Modified health-check to allow Docker to cycle the process automatically

Dockerfile

@@ -1,4 +1,4 @@
-FROM node:9-alpine
+FROM node:12-alpine
 
 # Build-time
 RUN set -ex \
@@ -13,8 +13,9 @@ RUN chown -R app /usr/charts-server
 USER app
 
 ENV ACCEPT_HIGHCHARTS_LICENSE YES
-ENV HIGHCHARTS_VERSION latest
 ENV HIGHCHARTS_USE_STYLED NO
+ENV SERVER_CYCLE_MINUTES 720
+ENV HIGHCHARTS_VERSION "6.2.0"
 RUN npm install
 
 USER root

lib/server.js

@@ -92,8 +92,26 @@ app.use(bodyParser.json({ limit: '50mb' }));
 
 app.use('/charts', express.static('tmp/'));
 
+var SERVER_CYCLE_MINUTES = parseInt(process.env['SERVER_CYCLE_MINUTES'], 10);
+
+if (!SERVER_CYCLE_MINUTES || isNaN(SERVER_CYCLE_MINUTES)) {
+    console.error(`You must specify SERVER_CYCLE_MINUTES in the environment!`);
+    process.exit(1);
+}
+
+var UPTIME_CUT_OFF = SERVER_CYCLE_MINUTES * 60 * 1000;
+var UPTIME_RANDOM_VARIATION_CAP = Math.floor(Math.random() * 10 * 60 * 1000); // 0-10 minutes grace
+
+var serverStartTime = Date.now();
+
 app.get('/health', function (req, res) {
-    res.send('OK');
+    var uptime = Date.now() - serverStartTime;
+    if (uptime < UPTIME_RANDOM_VARIATION_CAP + UPTIME_CUT_OFF) {
+        res.send('OK for ' + uptime + 'ms');
+    } else {
+        res.status(503);
+        res.send('Server has been up too long (' + uptime + 'ms)');
+    }
 });
 
 function enableRateLimiting(options) {