Is it possible to detect the platform within the metadata.rb file of a Cookbook?
For example, something like this:
if node['platform'] == 'aix'
depends "cats", "< 1.0"
end
if node['platform'] == 'ubuntu'
depends "cats", "> 1.0"
end
But that is not possible since node is not available in that context. Is there any other way?
No, cookbook dependencies are entirely static. This has been discussed for some point in the future but no major proposals have emerged. If you are interested in contributing I would invite you to submit a Chef RFC with a proposed fix if you can come up with one :)
The sticky point is usually that there are reasons for conditional dependencies beyond simply per-platform logic. This comes up often for things like runit vs. systemd, mysql vs. postgres, and apache vs. nginx.