Haproxy

Haproxy (Originally High Availability Proxy) provides an industrial grade proxy to the Gentoo administrator routing traffic between ones frontend (web-facing) and backend (web-servers/web-services/databases). It reports connectivity statistics, performs health checks upon backend services and supports load balancing.

Interestingly, if one has multiple frontend machines HAProxy will redirect clients from one machine to another as they are taken offline ensuring a consistent service (One stands under correction on this point).

It handles both TCP (Level 4 in the OSI model) and the HTTP (Level 7 in the OSI model) routing (Routing further protocols seems possible too e.g. mail).

SSL termination may be done at Haproxy or passed through to be termination at the backend (SNI).

Additional software
The following software supports, compliments or integrates with Haproxy :

 HATop An interactive ncurses client and real-time monitoring, statistics displaying tool for the Haproxy TCP/HTTP load balancer Herald A load feedback and check agent for Haproxy Haproxystats A statistics collector which processes various statistics and pushes them to a graphing system (Graphite) 

HAProxy serves the usual web-servers (Apache/Lighthttpd/NginX/Traefik) and databases (PostgreSQL/Redis/MySQL/CouchDB) and supports encryption (OpenSSL/LetsEncrypt). It will handle backend connections via unix and web sockets. These packages are used with haproxy and do not interact with it directly, hence are not listed here.

Configuration
The global section, within Haproxy's configuration file, specifies the services permissions and behaviour upon ones system. This file is read sequentially and one may define One or more default block(s) may be set to define the common behaviour of the subsequent frontend/backend blocks; with later default blocks overriding the earlier ones.

In the example that follow one provide the minimal configuration necessary to enable some feature provided by Haproxy. By combining these examples one should be able to configure Haproxy for their own setup.

Files
The following files and folders are used to configure Haproxy

* - The main configuration file * - The SSL certificates folder * - An alternate, possibly better, location for SSL certificates

Global
The haproxy user and group are configured by emerge during installation.

SSL
This terminates the secure connection and passes the decrypted traffic on to the backend. This assumes the backend is run on a secured internal network.

Haproxy uses a single certificate for authentication purposes, that is an ordered and combined key, thing and thing. If ones certificates are supplied by letsencrypts' certbot then they may use the following line to generate a combined certiifcate for haproxy. The combined certificates should be stored under either the Haproxy folder,, or the OpenSSL one, (The author is not sure which of these paths is the canonical one).

SNI
SNI is performed within the TCP layer (Level 4 in the OSI model) allowing frontend connections over HTTPS to be directed to the appropriate backend. Only very old browsers do not support this e.g. I.E. on WinXP.

External resources

 * https://skarlso.github.io/2017/02/15/how-to-https-with-hugo-letsencrypt-haproxy/