collective.recipe.zopeinstancemultiplier 0.1.0

Overview

This recipe makes it easier to configure multiple Zope instances.

Example usage

We’ll start by creating a buildout that uses the recipe:

>>> write('buildout.cfg',
... """
... [buildout]
... parts = instance instance-multiplier
...
... [instance]
... recipe = collective.recipe.zopeinstancemultiplier:printer
... http-address = 8080
... option-foo = value-foo
... option-bar = value-bar
...
... [instance-multiplier]
... recipe = collective.recipe.zopeinstancemultiplier
... instance-part = instance
... count = 2
... """)

The instance-multiplier part is configured to generate two additional parts, using the instance part as a model. Two new parts will be created: instance-1 and instance-2. These parts will be exact clones of the model part, except for the http-address option, which will be incremented for each part. As a result we we’ll have:

• instance with http-address equals 8080.

• instance-1 with http-address equals 8081.

• instance-2 with http-address equals 8082.

The :printer recipe just prints out the part options at install time. We don’t want to generate real Zope instances just to test. In real life you would use plone.recipe.zope2instance.

Running the buildout gives us:

>>> print 'start', system(buildout)
start...
Installing instance.
http-address = 8080
option-bar = value-bar
option-foo = value-foo
Installing instance-1.
http-address = 8081
option-bar = value-bar
option-foo = value-foo
Installing instance-2.
http-address = 8082
option-bar = value-bar
option-foo = value-foo
...

Support for “ip:port” syntax

The “ip:port” syntax in the http-address option is also supported:

>>> write('buildout.cfg',
... """
... [buildout]
... parts = my-instance my-instance-multiplier
...
... [my-instance]
... recipe = collective.recipe.zopeinstancemultiplier:printer
... http-address = 127.0.0.1:1234
...
... [my-instance-multiplier]
... recipe = collective.recipe.zopeinstancemultiplier
... instance-part = my-instance
... count = 2
... """)

Running the buildout gives us:

>>> print 'start', system(buildout)
start...
Installing my-instance.
http-address = 127.0.0.1:1234
Installing my-instance-1.
http-address = 127.0.0.1:1235
Installing my-instance-2.
http-address = 127.0.0.1:1236
...

Adding a custom instance

Sometimes you want to have a custom instance in your cluster. To make configuration easier the “multiplier” part provides an special option containing the next port to be used. You can use this option like this:

>>> write('buildout.cfg',
... """
... [buildout]
... parts = instance instance-multiplier instance-custom
...
... [instance]
... recipe = collective.recipe.zopeinstancemultiplier:printer
... http-address = 8080
...
... [instance-multiplier]
... recipe = collective.recipe.zopeinstancemultiplier
... instance-part = instance
... count = 2
...
... [instance-custom]
... <= instance
... http-address = ${instance-multiplier:next-http-address}
... custom-option = custom-value
... """)

Running the buildout gives us:

>>> print 'start', system(buildout)
start ...
Installing instance.
http-address = 8080
Installing instance-1.
http-address = 8081
Installing instance-2.
http-address = 8082
...
Installing instance-custom.
custom-option = custom-value
http-address = 8083

Depending on the name of the part (${:_buildout_section_name} support)

Sometimes an option value must include the name of the part. Buildout supports this use case by providing the special value _buildout_section_name_.

The following example shows how this special value is used is commonly used in the multiple Zope instances scenario, without using this recipe:

[instance]
...
http-address = 8080
special-log-path = /path/to/the/logs/${:_buildout_section_name}.log

[instance-1]
<= instance
http-address = 8081

[instance-2]
<= instance
http-address = 8082

An attempt to adapt the previous example to work with this recipe would look like this:

[instance]
...
http-address = 8080
special-log-path = /path/to/the/logs/${:_buildout_section_name}.log

[instance-multiplier]
recipe = collective.recipe.zopeinstancemultiplier
instance-part = instance
count = 2

This, however, would fail. Because the way Buildout works, at the time the recipe has access to the instance part to multiply it, the variable substitution would already have occurred.

To make it work a simple adaptation is needed. Simply include an extra dollar sign in order to escape the variable. Here’s an example:

>>> write('buildout.cfg',
... """
... [buildout]
... parts = instance instance-multiplier
...
... [instance]
... recipe = collective.recipe.zopeinstancemultiplier:printer
... http-address = 8080
... special-log-path = /path/to/the/logs/$${:_buildout_section_name_}.log
...
... [instance-multiplier]
... recipe = collective.recipe.zopeinstancemultiplier
... instance-part = instance
... count = 2
... """)

Running the buildout gives us:

>>> print 'start', system(buildout)
start ...
Installing instance.
http-address = 8080
special-log-path = /path/to/the/logs/instance.log
Installing instance-1.
http-address = 8081
special-log-path = /path/to/the/logs/instance-1.log
Installing instance-2.
http-address = 8082
special-log-path = /path/to/the/logs/instance-2.log
...

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