502 occurs when the Nginx proxy in front of your application container is not able to communicate with your application code to send it requests. This is often due to mis-configuration of your
app.yaml,
package.json, or
incorrect coding that is preventing your application from accepting request.
I would recommend taking a look at the
Getting Started samples to properly deploy a working App Engine application. Once you have a template app that can accept requests and respond to them, you can then begin to alter it for your use-case.
- Note that Google Groups is for general product discussions and not for technical support. If you require further technical support for coding an application for App Engine it is recommended to post your
full detailed question to
Stack Overflow using the supported Cloud tags.