add better Heroku compatibility (#2352)

* use Node/NPM semver range

* use procfile for Heroku auto-deploys

* add Heroku default for empty SERVER_URL

* update README

Procfile

@@ -0,0 +1 @@
+web: npm run build:all && node server.js

README.md

@@ -199,12 +199,8 @@ Firefox Monitor Breach Alerts is designed with [12-factor](https://12factor.net/
 
 ### Deploy on Heroku
 
-You will need to set some required environment variables on Heroku.
+We use Heroku apps for dev review only – official stage and production apps are built by the Dockerfile and CircleCI config, with deploy overseen by the Site Reliability Engineering team.
 
-```sh
-heroku config:set COOKIE_SECRET=unsafe-cookie-secret-for-heroku
-heroku config:set DEBUG_DUMMY_SMTP=1
-```
+Deploys from the `main` branch to Heroku are automatic.  We also employ Heroku's "Review Apps" to check Pull Requests.  These are currently set to auto-deploy: you can find the app link in your GitHub Pull Request. Review apps auto-destroy after 2 days of inactivity.
 
-And any others, depending on the features you're running on Heroku - e.g.,
-Email or Firefox Accounts.
+If you encounter issues with Heroku deploys, be sure to check your environment variables, including those required in `app-constants.js`.  Review apps also share a database and you should not assume good data integrity if testing db-related features.

app-constants.js

@@ -5,6 +5,10 @@
 const path = require("path");
 require("dotenv").config({path: path.join(__dirname, ".env")});
 
+if (!process.env.SERVER_URL && process.env.NODE_ENV === "heroku") {
+  process.env.SERVER_URL = `https://${process.env.HEROKU_APP_NAME}.herokuapp.com`;
+}
+
 const kEnvironmentVariables = [
   "NODE_ENV",
   "SERVER_URL",

package.json

@@ -75,8 +75,8 @@
     "sass": "^1.42.1"
   },
   "engines": {
-    "node": "14.17",
-    "npm": "6"
+    "node": "14.17.x",
+    "npm": "6.x"
   },
   "homepage": "https://github.com/mozilla/blurts-server",
   "license": "MPL-2.0",