Why isn't uWSGI respecting the "--http-keepalive" flag?

Question

I installed uWSGI in a Docker container running ubuntu:16.04 using the following commands:

apt-get update
apt-get install -y build-essential python-dev python-pip
pip install uwsgi

I then created a single static file:

cd /root
mkdir static
dd if=/dev/zero bs=1 count=1024 of=static/data

...and finally started uWSGI with the following command:

uwsgi \
    --buffer-size 32768 \
    --http-socket 0.0.0.0:80 \
    --processes 4 \
    --http-timeout 60 \
    --http-keepalive \
    --static-map2=/static=./

I was able to access the static file without any problems. However, despite passing the --http-keepalive option, issuing multiple requests with cURL resulted in the following output:

# curl -v 'http://myserver/static/data' -o /dev/null 'http://myserver/static/data' -o /dev/null
*   Trying 192.168.1.101...
...
> GET /static/data HTTP/1.1
> Host: 192.168.1.101:8100
> User-Agent: curl/7.47.0
> Accept: */*
> 
< HTTP/1.1 200 OK
< Content-Length: 1024
< Last-Modified: Sat, 03 Dec 2016 22:06:49 GMT
< 
{ [1024 bytes data]
100  1024  100  1024    0     0   577k      0 --:--:-- --:--:-- --:--:-- 1000k
* Connection #0 to host 192.168.1.101 left intact
* Found bundle for host 192.168.1.101: 0x563fbc855630 [can pipeline]
* Connection 0 seems to be dead!
* Closing connection 0
...

Of particular interest is the line:

* Connection 0 seems to be dead!

This was confirmed with WireShark:

As you can see, there are two completely separate TCP connections. The first one is closed by uWSGI (packet #10 - the [FIN, ACK]).

What am I doing wrong? Why doesn't uWSGI honor the --http-keepalive flag instead of immediately closing the connection?

Answer 1

I was finally able to get keepalive working by switching from --http-socket to simply --http. According to uWSGI docs:

If your web server does not support the uwsgi protocol but is able to speak to upstream HTTP proxies, or if you are using a service like Webfaction or Heroku to host your application, you can use http-socket. If you plan to expose your app to the world with uWSGI only, use the http option instead, as the router/proxy/load-balancer will then be your shield.

In my particular case, it was also necessary to load the http plugin.