Wt

h1. Using HAproxy as a reverse proxy

HAproxy has a great feature set when used in conjunction with Wt:

• Uses async I/O and thus handles thousands of connections without any problem. Just like Wt!
• Supports reverse proxying of WebSocket connections (as per draft-76).
• Can be configured to use session affinity without needing cookies.

h2. Basic setup

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

listen 0.0.0.0:8181
server srv1 0.0.0.0:9090 check

h2. Using session affinity

All of the built-in mechanisms in HAproxy for session affinity using the @appsession@ option rely on cookies, but cookies are not our preferred method since this does not give an intuitive user experience (e.g. a user cannot open multiple sessions), are not entirely reliable (a user can disable cookies) and a source of security risks (CSRF).

Luckily there is a work-around: using Wt's ability to generate session-id's that have a prefix which identifies the back-end, we can have HAproxy match on this prefix in the request URL and send the requests to the correct server.

Below is an example configuration for two back-end servers.

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 wt
bind 0.0.0.0:80
acl srv1 url_sub wtd=wt1
acl srv2 url_sub wtd=wt2
acl srv1_up nbsrv(bck1) gt 0
acl srv2_up nbsrv(bck2) gt 0
use_backend bck1 if srv1_up srv1
use_backend bck2 if srv2_up srv2
default_backend bck_lb

backend bck_lb
balance roundrobin
server srv1 0.0.0.0:9090 track bck1/srv1
server srv2 0.0.0.0:9091 track bck2/srv2

backend bck1
balance roundrobin
server srv1 0.0.0.0:9090 check

backend bck2
balance roundrobin
server srv2 0.0.0.0:9091 check

And start the two Wt httpd servers using:

$ app.wt --session-id-prefix=wt1 --http-port 9090 ...
$ app.wt --session-id-prefix=wt2 --http-port 9091 ...