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

<pre>

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

</pre>

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.

<pre>

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

</pre>

And start the two Wt httpd servers using:

<pre>

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

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

</pre>