Enable Fastboot and run its Node server from Procfile

USE_FASTBOOT environment variable is used to enable Fastboot.
The number of workers configurable through WEB_CONCURRENCY.

https://devcenter.heroku.com/articles/node-memory-use#running-multiple-processes

Procfile

@@ -1,3 +1,3 @@
 release: bin/diesel migration run
-web: bin/start-nginx ./target/release/server
+web: ./script/start-web.sh
 background_worker: ./target/release/background-worker

config/environment.js

@@ -22,6 +22,10 @@ module.exports = function(environment) {
       // Here you can pass flags/options to your application instance
       // when it is created
     },
+
+    fastboot: {
+      hostWhitelist: ['crates.io', /^localhost:\d+$/, /\.herokuapp\.com$/],
+    },
   };
 
   if (environment === 'development') {

config/nginx.conf.erb

@@ -64,6 +64,13 @@ http {
 			proxy_pass http://app_server;
 		}
 
+		<% if ENV['USE_FASTBOOT'] %>
+		# Just in case, only forward "/policies" to Ember for a moment
+		location = /policies {
+			proxy_pass http://localhost:9000;
+		}
+		<% end %>
+
 		location ~ ^/api/v./crates/new$ {
 			proxy_pass http://app_server;
 

fastboot.js

@@ -0,0 +1,62 @@
+/* eslint-disable no-console */
+
+'use strict';
+
+const fs = require('fs');
+const os = require('os');
+const FastBootAppServer = require('fastboot-app-server');
+
+// because fastboot-app-server uses cluster, but it might change in future
+const cluster = require('cluster');
+
+class LoggerWithoutTimestamp {
+  constructor() {
+    this.prefix = cluster.isMaster ? 'master' : 'worker';
+  }
+  writeLine() {
+    this._write('info', Array.prototype.slice.apply(arguments));
+  }
+
+  writeError() {
+    this._write('error', Array.prototype.slice.apply(arguments));
+  }
+
+  _write(level, args) {
+    args[0] = `[${level}][${this.prefix}] ${args[0]}`;
+    console.log.apply(console, args);
+  }
+}
+
+function writeAppInitializedWhenReady(logger) {
+  let timeout;
+
+  timeout = setInterval(function() {
+    logger.writeLine('waiting backend');
+    if (fs.existsSync('/tmp/backend-initialized')) {
+      logger.writeLine('backend is up. let heroku know the app is ready');
+      fs.writeFileSync('/tmp/app-initialized', 'hello');
+      clearInterval(timeout);
+    } else {
+      logger.writeLine('backend is still not up');
+    }
+  }, 1000);
+}
+
+var logger = new LoggerWithoutTimestamp();
+
+logger.writeLine(`${os.cpus().length} cores available`);
+
+let workerCount = process.env.WEB_CONCURRENCY || 1;
+
+let server = new FastBootAppServer({
+  distPath: 'dist',
+  port: 9000,
+  ui: logger,
+  workerCount: workerCount,
+});
+
+if (!cluster.isWorker) {
+  writeAppInitializedWhenReady(logger);
+}
+
+server.start();

package.json

@@ -21,10 +21,10 @@
     "lint:js": "eslint . --cache",
     "lint:deps": "ember dependency-lint",
     "prettier": "prettier --write '{app,tests,mirage}/**/*.js'",
-    "start": "FASTBOOT_DISABLED=true ember serve",
-    "start:live": "FASTBOOT_DISABLED=true ember serve --proxy https://crates.io",
-    "start:local": "FASTBOOT_DISABLED=true ember serve --proxy http://127.0.0.1:8888",
-    "start:staging": "FASTBOOT_DISABLED=true ember serve --proxy https://staging-crates-io.herokuapp.com",
+    "start": "./script/ember.sh serve",
+    "start:live": "./script/ember.sh serve --proxy https://crates.io",
+    "start:local": "./script/ember.sh serve --proxy http://127.0.0.1:8888",
+    "start:staging": "./script/ember.sh serve --proxy https://staging-crates-io.herokuapp.com",
     "test": "ember exam --split=2 --parallel",
     "test-coverage": "COVERAGE=true npm run test && ember coverage-merge && rm -rf coverage_* coverage/coverage-summary.json && nyc report"
   },

script/ember.sh

@@ -0,0 +1,12 @@
+#! /bin/sh
+set -ue
+
+export FASTBOOT_DISABLED
+
+if [ "${USE_FASTBOOT:-0}" = '1' ]; then
+    unset FASTBOOT_DISABLED
+else
+    FASTBOOT_DISABLED=1
+fi
+
+ember "$@"

script/start-web.sh

@@ -0,0 +1,12 @@
+#! /bin/sh
+set -ue
+
+if [ "${USE_FASTBOOT:-0}" = 1 ]; then
+    export USE_FASTBOOT=1
+    node --optimize_for_size --max_old_space_size=200 fastboot.js &
+    bin/start-nginx ./target/release/server &
+    wait -n
+else
+    unset USE_FASTBOOT
+    bin/start-nginx ./target/release/server
+fi

src/bin/server.rs

@@ -39,6 +39,8 @@ fn main() {
     boot::categories::sync(categories_toml).unwrap();
 
     let heroku = dotenv::var("HEROKU").is_ok();
+    let fastboot = dotenv::var("USE_FASTBOOT").is_ok();
+
     let port = if heroku {
         8888
     } else {
@@ -102,8 +104,13 @@ fn main() {
     // Creating this file tells heroku to tell nginx that the application is ready
     // to receive traffic.
     if heroku {
-        println!("Writing to /tmp/app-initialized");
-        File::create("/tmp/app-initialized").unwrap();
+        let path = if fastboot {
+            "/tmp/backend-initialized"
+        } else {
+            "/tmp/app-initialized"
+        };
+        println!("Writing to {}", path);
+        File::create(path).unwrap();
     }
 
     // Block the main thread until the server has shutdown