Deploying Dash app to Heroku: error code=H10, H13

Question

This is my first time deploying an app to Heroku. I built a Dash app in Python that works fine in localhost and I was able to successfully build and deploy it on Heroku following tutorials for Dash though the application doesn't load when I try to launch it (instead it produces errors in logs).

I am using a Windows machine and also had to add and use this custom build pack ([located here][1]) to use Git LFS as one of my data files is too large to fit on the Git repository.

I have created a Procfile:

web: gunicorn app:server

and installed/added gunicorn to requirements.txt

I'm getting these application errors when I try to launch the app after the build is successfully completed.

2020-05-27T03:43:30.000000+00:00 app[api]: Build succeeded
2020-05-27T03:50:00.231102+00:00 heroku[web.1]: State changed from crashed to starting
2020-05-27T03:50:30.788014+00:00 heroku[web.1]: Starting process with command `gunicorn app:server`
2020-05-27T03:50:34.709044+00:00 app[web.1]: [2020-05-27 03:50:34 +0000] [4] [INFO] Starting gunicorn 20.0.4
2020-05-27T03:50:34.710044+00:00 app[web.1]: [2020-05-27 03:50:34 +0000] [4] [INFO] Listening at: http://0.0.0.0:37455 (4)
2020-05-27T03:50:34.710172+00:00 app[web.1]: [2020-05-27 03:50:34 +0000] [4] [INFO] Using worker: sync
2020-05-27T03:50:34.715383+00:00 app[web.1]: [2020-05-27 03:50:34 +0000] [10] [INFO] Booting worker with pid: 10
2020-05-27T03:50:34.720666+00:00 app[web.1]: [2020-05-27 03:50:34 +0000] [11] [INFO] Booting worker with pid: 11
2020-05-27T03:50:35.355566+00:00 heroku[web.1]: State changed from starting to up
2020-05-27T03:50:56.465384+00:00 heroku[web.1]: Process running mem=1280M(250.0%)
2020-05-27T03:50:56.493628+00:00 heroku[web.1]: Error R15 (Memory quota vastly exceeded)
2020-05-27T03:50:56.496502+00:00 heroku[web.1]: Stopping process with SIGKILL
2020-05-27T03:50:56.653528+00:00 heroku[web.1]: Process exited with status 137
2020-05-27T03:50:56.689016+00:00 heroku[web.1]: State changed from up to crashed
2020-05-27T03:50:56.575446+00:00 heroku[router]: at=error code=H13 desc="Connection closed without response" method=GET path="/" host=####.herokuapp.com request_id=56fd4ef7-74a1-4142-9637
-e76cb6a078f6 fwd="155.33.132.49" dyno=web.1 connect=0ms service=19725ms status=503 bytes=0 protocol=https
2020-05-27T03:51:01.934855+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/favicon.ico" host=####.herokuapp.com request_id=1c984ec2-5f22-4620-b3c5-34957d287d0
f fwd="155.33.132.49" dyno=web.1 connect=5000ms service= status=503 bytes= protocol=https

I'm not able to make much sense of the output from the log so I'm quite stuck as to things to troubleshoot or try.

Answer 1

Some clarification on Heroku errors:

Error R15: the memory of your application exceeds 200% of allowed memory.
Error H13: a process in your dyno opens a connection but closes it before anything is written to it.
Error H10: app crashed and is shutting down.

---

So what's happening with your application?
It's clear that you're overloading the memory of your dyno, causing the connection to immediately close and the app to crash.

Solutions:

• Consider scaling up your dynos (at least to debug and see if your app works with larger available memory).
• Offload the data from your application, store it in a database and dynamically retrieve as needed.