HAProxy Concepts

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Internal

Proxy Mode

Two major proxy modes are supported: "tcp", also known as layer 4 and "http" known as layer 7.

"tcp" Proxy Mode

In "tcp" mode, HAProxy forwards bidirectional traffic between two sides.

"http" Proxy Mode

In "http" mode, HAProxy analyzes the protocol and can interact with it by allowing, blocking, switching, adding, modifying or removing arbitrary contents in requests or responses.

Logging

http://cbonte.github.io/haproxy-dconv/1.8/management.html#8

HAProxy does not write log information on disk, but it forwards it to the syslog server, over UDP, by default on port 514.

HAProxy Logging Configuration

Connection Health Check

https://www.haproxy.com/doc/aloha/7.0/haproxy/healthchecks.html#

SSL Support

https://serversforhackers.com/using-ssl-certificates-with-haproxy

HAProxy can be configured to terminate the SSL connection or to pass it through the backend server.

SSL Termination

SSL Pass-Through

When HAProxy is configured with SSL pass-through, the backend servers handle the SSL connection, rather than the load balancer. The load balancer will just simply proxy the request off to its backend server. The connection will remain encrypted, and the load balancer cannot see what it contains. The frontend will have to be configured in "tcp" mode. For more details on configuration, see:
HAProxy SSL Pass-Through Configuration