HAproxy
HAProxy is a free, very fast and reliable solution offering high availability, load balancing, and proxying for TCP and HTTP-based applications. It is particularly suited for very high traffic web sites and powers quite a number of the world's most visited ones. Over the years it has become the de-facto standard opensource load balancer, is now shipped with most mainstream Linux distributions, and is often deployed by default in cloud platforms.
Running
Enable haproxy.service. HAProxy's configuration can be reloaded live by reloading haproxy.service as root.
Configuration
An example configuration is available in /etc/haproxy/haproxy.cfg. Edit it to suit your needs, and then start haproxy.service.
ACLs
HAProxy supports ACLs, which can be used to test conditions and perform a given action based on the results of those tests. A typical ACL would be written as follows:
/etc/haproxy/haproxy.cfg
acl photo_page path_beg /photos
In this case, the ACL is matched if the user's request path begins with /photos.
Backends
In HAProxy terminology, backends are a server or set of servers that will receive forwarded requests. Backends can balance load based on several load balancing algorithms, including:
- Round-robin
- Static round-robin (also known as weighted round-robin)
- Least connections
An example backend may be written as follows:
/etc/haproxy/haproxy.cfg
backend http-in balance roundrobin server s1 web1.example.com:80 check server s2 web2.example.com:80 check
Frontends
Frontends are used to define how requests should be forwarded to backends. They consist of the following:
- IP addresses and ports
- ACLs
- use_backend rules
Health checks
When a backend is declared with the check option, HAProxy will check on startup and on scheduled intervals if the backend is available to process forwarded requests. If a backend fails the health check, it will be removed from rotation until it is deemed to be healthy again, i.e. it passes the health check.
By default, HAProxy will attempt to establish a TCP connection to the backend to determine healthiness.
If a large number of backends are declared with the check option, HAProxy will query all of them on startup, which may delay startup time.
Logging with systemd
To configure HAproxy to use systemd /dev/log compatibility socket add the following to your configuration file under the global section.
log /dev/log local0 info
If you use the chroot option in your global configuration, you need to bind the socket into the chroot.
For this we will use a systemd.mount(5) unit. Generate the unit name with:
# systemd-escape --suffix=mount --path /var/lib/haproxy/dev/log
We want mount /dev/log into the chroot, but just after journald came up. Create a replacement unit file:
With the mount file created it is time to expand the original service unit so it mounts up everything correctly. Use a drop-in file for haproxy.service and add:
Performing TLS/SSL termination
In order to use haproxy as a TLS terminator you have to set inside your section
bind :80 bind :443 ssl crt /path/to/combined/cert
alpn h2,http/1.1 at the end of the bind :443 line.Redirecting HTTP to HTTPS
Set in your section
redirect scheme https code 301 if !{ ssl_fc }
Virtual host like configuration
Suppose you have two backends: foo and and each should handle requests only for a specific domain.
In order to perform this in your section you can configure
use_backend foo-backend if { hdr(host) -i foo.example.com || hdr(host) -i www.foo.example.com }
use_backend bar-backend if { hdr(host) -i bar.example.com || hdr(host) -i www.bar.example.com }