NAME
AtomMQ - An atompub server that supports the message queue/bus model.
VERSION
version 1.0200
SYNOPSIS
use AtomMQ;
my $db_info = { dsn => 'dbi:SQLite:dbname=/path/to/foo.db' };
my $server = AtomMQ->new(db_info => $db_info);
$server->run;
DESCRIPTION
AtomMQ is an atompub server that supports the message queue/bus model.
Throughout this document, I will use the term message when referring to
an atom feed entry, since the point of this module is to use atompub for
messaging. The idea is that atom feeds correspond to conceptual queues
(or buses) and atom entries correspond to messages. AtomMQ extends
Inoue's Atompub::Server which extends Miyagawa's XML::Atom::Server. Can
you feel the love already?
To create an AtomMQ server, just copy the code from the "SYNOPSIS". Make
sure to change the dsn to something valid. You can run it via CGI or as
a mod_perl handler. To run in a FastCGI or PSGI environment, see the
"FastCGI" and "PSGI" sections in this document. This is highly
recommended because it will run considerably faster.
These examples assume that you have configured your web server to point
http requests starting with /atommq to the script you just created. To
publish a message, make a HTTP POST request:
$ curl -d ' allo
an important message
' http://localhost/atommq/feed=widgets
That adds a new message to a feed titled widgets. If that feed didn't
exist before, it will be created for you. To retrieve messages from the
widgets feed, make a HTTP GET request:
$ curl http://localhost/atommq/feed=widgets
That will get all the messages since the feed was created. Lets say you
are running a client that polls the feed and processes messages. If this
client dies, you will not want it to process all the messages again when
it comes back up. So clients are responsible for maintaining and
persisting the id of the last message they processed. This allows a
client to request only messages that came after the message with the
given id. They can do this by passing a Xlastid header:
$ curl -H 'Xlastid: urn:uuid:4018425e-f747-11df-b990-b7043ee4d39e' http://localhost/atommq/feed=widgets
METHODS
new
Arguments: \%db_info, $auto_create_db, $max_msgs_per_request
This is the AtomMQ constructor. Only $db_info is required. $db_info is a
hashref containing the database connection info as described in
"connect_info" in DBIx::Class::Storage::DBI. It must at least contain a
dsn entry. $auto_create_db defaults to 1. Set it to 0 if you don't want
AtomMQ to attempt to create the db tables for you. You can leave it set
to 1 even if the db tables already exist. Setting it to 0 improves
performance slightly. $max_msgs_per_request defaults to 100. This
default value may change in future versions, so you may want to set it
explicitly. It determines the maximum number of messages returned by the
server for a GET request. So if there were 1000 messages, a GET request
will return messages 1 - 100. To get messages 101 - 200, you should
provide the id of message 100 in the next GET request via the Xlastid
header, as shown above. See "DATABASE" for more info. Example:
my $server = AtomMQ->new(
auto_create_db => 0,
max_msgs_per_request => 100,
db_info => {
dsn => 'dbi:SQLite:dbname=/path/to/foo.db',
user => 'joe',
password => 'momma',
}
);
run
Arguments: None
Call this method to start the server.
DATABASE
AtomMQ uses a database to store its data. The db_info you pass to the
constructor must point to a database which you have write privileges to.
The tables will be created automagically for you if they don't already
exist. Of course for that to work, you will need create table
privileges. All databases supported by DBIx::Class are supported, which
are most major databases including postgresql, sqlite, mysql and oracle.
FastCGI
CGI can be very slow. Not to worry, AtomMQ can be run via FastCGI. This
requires that you have the FCGI module installed.
#!/usr/bin/perl
use AtomMQ;
use FCGI;
my $db_info = { dsn => "dbi:SQLite:dbname=/path/to/foo.db" };
my $request = FCGI::Request();
while($request->Accept() >= 0) {
my $server = AtomMQ->new(db_info => $db_info);
$server->run;
}
Here is an example lighttpd config. It assumes you named the above file
atommq.fcgi. Make sure you chmod +x atommq.fcgi.
fastcgi.server += (
"/atommq" => ((
"socket" => "/tmp/fcgi.sock",
"check-local" => "disable",
"bin-path" => "/path/to/atommq.fcgi",
)),
)
Now AtomMQ will be running via FastCGI under /atommq.
PSGI
AtomMQ can also be run in a PSGI environment via Plack. Here is one way
to do it. You will need to have Plack, CGI::Emulate::PSGI and
CGI::Compile installed for this example. Copy the following to
atommq.psgi.
use Plack::App::WrapCGI;
my $app = Plack::App::WrapCGI->new(script => "/path/to/atommq.cgi")->to_app;
The "/path/to/atommq.cgi" string should be changed to the path to a cgi
script such as the one in the "SYNOPSIS". Then you can for example run:
plackup -p 5000 atommq.psgi
Now AtomMQ is running on port 5000 via the HTTP::Server::PSGI web
server. Of course you can use any PSGI/Plack web server via the -s
option to plackup.
MOTIVATION
I like messaging systems because they make it so easy to create scalable
applications. Existing message brokers are great for creating message
queues. But once a consumer reads a message off of a queue, it is gone.
I needed a system to publish events such that multiple heterogeneous
services could subscribe to them. So I really needed a message bus, not
a message queue. I could for example have used something called topics
in ActiveMQ, but I have found them to have issues with persistence.
Actually, I have found ActiveMQ to be broken in general. An instance I
manage has to be restarted at least twice a week. AtomMQ on the other
hand will be extremely stable, because it is so simple. It is in essence
just an interface to a database. As long as your database and web server
are up, AtomMQ will be there for you. She will not let you down. And
there are all sorts of ways to add redundancy to databases and web
heads. Another advantage of using AtomMQ is that atompub is an RFC
standard. Everyone already has a client for it, their browser. Aren't
standards great! By the way, if you just need message queues, try
POE::Component::MessageQueue. It rocks. If you need a message bus, give
AtomMQ a shot.
AUTHOR
Naveed Massjouni
COPYRIGHT AND LICENSE
This software is copyright (c) 2010 by Naveed Massjouni.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.