Chef has different execution phases. Especially the compile and converge phase are important when writing cookbooks: the resources are collected in the compile phase and are executed in the converge phase.
In some special cases you might want to have dynamic resources, which are created and executed in the converge phase. The main background is that you want to react on something you known in the execution phase only.
Given a situation where you want to cleanup configuration files, which get installed by some package during a chef run (real examples might be apache on debian or freeradius on RHEL). You can try to solve this situation like this:
package 'freeradius' # Our module configuration template '/etc/raddb/mods-available/eap-tls' do ... end Dir.glob('/etc/raddb/mods-available/*').each do |mod_path| file_name = File.basename(mod_path) next if file_name == 'eap-tls' file mod_path do action :delete end end
However this will not work: you try to glob over
/etc/raddb/mods-available in the compile phase, but this path doesn’t exist as freeradius gets installed in the converge phase.
You can execute the package installation in the compile phase:
Still if this works, this way has one disadvantage: usually if your recipe can not be compiled due to some error, you will get an exception during the compile phase without to have any changes on our system (as execution phase isn’t invoked). By invoking the
run_action the resource will be executed immediately: the package get installed but you might have a compile error somewhere later. This is probably not what you usually expect.
Another possible way is to use dynamic resources: to create and to execute resources during the execution phase:
package 'freeradius' # Our module configuration template '/etc/raddb/mods-available/eap-tls' do ... end ruby_block 'cleanup the configs' do block do Dir.glob('/etc/raddb/mods-available/*').each do |mod_path| file_name = File.basename(mod_path) next if file_name == 'eap-tls' run_context.resource_collection << delete_path = Chef::Resource::File.new(mod_path, run_context) delete_path.action :delete end end end
ruby_block’s block gets executed in the converge phase and after the package is installed. However you can’t use Chef DSL in the ruby_block (as its not evaluated in the context of
Chef::Recipe). You have to create the resources in Ruby and add them to the resource collection of current run context of Chef. See rubydoc for more documentation on resources.