chef_attribute_converge.rb

# In Chef, when a resource is defined all its variables are evaluated during
# compile time and the execution of the resource takes place in converge phase.
# So if the value of a particular attribute is changed in converge
# (and not in compile) the resource will be executed with the old value.

# Example problem:
# Let's consider this situation where there are two steps involved in a recipe
# Step 1 is a Ruby block that changes a node attribute. Rubyblocks get executed
# in converge phase
# Step 2 is a Chef resource that makes use of the node attribute that was
# changed in Step 1

# ============= Without any modification to normal behavior ================= #

node[:test][:content] = "old content"

# Step 1
ruby_block "step1" do
  block do
    node[:test][:content] = "new content"
  end
end

# Step 2
file "/tmp/some_file" do
  owner "root"
  group "root"
  content node[:test][:content]
end

# =========================================================================== #
# file resource will still have the old content as it is set in the compile
# phase.

# ========================== With modified code ============================= #

node[:test][:content] = "old content"

# Step 1
ruby_block "step1" do
  block do
    node[:test][:content] = "new_content"

    # Dynamically set the file resource's attribute
    # Obtain the desired resource from resource_collection
    file_r = run_context.resource_collection.find(:file => "/tmp/some_file")
    # Update the content attribute
    file_r.content node[:test][:content]
  end
end

# Step 2
file "/tmp/some_file" do
  owner "root"
  group "root"
  content node[:test][:content]
end

# =========================================================================== #
# The file resource will now have the updated content.