{"id":674,"date":"2022-11-24T03:21:59","date_gmt":"2022-11-24T03:21:59","guid":{"rendered":"http:\/\/www.scmgalaxy.com\/tutorials\/2017\/07\/26\/chef-notifies-and-subscribes-explained-with-examples\/"},"modified":"2022-12-23T05:45:27","modified_gmt":"2022-12-23T05:45:27","slug":"chef-notifies-and-subscribes-explained-with-examples","status":"publish","type":"post","link":"https:\/\/www.devopsschool.com\/blog\/chef-notifies-and-subscribes-explained-with-examples\/","title":{"rendered":"Chef Tutorials – notifies and subscribes explained with examples of Notifications"},"content":{"rendered":"

Chef notifies and subscribes explained with examples<\/h3>\n
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A notification is a property on a resource that listens to other resources in the resource collection and then takes actions based on the notification type (notifies or subscribes).<\/div>\n
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Timers<\/h3>\n
A timer specifies the point during the chef-client run at which a notification is run. The following timers are available:<\/div>\n
:before<\/strong><\/div>\n
Specifies that the action on a notified resource should be run before processing the resource block in which the notification is located.<\/div>\n
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:delayed<\/strong><\/div>\n
Default. Specifies that a notification should be queued up, and then executed at the very end of the chef-client run.<\/div>\n
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:immediate, :immediately<\/strong><\/div>\n
Specifies that a notification should be run immediately, per resource notified.<\/div>\n
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Notifies<\/h3>\n
A resource may notify another resource to take action when its state changes. Specify a ‘resource[name]’, the :action that resource should take, and then the :timer for that action. A resource may notify more than one resource; use a notifies statement for each resource to be notified.<\/div>\n
The syntax for notifies is:<\/div>\n
notifies :action, ‘resource[name]’, :timer<\/div>\n
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Example<\/strong><\/div>\n
The following examples show how to use the notifies notification in a recipe.<\/div>\n
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Delay notifications<\/strong><\/div>\n
template ‘\/etc\/nagios3\/configures-nagios.conf’ do<\/div>\n
\u00a0 # other parameters<\/div>\n
\u00a0 notifies :run, ‘execute[test-nagios-config]’, :delayed<\/div>\n
end<\/div>\n
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Notify immediately<\/strong><\/div>\n
By default, notifications are :delayed, that is they are queued up as they are triggered, and then executed at the very end of a chef-client run. To run an action immediately, use :immediately:<\/div>\n
template ‘\/etc\/nagios3\/configures-nagios.conf’ do<\/div>\n
\u00a0 # other parameters<\/div>\n
\u00a0 notifies :run, ‘execute[test-nagios-config]’, :immediately<\/div>\n
end<\/div>\n
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and then the chef-client would immediately run the following:<\/div>\n
execute ‘test-nagios-config’ do<\/div>\n
\u00a0 command ‘nagios3 –verify-config’<\/div>\n
\u00a0 action :nothing<\/div>\n
end<\/div>\n
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Subscribes<\/h3>\n
A resource may listen to another resource, and then take action if the state of the resource being listened to changes. Specify a ‘resource[name]’, the :action to be taken, and then the :timer for that action.<\/div>\n
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Note that subscribes does not apply the specified action to the resource that it listens to – for example:<\/div>\n
file ‘\/etc\/nginx\/ssl\/example.crt’ do<\/div>\n
\u00a0 \u00a0mode ‘0600’<\/div>\n
\u00a0 \u00a0owner ‘root’<\/div>\n
end<\/div>\n
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service ‘nginx’ do<\/div>\n
\u00a0 \u00a0subscribes :reload, ‘file[\/etc\/nginx\/ssl\/example.crt]’, :immediately<\/div>\n
end<\/div>\n
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In this case the subscribes property reloads the nginx service whenever its certificate file, located under \/etc\/nginx\/ssl\/example.crt, is updated. subscribes does not make any changes to the certificate file itself, it merely listens for a change to the file, and executes the :reload action for its resource (in this example nginx) when a change is detected.<\/div>\n
The syntax for subscribes is:<\/div>\n
subscribes :action, ‘resource[name]’, :timer<\/div>\n
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Examples<\/strong><\/div>\n
The following examples show how to use the subscribes notification in a recipe.<\/div>\n
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Prevent restart and reconfigure if configuration is broken<\/div>\n
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Use the :nothing action (common to all resources) to prevent the test from starting automatically, and then use the subscribes notification to run a configuration test when a change to the template is detected:<\/div>\n
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execute ‘test-nagios-config’ do<\/div>\n
\u00a0 command ‘nagios3 –verify-config’<\/div>\n
\u00a0 action :nothing<\/div>\n
\u00a0 subscribes :run, ‘template[\/etc\/nagios3\/configures-nagios.conf]’, :immediately<\/div>\n
end<\/div>\n
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Reference<\/strong><\/div>\n
https:\/\/docs.chef.io\/resources.html#id4<\/a><\/div>\n
https:\/\/docs.chef.io\/resource_common\/#notifications<\/div>\n
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Example<\/strong><\/div>\n
https:\/\/gist.github.com\/nathanhoel\/f5433a0d9cfe2e717c71<\/a><\/div>\n\n