health check setup (GoogleChrome#1289)

Author: Sam Thorogood

app.yaml

@@ -18,3 +18,11 @@ handlers:
   script: auto
   secure: always
   redirect_http_response_code: 301
+
+readiness_check:
+  path: "/_check"
+  check_interval_sec: 5
+  timeout_sec: 4
+  failure_threshold: 2
+  success_threshold: 2
+  app_start_timeout_sec: 300

package-lock.json

@@ -57,6 +57,7 @@
     "gulp-imagemin": "^7.1.0",
     "html-minifier": "^4.0.0",
     "js-cookie": "^2.2.1",
+    "js-yaml": "^4.1.0",
     "lit-element": "^2.4.0",
     "lit-html": "^1.3.0",
     "node-fetch": "^2.6.0",
@@ -94,7 +95,6 @@
     "husky": "^4.3.0",
     "install": "^0.13.0",
     "iso-639-1": "^2.1.4",
-    "js-yaml": "^4.1.0",
     "lodash.get": "^4.4.2",
     "markdown-it": "^12.0.1",
     "markdown-it-anchor": "^8.1.2",

package.json

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2021 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// Included for types only.
+// eslint-disable-next-line no-unused-vars
+const express = require('express');
+
+/**
+ * @type {express.RequestHandler}
+ */
+const healthCheckHandler = (req, res, next) => {
+  if (req.url === '/_check') {
+    res.send('Ok');
+    return res.end();
+  }
+  return next();
+};
+
+module.exports = healthCheckHandler;

server/health-check.js

@@ -21,6 +21,7 @@ const {notFoundHandler} = require('./not-found');
 const {buildRedirectHandler} = require('./redirect');
 const {buildUniqueRedirectHandler} = require('./unique-redirect');
 const unknownDomainRedirectHandler = require('./unknown-domain');
+const healthCheckHandler = require('./health-check');
 
 const app = express();
 
@@ -63,6 +64,7 @@ const handlers = [
   ...staticPaths.map(staticPath => express.static(staticPath)),
   redirectHandler,
   uniqueRedirectHandler,
+  healthCheckHandler,
   notFoundHandler,
 ];