Skip to content

Instantly share code, notes, and snippets.

@arangamani
Last active February 20, 2023 02:44
Show Gist options
  • Save arangamani/4659646 to your computer and use it in GitHub Desktop.
Save arangamani/4659646 to your computer and use it in GitHub Desktop.
Dynamically update attribute of a Chef resource during converge phase (Node variable assignment in Compile vs Converge)
# 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.
@dbaboy
Copy link

dbaboy commented Feb 20, 2023

@arangamani A question - if the file resource is moved to before ruby block the the content is not updated anymore! Is it possible to explain that.

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment