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Tranforming Varnish backends for HAProxy

Let's say you want to transform a varnish:backends value to what can be used inside haproxy:

>>> write('buildout.cfg',
... """
... [buildout]
... parts = scripty echobackends echorepeat
...
... [varnish]
... backends =
...     myhost.com:255.255.255.1
...     myhost2.com:125.125.125.1
...
... [scripty]
... recipe = mr.scripty
... backends =
...   ... res = ""
...   ... for line in self.buildout['varnish']['backends'].splitlines():
...   ...    if ':' not in line:
...   ...      continue
...   ...    host, dest = line.strip().split(':')
...   ...    host = host.split('.')[0]
...   ...    res += "acl {} url_sub VirtualHostRoot/{}\\n".format(host, dest)
...   ... return res
... repeat =
...   ... opt_repeatx = int('10')
...   ... fun_repeatx = self.repeatx()
...   ... return '\\n'.join(["this is line %s"%i for i in range(1,opt_repeatx+1)])
... repeatx = return '10'
...
... [echobackends]
... recipe = mr.scripty
... install = print(self.buildout['scripty']['backends']); return []
...
... [echorepeat]
... recipe = mr.scripty
... install =
...   ... script = self.buildout['scripty']
...   ... print(script['repeat'])
...   ... return []
... """)

Running the buildout gives us:

>>> print(system(buildout))
Installing scripty.
Installing echobackends.
acl myhost url_sub VirtualHostRoot/255.255.255.1
acl myhost2 url_sub VirtualHostRoot/125.125.125.1
Installing echorepeat.
this is line 1
this is line 2
this is line 3
this is line 4
this is line 5
this is line 6
this is line 7
this is line 8
this is line 9
this is line 10...

From this example you'll notice several things. Options that are part of a mr.scripty part are turned into methods of the part instance and can call each other. In addition, each method can be called from other buildout recipes by accessing the option via ${part:method} or in code via self.buildout[part][method].

Offsetting port numbers

The following example will make all the values of ports_base available with an offset added to each one. This example demonstrates the special init option, which enables you to run a special function where the result is not stored against the part within buildout:

[ports_base]
instance1=8101
instance2=8102

[ports]
recipe = mr.scripty
OFFSET = 1000
init =
    ... for key,value in self.buildout['ports_base'].items():
    ...     self.options[key] = str(int(value)+int(self.OFFSET))

So, the usage of init enables us to create options against the [ports] section using arbitrary code. In the example above, this will result in all of the options under [ports_base] being processed to add the OFFSET value to the port. The end result is that other sections of buildout can now reference ${ports:instance1} and ${ports:instance2}, which will have values of 9101 and 9102 respectively.

Different download links for certain architectures

This example usage shows how to alter download links for third-party libraries based upon whether the host platform is 32 or 64-bit. Note that the example uses Python 2.6 or later:

[buildout]
parts =
    ...
    download

[scripty]
recipe = mr.scripty
DOWNLOAD_URL_64 = http://site.com/64bit.tgz
DOWNLOAD_URL_32 = http://site.com/32bit.tgz
download_url =
    ... import platform
    ... is_64bit = any(['64' in x for x in platform.architecture()])
    ... return is_64bit and self.DOWNLOAD_URL_64 or self.DOWNLOAD_URL_32

[download]
recipe = hexagonit.recipe.download
url = ${scripty:download_url}

Checking existence of directories

This example tests the existence of a list of directories and selects the first one that can be found on the system. In this particular example, we look through a list of potential JDK directories, as the location will differ across Linux distributions, in order to install an egg that depends on having a Java SDK install available:

[buildout]
parts =
    ...
    jpype

[scripty]
recipe = mr.scripty
JAVA_PATHS =
    /usr/lib/jvm/java-6-openjdk
    /etc/alternatives/java_sdk
    ${buildout:directory}
java =
    ... import os
    ... paths = self.JAVA_PATHS.split('\n')
    ... exists = [os.path.exists(path) for path in paths]
    ... return paths[exists.index(True)]

[java-env]
JAVA_HOME = ${scripty:java}

[jpype]
recipe = zc.recipe.egg:custom
egg = JPype
find-links =
    http://aarnet.dl.sourceforge.net/project/jpype/JPype/0.5.4/JPype-0.5.4.1.zip
environment = java-env