Google App Engine在Python / Flask API上产生502错误

Question

I've been all over google, and stack and read EVERY article I could find but have not been able to solve me issue. I recently wanted to take my project that is still in development and get it up on GAE so I could test it and make sure it would work as I assumed. After some trail and error I was able to get a Postgres database setup and push my project using

gcloud app deploy app.yaml

My Flask app is using Swagger and Flask-Restplus for the API. I can access the swagger page and perform some requests, however all of those requests come back with

502 Bad Gatway

While reading the live log in the console I can see the data is coming in as I would expect. There are no exceptions, and the GAE error console does not even log the 502 error. In the console I can also see..

[CRITICAL] WORKER TIMEOUT (pid:17)

So I went into the logs and see this NGINX error..

textPayload:  "[error] 32#32: *4086 upstream prematurely closed connection while reading response header from upstream, client: 130.211.2.231, server: , request: "POST /auth/login_user HTTP/1.1", upstream: "http://172.17.0.1:8080/auth/login_user", host: "blah-191811.appspot.com", referrer: "http://blah-191811.appspot.com/""  

I don't think it is an error connecting to my database because I can connect to the Postgres DB hosted on GAE from my local computer. I also have another API endpoint that just uses a google API to retrieve some info and that also produces a 502 error.

I am at my wits end, and honestly about to throw in the towel and try to get it going on AWS if I can't figure this out. Any help would be much appreciated.

EDIT WITH MORE INFO:

The problem still persists. However, I have two routes on my API that require a valid JWT header. When using these routes with an invalid header token, or no token the API returns the correct response, a 401. When sending the correct token the API again returns a 502. This makes me believe that there is nothing wrong with my code, but that somewhere the response is not getting sent back.

I should add that these are not data intensive calls. The login_user is just two strings, an email and a password. The database has only one entry in it.

When I run locally but CONNECT to the remote Postgres database the API works as expected. Ie if I run a Flask server locally and do; 127.0.0.1:5000/auth/login_user and send the correct information, it is able to read back from my Postgres database on my GAE project. So I don't believe the database is the issue either.

Still looking for any wisdom because this seems to be a very common issue with little resolve.

Answer 1

For anyone else experiencing this issue..I found the solution after much digging. It was in the way I was connecting to the potgres SQL instance on GAE.

I was using this;

SQLALCHEMY_DATABASE_URI = 'postgresql://user:password@remote.ip.addr/database_name'

This code works fine when you are accessing the SQL instance from a whitelisted IP. However this code will not work inside an instance that also runs on GAE. You need to change it to this;

SQLALCHEMY_DATABASE_URI = 'postgresql://user:password@/database_name?
host=/cloudsql/database_instance_id'