=============================
gocept Link Monitoring Server
=============================

The Link Monitoring Server (lms) is a coherent set of components to regularly
check that URLs area reachable. It currently supports http, https and ftp URLs.


History
=======

gocept.lms is the third version of lms (hence the initial version of 3.x).

The first version was directly integrated into CMFLinkChecker and ran as a
thread.  This was not very stable.

The second version was using the Twisted framework and used a MySQL as a
backend. This was not very stable either.

The third version now is written in Zope 3 / Grok, uses the ZODB as data
storage and separates concerns where ever possible. This is stable.


Building blocks
===============

The lms consists of little blocks which only communicate via storing data in
the ZODB.

XML-RPC server
++++++++++++++

The XML-RPC server is the API to talk to the lms. It provides functions to
register and deregister clients and urls.  A management system can register
clients. A client can register URLs it wants to be checked by the lms.

Scheduler
+++++++++

The scheduler looks over the URLs that where added by the clients. It decides
which URLs have to be checked and puts them into the check queue.


Checker
+++++++

The checker pulls URLs from the check queue and checks them. It checks up to 20
URLs at the same time, but only once per second per host to avoid overload.

Notifier
++++++++

The notifier keeps the registered clients updated about the state information
for the URLs they subscribed to. Clients are notified via XML-RPC.

Synchroniser / Syncer
++++++++++++++++++++++

The syncer is responsible to keep the URL databases of the lms and the clients
synchronized. It does this daily by getting a full snapshot of the clients'
databases and provides them with the current status information for all URLs
they are interested in.

Installation
============

The installation works with a buildout. An example can be found at our SVN::

    % svn co http://svn.gocept.com/repos/gocept/gocept.lms/deployment/profiles

The buildout currently defines two profiles:

- prod.cfg for a production setup
- test.cfg for a test setup

The profiles are not really different right now, though. They're there to
illustrate the possibilities. The test profile looks like this::

    [buildout]
    extends = base.cfg

    [app]
    admin-password = admin
    appname = test    
    mail-server-host = localhost

    [zeo]
    address = localhost:8100

    [lms]
    address = localhost:8080


To select the test profile create a buildout.cfg which includes it::

    [buildout]
    extends = profiles/test.cfg

Next, bootstrap the buildout with python 2.5::

    % python2.5 bootstrap.py

This creates the actual buildout script as ``bin/buildout``::

    % bin/buildout

After the buildout was run there are scripts created to start the various
parts. The test profile uses a deployment sandbox, so all the scripts are
contained in ``parts/deployment/etc/init.d``::


To get started, first start the ZEO and the lms web interface::

    % parts/deployment/etc/init.d/lms-zeo start
    % parts/deployment/etc/init.d/lms-web start

Point your browser to http://localhost:8080. this opens the grok admin UI.
Create a lms with the id ``test``. Once created the lms will display
"Congratulations". 


Start the other services now::

    % parts/deployment/etc/init.d/lms-checker start
    % parts/deployment/etc/init.d/lms-notifier start
    % parts/deployment/etc/init.d/lms-scheduler start
    % parts/deployment/etc/init.d/lms-syncer start


The next step is to register a client. The lms welcome page has a link to a
very rudimentary form. There you have to enter:

Client Id
    This is an identificator for the client. It is used to authenticate.

Password
    The password to authenticate the client.

Contact name
    Emails sent by the lms will contain the name to address the recipient.

Contact email address	
    Emails sent by the lms regarding this client will be sent to this address.

Callback URL	
    The callback url is the XML-RPC point where the callback methods are
    called. For a gocept.linkchecker installation this would be
    http://example.com/portal_linkchecker/database/.

After registring the client you can configure gocept.linkchecker (or any other
client) to talk to the lms.
