Chef Custom Resources : mutable property or an alternative - ruby

Question

I read that as of 2016 OpsCode recommends against LWRP and the alternative HWRP. They rather recommend to use custom resources.
While this makes sense it leaves a lot to be desired in terms of leveraging ruby (unless I've misunderstood?)
I would like to be able to modify an array based on some boolean properties. I can then use that array to pass to the template, as in:
property :get_iptables_info, [TrueClass, FalseClass], default: false
property :get_pkglist, [TrueClass, FalseClass], default: false
property :cw_logs, Array, default: [], required: false
action :create do
ruby_block 'cw_iptables' do
block do
new_resource.cw_logs.push({ "#{new_resource.custom_dir}/iptables/iptables.txt" => { "log_group_name" => new_resource.log_group_name+"/iptables"}})
end
action :run
only_if {new_resource.get_iptables_info}
end
template "my_template" do
variables ({:logstreams => cw_logs})
end
end
Then in my template:
<% #logstreams.each_pair do |path, _object| %>
["#{path}"]
log_group_name = _object["log_group_name"]
<% end %>
The problem is that properties are immutable. So I get the error:
RuntimeError
------------
ruby_block[cw_iptables] (/tmp/kitchen/cache/cookbooks/custom_cw/resources/logs.rb line 43) had an error: RuntimeError: can't modify frozen Array
What's the correct way to do this? What's the correct way to write ruby code within the resource so that it's more modular and uses methods/functions?

Answer 1

Mutating properties inside a custom resource is generally a bad idea (there are exceptions but this isn't one of them). Better would be to use a local variable. Related, you don't need to use a ruby_block like that when you're already in a custom resource's action:
action :create do
cw_logs = new_resource.cw_logs
if new_resource.get_iptables_info
cw_logs += [whatever extra stuff you want]
end
template "my_template" do
variables logstreams: cw_logs
end
end
Notably that's using += instead of push which doesn't mutate the original. If you used push you would want cw_logs = new_resource.cw_logs.dup or similar.