Grok-by-Example: Demosite

This post is part of a series of postings about more or less basic Grok apps that are ported from other python web frameworks. Motivation is that you can look at the original source and the grok code side-by-side and deduce from both. Source is available from svn.zope.org/grokapps/gbesite/.

This "site application" shows how to install multiple Grok applications and make them available from a single Grok instance (using ZEO and Apache). A test instance is available at gbe.d2m.at.

Review

Now that you have a few working Grok apps (Grok-By-Example), how about serving them all together from a single Grok instance?

One possible setup is to create the site as a Grok app on its own. You just construct the basic app layout (or let grokproject do it for you or simply checkout the 'gbesite' application). I strongly recommend to run your development from inside a virtualenv:

    $ svn co svn://svn.zope.org/repos/main/grokapps/gbesite
    $ cd gbesite
    $ virtualenv --no-site-packages .
    $ source bin/activate

    install_requires=[...
                      'gbeguestbook',
                      'gbe99bottles',
                      'gbewiki',
                      'gbepastebin',
                      ...
                     ],

Now checkout the packages from SVN to your 'gbesite' folder. If the packages where available from PyPI or another package repository you could just skip this and the next step, buildout would fetch and install the packages on the next run:

    svn co svn://svn.zope.org/repos/main/grokapps/gbeguestbook
    svn co svn://svn.zope.org/repos/main/grokapps/gbe99bottles
    svn co svn://svn.zope.org/repos/main/grokapps/gbewiki
    svn co svn://svn.zope.org/repos/main/grokapps/gbepastebin

In 'buildout.cfg' add the same packages to 'develop':

    [buildout]
    develop = . gbeguestbook gbe99bottles gbewiki gbepastebin

    $ bin/python bootstrap.py
    $ bin/buildout

You now want to setup all available example apps automatically when creating an instance of the site application. Adding an event subscription handler for the 'site' class does just that:

    @grok.subscribe(site, grok.IObjectAddedEvent)
    def handle(obj, event):
        applications=(('gbeguestbook.app.Application','Guestbook'),
                      ('gbe99bottles.app.Song','Song'),
                      ('gbewiki.app.WikiPage','Wiki'),
                      ('gbepastebin.app.Application','Pastebin'),
                      )
        for application, name in applications:
            app = zope.component.getUtility(grok.interfaces.IApplication,
                                            name=application)
            try:
                obj[name] = app()
            except DuplicationError:
                pass

The 'applications' list defines the example apps and their instance names. Whenever you create a new instance of your 'site' class the example apps will be created with their fixed names inside it.

If you want to serve your apps to the public, your site also should provide a 'robots.txt' file for the webcrawlers.

Add another grok.View to your application class and give it the name 'robots.txt':

    class Robots(grok.View):
        grok.name('robots.txt')

Then create another template file in 'app_templates/robots.pt'. The template could be empty or hold instructions following the robots exclusion standard.

Next create a virtual host to serve the site from behind Apache:

    <VirtualHost *>
    ServerName    your.server.name
    ...    
    RewriteEngine On
    RewriteRule ^/(.*)  http://127.0.0.1:8080/<site>/++vh++http:your.server.name:80/++/$1 [P,L]
    </VirtualHost>

(with <site> having the name of your public site instance). This should make your apps available at root level. Your 'app_templates/index.pt' template already holds links to all installed example apps and serves as default page for the Grok instance. If you need to access the 'admin' screens again point your browser to:

    http://localhost:8080/applications

Finally you want to debug the running site. Some of the example apps have no means to delete existing objects - but you can simply delete objects from the debugger too.

Debugging a running zope instance needs a change in the server setup: you create a ZEO server that holds the ZODB (Data.fs) and 2 ZEO clients that access their data from the ZEO server. One client ('zopectl') will serve the site application, the other client ('instance2') will be used for debugging.

You need to change 'buildout.cfg', add and modify parts:

    [buildout]
    ...
    parts = ... zodb server instance2
    [zodb]
    recipe = zc.recipe.egg:script
    eggs = ZODB3
    
    [server]
    recipe = zc.zodbrecipes:server
    zeo.conf =
       <zeo>
          address 8100
       </zeo>
       <filestorage 1>
          path ${buildout:parts-directory}/data/ZEOData.fs
       </filestorage>
    [zopectl]
    recipe = zc.zope3recipes:instance
    application = app
    address = 8080
    zope.conf = devmode on
        <zodb>
          <zeoclient>
            server 8100
          </zeoclient>
        </zodb>
        site-definition ${buildout:parts-directory}/app/site.zcml
        
        <accesslog>
          <logfile>
            path ${buildout:parts-directory}/zopectl/access.log
          </logfile>
        </accesslog>
        
        <eventlog>
          <logfile>
            formatter zope.exceptions.log.Formatter
            path STDOUT
          </logfile>
        </eventlog>
    
    [instance2]
    recipe = zc.zope3recipes:instance
    extends = zopectl
    address = 9080

Run buildout again, run the tests, start the server, start the client:

    $ bin/buildout
    $ bin/test
    $ bin/server start
    $ bin/zopectl fg

    $ sudo a2ensite your-vhost-id
    $ sudo /etc/init.d/apache2 restart

    http://your.server.name/applications