Embedded variables from ngx_http_core_module and websocket connections

Dorin RuV ruv.donita at gmail.com
Tue Jul 20 10:39:51 UTC 2021

Hi everybody,

I'm currently having an issue with nginx which I cannot get to the bottom

I'm using nginx as a reverse proxy/load balancer in front of Kubernetes.
I'm trying to set up Websocket connections with an app running in
Kubernetes, but there are some problems. I have followed the "more
sophisticated" example from https://nginx.org/en/docs/http/websocket.html.

The configuration more or less looks like:

"http {

  map $http_upgrade $connection_upgrade {
    default upgrade;
    '' close;
  }      # building the connection_upgrade variable based on $http_upgrade

  listen 443 ssl http2;
  location / {
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection $connection_upgrade;
There is also a server { listen 80 } directive there which simply redirects
to https.

If I configure "proxy_set_header Upgrade  Websocket" and "Connection
Upgrade", everything works as intended. It seems though that the
$http_upgrade variable is seen as empty, even though tcpdump confirms the
fact that the Upgrade header is correctly sent to Nginx by the client
request. Can somebody please point me towards what could reset this
variable or why is it unavailable? I'm thinking some scope issues but I
have no idea how to debug.

Thank you!
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