Make initialization more resilient

index.js

 const https = require('https');
 const express = require('express');
-
-// Initialize
-// --------------------------------------------------------
-
-const app = express();
+const { error } = require('console');
 
 const config = require('./config');
-config.init();
-
 const db = require('./database');
-db.init();
+const knotdns = require('./knotdns');
 
-// Sync records from master
-// --------------------------------------------------------
+// number of times to try syncing DNS records from master before giving up
+const retryMax = 5;
 
-console.log("Syncing records from " + config.config().master.address + "/ ...");
 
+// Synchronizes current DNS records from master
+function syncRecords() {
+	return new Promise((resolve, reject) => {
 		https.get(config.config().master.address + '/dyndns-list?id=' + config.config().master.myId + '&key=' + config.config().master.key, (res) => {
 			if (res.statusCode > 299) {
-		process.exit(2);
+				const errormsg = 'Bad HTTP status code from ' + config.config().master.address + ' : ' + res.statusCode;
+				reject(errormsg);
 				return;
 			}
 
@@ -48,29 +45,34 @@ https.get(config.config().master.address + '/dyndns-list?id=' + config.config().
 										await knotdns.updateRecord(domain, ip);
 										console.log("Registering domain " + domain + " to " + ip);
 									}
-						};
+								}
+								resolve();
+								return;
 							}
 							loadRecords(records);
 						} catch (error) {
-					console.error("Error parsing records from master: ", error);
-					process.exit(1);
+							const errormsg = "Error parsing records from master: " + error;
+							reject(errormsg);
+							return;
 						}
 					})
 				})
 			});
 		}).on('error', (error) => {
-	console.error("Could not sync records from master: ", error);
-	process.exit(1);
+			const errormsg = "Could not sync records from master: " + error;
+			reject(errormsg);
+			return;
 		});
+	})
+}
 
-// Register and serve endpoints
-// --------------------------------------------------------
 
+// Start HTTP server and process record updates
+function handleUpdates() {
+	return new Promise((resolve, reject) => {
 		const registerMW = require('./middleware/registerMW');
 		const replyMW = require('./middleware/replyMW');
 		const updateMW = require('./middleware/updateMW');
-const { error } = require('console');
-const knotdns = require('./knotdns');
 
 		// register a new dyndns record
 		app.get('/register', registerMW(), replyMW());
@@ -82,4 +84,44 @@ const server_port = config.config().listenPort;
 		const server_domain = config.config().listenAddress;
 		app.listen(server_port, server_domain, function () {
 			console.log(`This server is listening on http://${server_domain}:${server_port}`);
+			resolve();
 		});
+	})
+}
+
+
+// Try syncing from master a few times and then serve DNS update requests
+function syncAndRun(retries) {
+	console.log("Syncing records from " + config.config().master.address + "/ ...");
+
+	syncRecords().then(() => {
+		handleUpdates();
+	})
+		.catch((errormsg) => {
+			console.error(errormsg);
+			if (retries < retryMax) {
+				console.error("Retrying in 1 min.");
+				setTimeout(() => {
+					syncAndRun(retries + 1);
+				}, 60000);
+			} else {
+				console.error("Giving up.");
+				process.exit(1);
+			}
+		})
+
+}
+
+// Initialize
+// --------------------------------------------------------
+
+const app = express();
+
+config.init();
+db.init();
+
+// Sync records from master then serve requests
+// --------------------------------------------------------
+
+var retries = 0;
+syncAndRun(retries);