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Reverse proxy: allow only one client

Posted by petsneakers 
Reverse proxy: allow only one client
June 21, 2023 06:47PM
This may sound like an odd request :-)

Is there a configuration that would limit the number of clients connecting to an nginx reverse proxy to 1? Note:

- clients are connecting through a load balancer, the reverse proxy will have access to the client ip address via the `X-Forwarded-For` header.
- number of connections should not be limited, just that there should be one originating IP address proxied at any given time.
- the client will establish a long-running websocket connection with the upstream server and as such prevent other clients from connecting to the proxy . . . this is intended.


Edited 1 time(s). Last edit at 06/21/2023 06:52PM by petsneakers.
Re: Reverse proxy: allow only one client
June 22, 2023 01:23AM
Same question with an incorrect answer:


Edited 1 time(s). Last edit at 06/22/2023 01:23AM by petsneakers.
Re: Reverse proxy: allow only one client
June 22, 2023 04:10AM
My use case could be satisfied by something like

- If a client makes an upgrade request
- Check if there is already an established websocket connection upstream
- And if so, return a 503

(I get this would allow multiple clients to make non-websocket requests, that's okay in my case.)

Is this something that njs scripting can tackle? Just learning about that now . . . maybe use the filesystem module to

- set a variable (e.g., num_ws_conns) to 1 when an upgrade connection is established (i.e., first websocket connection upstream)
- on subsequent upgrade requests check num_ws_conns and if greater than 0, 503 the request
- set num_ws_conns to 0 when the websocket request is closed

Just spitballing here . . . would appreciate feedabck if this is a reasonable approach, pointers welcome!
Re: Reverse proxy: allow only one client
June 23, 2023 05:47AM
I got something very close but wasn't sure how to reliably release the association (i.e., hook into a connection closed type of event).

Anyway, I think this is much more easily solved further upstream by getting rid of the load balancer and assigning nginx proxies to clients dynamically in the main proxy.
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