on_failure cookbook

This cookbook is a proof of concept for the proposed on_failure Chef RFC. This cookbook doesn't implement all possible features proposed but it covers most use cases for the feature. There are still discussions going on in the proposal on how do certain things. This cookbook will help playing with the feature and proposing changes to the RFC.

Follow this blog post for seeing this in action.

Requirements

• Requires Chef 11.
• Willingness to take risk (as it is still a brand new concept).

Usage

Add the following depends statement to your metadata.rb.

depends 'on_failure'

Once this cookbook is loaded, you will have access to the on_failure construct in any resource.

Simple Example

meal 'breakfast' do
  on_failure { notify :eat, 'food[bacon]' }
end

If the meal[breakfast] resource's :eat action fails, it will notify the :eat action of 'food[bacon]' resource and then retry the :eat action again.

Handling specific exceptions

A specific exception can be specified in the on_failure construct which will catch only the matching exceptions. For example:

meal 'breakfast' do
  on_failure(HungryError) { notify :eat, 'food[bacon]' }
end

In this example, we only want to catch the HungryError exception. All other exceptions will immediately raise.

Specifying retries

By default the action will be retried only once. But you can specify the number of times the action should be retried.

meal 'breakfast' do
  on_failure(retries: 5) { notify :eat, 'food[bacon]' }
end

In this example, the action will be retried 5 times before the exception is raised. If the action succeeds before all retries, we are good and nothing wil be raised.

Specifying multiple exceptions

Multiple exceptions classes can be specified to be caught. You can also include the options such as retries along with specifying exceptions.

meal 'breakfast' do
  on_failure(UncookedError, HungryError, retries: 3) { notify :fry, 'food[bacon]' }
end

Specifying multiple blocks

If each exception should be handled differently, you can specify them in separate on_failure blocks. They will be executed in the order they are defined (top-bottom).

meal 'breakfast' do
  on_failure(UncookedError) { notify :fry, 'food[bacon]' }
  on_failure(ColdError) { notify :microwave, 'food[bacon]' }
end

Access to resource attributes

The attributes of the resource can be accessed inside the block of on_failure. The following example demonstrates feature.

meal 'breakfast' do
  time '2014-04-09 08:00:00 -0700'
  on_failure { |breakfast| Chef::Log.info "Tried eating breakfast at: #{breakfast.time}" }
end

This handler simply logs the time specified in the resource.

Testing/Playing

There are three cookbooks available in the test/cookbooks directory that will help playing with this resource.

Cookbooks

• sample - A sample cookbook that uses the on_failure feature to demonstrate how it works.
• meal - The cookbook that provides the meal resource.
• food - The cookbook that provides the food resource.

This cookbook has a Vagrantfile that can be used to provision a virtual machine and start playing with stuffs.

The sample cookbook has recipes for each use cases explained in the Usage section. Just pick any recipe, put it in the runlist of the virtualmachine and provision it to see it in action.

Attributes

There are no attributes in this cookbook.

Recipes

There are no recipes in this cookbook.

License & Author

Author:: Kannan Manickam (me@arangamani.net)

Copyright (C) 2014 Kannan Manickam

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.