uwsgi + nginx + flask: upstream prematurely closed

I created an endpoint on my flask which generates a spreadsheet from a database query (remote db) and then sends it as a download in the browser. Flask doesn’t throw any errors. Uwsgi doesn’t complain.

But when I check nginx’s error.log I see a lot of

2014/12/10 05:06:24 [error] 14084#0: *239436 upstream prematurely
closed connection while reading response header from upstream, client:
34.34.34.34, server: me.com, request: “GET /download/export.csv HTTP/1.1”, upstream: “uwsgi://0.0.0.0:5002”, host: “me.com”, referrer:
“https://me.com/download/export.csv“

I deploy the uwsgi like

uwsgi --socket 0.0.0.0:5002 --buffer-size=32768 --module server --callab app

my nginx config:

server {
     listen 80;
     merge_slashes off;
     server_name me.com www.me.cpm;

     location / { try_files $uri @app; }
       location @app {
          include uwsgi_params;
          uwsgi_pass 0.0.0.0:5002;
          uwsgi_buffer_size 32k;
          uwsgi_buffers 8 32k;
          uwsgi_busy_buffers_size 32k;
     }

}

server {
      listen 443;
      merge_slashes off;
      server_name me.com www.me.com;

    location / { try_files $uri @app; }
       location @app {
          include uwsgi_params;
          uwsgi_pass 0.0.0.0:5002;
          uwsgi_buffer_size 32k;
          uwsgi_buffers 8 32k;
          uwsgi_busy_buffers_size 32k;
       }
}

Is this an nginx or uwsgi issue, or both?

Best answer

Change nginx.conf to include

sendfile        on;
client_max_body_size 20M;
keepalive_timeout  0;

See self answer uwsgi upstart on amazon linux for full example