Wt

h1. Using HAproxy as a reverse proxy

"HAproxy":http://haproxy.1wt.eu/ 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.

You need a fairly recent of haproxy for the options 'http-server-close' and 'http-pretend-keepalive' to work, which is needed for reliable load-balancing.

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

        option  http-server-close

        option  http-pretend-keepalive

        option  forwardfor

        option  originalto

        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. <a href="http://svtros.ru">!!!</a>

<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

        option  http-server-close

        option  http-pretend-keepalive

        option  forwardfor

        option  originalto

	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>

h2. Running multiple apps for multiple domains

In case you want different apps to be bound to different domains then I have the following configuration for you.

In my case it's a virtual Server for testing and development as well. With Apache to test wordpress and other things. 

To not immediately show changes on the Main Page I have a second instance running, but see for yourself:

I hope the comments are self explanatory even for beginners like I have been =)

<pre>

global

    maxconn 4096

    user     haproxy

    group    haproxy

    daemon

defaults

    log     global

    mode     http

    option    httplog

    option    dontlognull

    option    http-pretend-keepalive

    option    forwardfor

    option     originalto

    option     redispatch

    retries    3

    timeout    connect    5000

    timeout    client    50000

    timeout server     50000

frontend http-in

    bind *:80

# Having a .wt Application-Server for development/testing purposes with access regardless of path

#    but subdomain is dev: dev.sample.com / dev.example.com

#    While having several domains pointing to the same physical server

    acl is_dev_URL hdr_beg(host) -i dev.

# Main-Page to load when connecting to host: should load sample.com/wt1

    acl is_wt_Main   hdr_end(host) sample.com

# Secondary Page shown when connecting from 2nd URL: example.com/wt2

        acl is_wt_Second hdr_end(host) example.com

# Having apache for other reasons, too: testing wordpress / something

#     refers to specific path: html

        acl apache_path path_beg /html

# Following a folder architecture within docroot like:

#    docroot/wt1/[styles][images][whatever] 

#    docroot/wtSecondary/[styles][images] 

#       ->Just giving an example of having another folder name than deployment path

    acl wt_path     path_beg /wt1

    acl wt_path     path_beg /wt2

    acl wt_resource path_beg /resources

    acl wt_resource path_beg /wt1

    acl wt_resource path_beg /wtSecondary

# Checking whether Servers are up or down

    acl wt_srv_up nbsrv(wt_hp) gt 0

    acl wt_dev_up nbsrv(wt_dev) gt 0

# The Redirections:

#  Redirect to Location /wt1 if Main-Page,  no other app, Server is up, no apache path, no resource path, and no dev-server

    redirect location /wt1   if is_wt_Main  !wt_path      wt_srv_up     !apache_path    !wt_resource      !is_dev_URL

# Redirect Secondary

    redirect location /wt2   if is_wt_Second !wt_path wt_srv_up !apache_path !wt_resource !is_dev_URL

# Choose the Backend

    use_backend apache    if apache_path !wt_srv_up 

# HAProxy 1.5.x + :

    default_backend wt

# HAProxy 1.4.x - :

#    use_backend wt_live     if is_wt_Main is_wt_Second wt_path !is_dev_URL wt_srv_up

#     use_backend wt_dev    if is_dev_URL wt_dev_up

# The Backends

backend wt

# use-server is only available in HAProxy 1.5.x

        use-server Wt_Live unless is_dev_URL

    server Wt_Live  0.0.0.0:9050 track wt_hp/Wt_Live

    use-server Wt_Dev if is_dev_URL

    server Wt_Dev   0.0.0.0:9020 track wt_dev/Wt_Dev

backend wt_hp

    balance roundrobin  

    server Wt_Live 0.0.0.0:9050 check

backend apache

    balance roundrobin

    timeout connect 10s

    timeout server     30s

    server apache1 0.0.0.0:8050 check

backend wt_dev

    balance roundrobin

    server Wt_Dev 0.0.0.0:9020 check

</pre>

This is also updated to exclude deprecated keywords