Masterbrain - A 'rev-proxy' like dispatcher.

tobbe — 2008-03-27T21:04:42+01:00

On my server at home I'm running a number of experimental systems
written in Erlang. Many of them have a web interface that I want
to expose to the Internet. Since I want them to be accessible as
subdomains of tornkvist.org, and on port 80; I have been using
lighttpd in front of them as a rev-proxy. This has been a bit
of annoyance since I have had to deal with the lighttpd's
configuration as well as my Yaws configuration for each system
of mine.

The Idea

This morning, on the way to work, I came up with a nice solution
that would make it possible to get rid of lighttpd and
in fact; also get rid of each Yaws server running on my systems.

The idea is very simple. On my server I will run one Erlang node
that runs Yaws. This is my web server. I configure Yaws to virt-host
my other systems, pointing the docroot accordingly for each of
the system. Then for each system I make sure that every .yaws file
only contains one single rpc-call to the actual system node. The
result from the rpc-call must be consumable by the Yaws server.

This means that none of my systems anylonger need to run Yaws of
their own. It also results in that no traditional rev-proxy work,
a la lighttpd, is needed. And as the final touch; it also makes
it possible to implement a simple form of load balancing.

So for example, my index.yaws of my eblog system now contains:

<erl>                                                                                                                                                                                                           
out(A) ->                                                                                                                                                                                                       
    mbrain:call(eblog, index, out, [A]).                                                                                                                                                                        
</erl>

The content that previously was located in index.yaws has now
moved into index.erl. The mbrain:call/4 function, which
executes in the Yaws server node, will check if there exist
any nodes that match eblog@HOST, and if so; it make an
rpc:call/4 to that node. If there are several node names that
match, one of them is picked by random. It is also possible to
specify a list of node names to mbrain:call/4 to cater for
the case where you want to load balance several nodes on the
same host.

Summary

So there you go; a simple rev-proxy like, load balancing,
front end dispatcher. The code can be found in my
git repos. You can
reach two of my systems that are located behind my
Masterbrain dispatcher; one is my
blog site and
the other is The Priority List
site.

Final remark

To only have a single function call in your .yaws file
is actually very good. It makes both debugging and hot
code replacement easier.

The dsl_engine demo

tobbe — 2008-05-07T14:47:53+02:00

I have been trying out Erlware recently; and I like it a lot!

As an example, I created a demo application that show the use of the dsl_engine I wrote about earlier. Now, before I explain in more detail how I did this with the Erlware tools; here is how to try it out:

wget http://faxien.googlecode.com/files/faxien-launcher-universal-0.3.3.py sudo python faxien-launcher-universal-0.3.3.py sudo /usr/local/erlware/bin/faxien install-release dslenginedemo /usr/local/erlware/bin/dslenginedemo

Point your browser to: http://localhost:9898/

blog.tornkvist.org

Masterbrain - A 'rev-proxy' like dispatcher.

The Idea

Summary

Final remark

The dsl_engine demo