Accumulators
This is an advanced topic. You should have already written a Custom Resource and be familiar with:
- The built-in Chef Infra
template
resource - Cookbook execution
with_run_context
Overview
An accumulator is a programming pattern that gathers multiple values together.
In the context of Custom Resources, the accumulator pattern collects a set of properties from Custom Resources, and then applies the collection to a resource.
The steps for setting up an accumulator pattern are:
- Declare a resource
- Edit the resource
- Add both resources to the :root
run_context
- Delay the actions on the resources
Example Accumulator: Samba
Samba Linux tool systems for supporting sharing resources in a network with Windows systems. Samba uses a single file for configuration. To share more than one directory using this configuration file, you need to write multiple samba_share
resources.
The accumulator pattern lets you split out each configuration section into its own resource.
samba_share 'first_share' do
comment 'exported share 1'
path '/srv/export'
guest_ok true
printable false
write_list ['test_user_1']
create_mask '0644'
directory_mask '0775'
options 'inherit permissions' => 'yes'
end
samba_share 'second_share' do
comment 'exported share 2'
path '/srv/export_2'
guest_ok false
printable false
write_list ['test_user_2']
create_mask '0644'
directory_mask '0775'
create_directory false
end
Example
The following example shows how to:
- Setup the template resource
- Set the
action
to:nothing
- Set the
delayed_action
to:create
. - Add the template resource to the
root
run context, which allows thesamba_share
resource to find it. - Use
edit_resource
to find the template - Use
edit_resource
to add new variables to the existing collection
Note: This uses the ||=
Ruby method to add a new Hash if one doesn’t exist already.
# action for the samba_server custom resource
action :create do
package 'samba'
# We need to force both the server template and the
# share templates into the root context to find each other
with_run_context :root do
template new_resource.config_file do
source 'smb.conf.erb'
owner 'root'
group 'root'
mode '0644'
cookbook 'samba'
variables(samba_options: new_resource.options)
action :nothing
delayed_action :create
end
end
end
# action for the samba_share custom resource
action :add do
with_run_context :root do
edit_resource(:template, new_resource.config_file) do |new_resource|
variables[:shares] ||= {}
variables[:shares][new_resource.share_name] ||= {}
variables[:shares][new_resource.share_name]['comment'] = new_resource.comment
variables[:shares][new_resource.share_name]['path'] = new_resource.path
end
end
end