On 19.06.25 15:29, Brendan Kearney wrote:
i am trying to setup a transparent or intercept proxy, where a client does not know or is not configured to use a proxy, but winds up going through squid instances.  i have an iptables firewall, and can perform DNAT,

DNAT is dangerous, because the proxy on remote machine loses the real IP the connection was directed to. You need to use policy routing, where you forward packets on other host which will intercept the connections itself.

to point the traffic at a haproxy VIP.  the haproxy VIP will use least-conn load balancing to pick which of my 3 squid instances to send the traffic to.  i would like to configure the squid instances to handle the traffic coming in this way.

i am unclear as to the differences between intercept and tproxy, so some clarity there would be helpful.

"intercept" intercepts connection to remote hosts and handles it (and replies) locally. The proxy fakes being the destination server to the client.

"tproxy" does the same, but even changes the client's IP, as if the connection came from client
The proxy fakes being the client to the server (in addition to the above).

You don't need tproxy if your clients and proxy are behind NAT, translating to the same IP.

i believe transparent requires that the NAT'ing be done "on-box" as opposed to across the network by my router.  is this accurate?  are there any other differences?  which is the appropriate mechanism for my use case?

Again, don't to DNAT.

If you redirect HTTP connections on your router to the proxy, use policy routing and do intercept on the proxy.

the connection chain would look something like this:

client -> router (DNAT to VIP) -> haproxy VIP (port 3129, SNAT to VIP IP) -> squid (port 3129) -> internet

is this kind of config viable, and if so, what pieces do i have wrong?  in this scenario is transparent or intercept the proper means within squid?

You need to find out how HAPROXY handles intercepted connections.
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