Using the ACL in HAProxy for Load Balancing Named Virtual Hosts
Until recently, I wasn’t aware of the ACL system in HAProxy, but once I found it I realized that I have been missing a very important part of load balancing with HAProxy!
While the full configuration settings available for the ACL are listed in the configuration doc, the below example includes the basics that you’ll need to build an HAProxy load balancer that supports multiple host headers.
Here is a quick example haproxy configuration file that uses ACLs:
global
log 127.0.0.1 local0
log 127.0.0.1 local1 notice
maxconn 4096
user haproxy
group haproxy
daemon
defaults
log global
mode http
option httplog
option dontlognull
retries 3
option redispatch
maxconn 2000
contimeout 5000
clitimeout 50000
srvtimeout 50000
frontend http-in
bind *:80
acl is_www_example_com hdr_end(host) -i example.com
acl is_www_domain_com hdr_end(host) -i domain.com
use_backend www_example_com if is_www_example_com
use_backend www_domain_com if is_www_domain_com
default_backend www_example_com
backend www_example_com
balance roundrobin
cookie SERVERID insert nocache indirect
option httpchk HEAD /check.txt HTTP/1.0
option httpclose
option forwardfor
server Server1 10.1.1.1:80 cookie Server1
server Server2 10.1.1.2:80 cookie Server2
backend www_domain_com
balance roundrobin
cookie SERVERID insert nocache indirect
option httpchk HEAD /check.txt HTTP/1.0
option httpclose
option forwardfor
server Server1 192.168.5.1:80 cookie Server1
server Server2 192.168.5.2:80 cookie Server2
In HAProxy 1.3, the ACL rules are placed in a “frontend” and (depending on the logic) the request is proxied through to any number of “backends”. You’ll notice in our frontend entitled “http-in” that I’m checking the host header using the hdr_end feature. This feature performs a simple check on the host header to see if it ends with the provided argument.
You can find the rest of the Layer 7 matching options by searching for “7.5.3. Matching at Layer 7″ in the configuration doc I linked to above. A few of the options I didn’t use but you might find useful are path_beg, path_end, path_sub, path_reg, url_beg, url_end, url_sub, and url_reg. The *_reg commands allow you to perform RegEx matching on the url/path, but there is the usual performance consideration you need to make for RegEx (especially since this is a load balancer).
The first “use_backend” that matches a request will be used, and if none are matched, then HAProxy will use the “default_backend”. You can also combine ACL rules in the “use_backend” statements to match one or more rules. See the configuration doc for more helpful info.
If you’re looking to use HAProxy with SSL, that requires a different approach, and I’ll blog about that soon.