Creating multiple instances with Buildout macros

As of version 1.4 of zc.buildout, it is possible to extend sections (except for the buildout section) with the use of the special < parameter. So, to create a macro, create a section with whatever you parameters you want in it, for example foo:

[foo]
bar = baz

Then create another section or sections such as foo1 and foo2 and set the < parameter with the value of the section you want to copy:

[foo1]
< = foo

[foo2]
< = foo

So foo1 and foo2 now contain:

bar = baz

You can now override and add whatever parameters you like:

[foo3]
< = foo
# bar gets bilge, instead of baz
bar = bilge
# car gets baz
car = ${foo:bar}

And so on.

That means we can now define a base instance section (which we did in buildout.cfg) and use it as a macro to create additional instance sections.

To demonstrate this, we will create two additional instances, based on the instance section in buildout.cfg.

In 06-deployment-optimization-macros.cfg, we have:

[buildout]
extends...