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Dynamically update attribute of a Chef resource during converge phase (Node variable assignment in Compile vs Converge)
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# 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. |
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@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.