What env var to send requests to a HAProxy instance?

Question

I have a HAProxy configured that works as expected when sending requests directly to the proxy host and port that the proxy is listening on. The proxy is running in TCP mode.

frontend tcp-in-mssql
  bind :5650
  mode tcp
  use_backend mssql

backend mssql
  mode tcp
  server mssql01.mydomain.com mssql01.mydomain.com:5650 check  

When I try to send requests to the proxy by using the SOCKS_PROXY or ALL_PROXY env vars, the proxy isn't used and the connection is made directly.

example:

SOCKS_PROXY=socks://localhost:5650 my_command --target=mssql01.mydomain.com:5650
ALL_PROXY=socks://localhost:5650 my_command --target=mssql01.mydomain.com:5650

The proxy is bypassed and a TCP connection is made directly to the target host. Though if do something like my_command --target=localhost:5650 the TCP connection goes through the proxy and is made successfully to the backend target server.

How can I route traffic to the proxy?

Answer 1

Socks is a specific protocol to be spoken by client and proxy (https://en.wikipedia.org/wiki/SOCKS). Socks allows the client to specify which server to connect to on which port. To do so, the client establishes a connection to the socks proxy, the socks proxy then establishes a connection to the server and forwards the traffic from client to server and vice versa.

Example:

client -> socks proxy (port: 1080) -> server1 (port: clients choice)
                                   -> server2 (port: clients choice)
                                   -> serverN (port: clients choice)
                                   -> server (clients choice)

Your HAProxy configuration configures the haproxy to serve as a reverse proxy for tcp connections on port 5650. Tcp traffic received on port 5650 will then be forwarded to one of the destination servers configured in backend section.

Example:

client -> reverse proxy (port 5650) -> backend (server and port 
                                       as defined in haproxy config)

So you already have a working solution for proxying the connection to the mssql backend. Just configure the mssql client to connect to the hapoxy on port 5650.

If you need a socks proxy to suit your use case, you have to replace the haproxy with a dedicated, socks capable proxy solution