Force SSL on App Engine Flexible Environment Custom Runtime

Question

We're running an instance of Metabase on a App Engine Flexible Custom Runtime with a Dockerfile based on openjdk:8. Currently it allows access on http://[metabase-project].appspot.com/ and https://[metabase-project].appspot.com/. I'd like to force SSL by having all http traffic redirected to https.

The Dockerfile looks something like this:

FROM openjdk:8
ADD https://dl.google.com/cloudsql/cloud_sql_proxy.linux.amd64 ./cloud_sql_proxy
ADD http://downloads.metabase.com/v0.21.1/metabase.jar ./metabase.jar
CMD ./cloud_sql_proxy -instances=$INSTANCE=tcp:$MB_DB_PORT -dir=/cloudsql & java -jar ./metabase.jar

Our app.yaml looks like:

service: metabase
runtime: custom
env: flex

In a normal App Engine app.yaml file, I'd want to add:

handlers:
- url: [something]
  secure: always

But in the custom runtime we don't have access to handlers like this. Is there a way to configure the Flexible runtime to perform the redirect for all traffic?

Answer 1

App Engine Flex doesn't support handlers, at all: https://cloud.google.com/appengine/docs/flexible/java/upgrading#appyaml_changes

If you need https:// redirects, you need to do it from within your application. Sorry!

Answer 2

Since your app (env: flex in app.yaml) is running behind an nginx reverse proxy which terminates the SSL connection, you need to check the X-FORWARDED-PROTO header which will be either http or https. If it’s http then you can do the redirect.

Answer 3

This is what worked for me. In my case using Loopback based NodeJS application running in Cloud Sites App Engine flexible environment.

1. Create a middleware, for example server/middleware/https-redirect.js with the following code:

   /**
   * Create a middleware to redirect http requests to https
   * @param {Object} options Options
   * @returns {Function} The express middleware handler
   */
   module.exports = function(options) {
     options = options || {};
     var httpsPort = options.httpsPort || 443;
     return function(req, res, next) {
       if (req.protocol != 'https' && process.env.NODE_ENV !== 'development') {
         var parts = req.get('host').split(':');
         var host = parts[0] || '127.0.0.1';
         return res.redirect('https://' + host + ':' + httpsPort + req.url);
       }
       next();
     };
   };
   

   (based on the step 8 in the post http://www.jonxie.com/blog/2014/11/12/setting-up-loopback-to-use-https-and-ssl-certificates/ but modified to use req.protocol instead of req.secure, also will only redirect if not running in development mode)

2. Modify the file server/server.js to request:

   var httpsRedirect = require('./middleware/https-redirect');
   

3. An then, after the boot line:

   var httpsPort = app.get('https-port');
   app.use(httpsRedirect({httpsPort: httpsPort}));
   app.set('trust proxy', true)
   

Setting app.set('trust proxy', true) will let the req.protocol read the X-Forwarded-Proto header.

References:

• http://expressjs.com/es/api.html#req.protocol
• http://expressjs.com/en/guide/behind-proxies.html
• http://www.jonxie.com/blog/2014/11/12/setting-up-loopback-to-use-https-and-ssl-certificates/

Answer 4

Late to answer, but I had to struggle a lot in order to do this.

I followed various links which mentioned the following code,

app.use(function(req, res, next) {
  if(!req.secure) {
    return res.redirect(['https://', req.get('Host'), req.url].join(''));
  }
  next();
});

This might work in other cloud vendors.

But in GCP as rightly mentioned by @zengabor, our app will be running behind an nginx reverse proxy which terminates the SSL connection, we need to check the X-FORWARDED-PROTO which can be done by the following code,

app.use(function(req, res, next) {
  if(req.headers['x-forwarded-proto'] && req.headers['x-forwarded-proto'] === "http") {
    return res.redirect(['https://', req.get('Host'), req.url].join(''));
  }
  next();
});

Just adding my answer as after reading @zengabor's code I had to search again on how to achieve it. So above is the readymade code which will work.