
+{
+  "singleQuote": true,
+  "trailingComma": "es5"
+}

server/db/connect.js

@@ -4,13 +4,32 @@ const mongoose = require('mongoose');
 mongoose.set('debug', false);
 mongoose.Promise = global.Promise;
 
-const MONGO_URL = process.env.MONGO_URL;
-mongoose.connect(MONGO_URL || 'mongodb://localhost/data', {
-  useMongoClient: true
-});
+const MONGO_URL = process.env.MONGO_URL || 'mongodb://localhost/data';
+const MONGO_OPT = {
+  useMongoClient: true,
+};
+
+async function connectMongo() {
+  try {
+    await mongoose.connect(MONGO_URL, MONGO_OPT);
+  } catch (err) {
+    console.log('Connect to database failed -> exiting');
+    // k8s can restart the pod
+    process.exit(-1);
+  }
+}
+connectMongo().then(() => console.log('Database connected'));
 
 const db = mongoose.connection;
 
 db.on('error', (err) => console.log('Error connecting to database: ', err));
-db.on('disconnected', (err) => console.log('Disconnected from the database: ', err));
-db.on('close', (err) => console.log('Closed the connection to the database: ', err));
+db.on('disconnected', async (err) => {
+  console.log('Disconnected from the database -> exiting: ', err);
+  // mongo/mongoose are stupid - can't retry normally. 
+  // when I try to reconnect here, it fails with  `MongooseError [OverwriteModelError]: Cannot overwrite `Place` model once compiled.`
+  // so it might be better to let k8s to restart the pod
+  process.exit(-2);
+});
+db.on('close', (err) =>
+  console.log('Closed the connection to the database: ', err)
+);

server/health-check/health-check.js

@@ -0,0 +1,29 @@
+const { getUserByEmail } = require('../service/userService');
+
+const checkMongo = async () => {
+  await getUserByEmail('[email protected]');
+};
+
+const checks = [checkMongo];
+
+const healthCheck = async (req, res) => {
+  let ok = true;
+  const response = {};
+  const performCheck = async (fn) => {
+    try {
+      await fn();
+      response[fn.name] = 'ok';
+    } catch (err) {
+      response[fn.name] = `${err}`;
+      ok = false;
+    }
+  };
+  await Promise.all(checks.map((fn) => performCheck(fn)));
+  return res.status(ok ? 200 : 500).json(response);
+};
+
+const setupHealthCheck = (app) => {
+  app.use('/health-check', healthCheck);
+};
+
+module.exports = { setupHealthCheck };

server/index.js

@@ -11,6 +11,7 @@ const cors = require('cors');
 const { setupAttendenceApi } = require('./api/attendenceApi');
 
 const exportMiddleware = require('./export/exportMiddleware');
+const { setupHealthCheck } = require('./health-check/health-check');
 
 const argv = require('minimist')(process.argv.slice(2));
 
@@ -44,6 +45,7 @@ app.use('/graphql', graphqlHTTP((req) => ({
 })));
 
 setupAttendenceApi(app);
+setupHealthCheck(app);
 
 app.use('/export/*', bodyParser.json());
 app.post('/export/*', exportMiddleware);