Chef Resource Cache

This cookbook provides a resource_cache LWRP. Its purpose is to save time for cookbook authors. It can cache expensive and time-consuming resource invocations between chef runs.

Resource caching is disabled by default. The goal is to make the LWRP easy and safe to use for cookbook authors without surprising end-users.

Requirements

None -- just Chef.

Version

0.5

Usage

###Quick Start

• Wrap resources in resource_cache blocks
• Set resource_cache['enable'] = true
• Set resource_cache['ttl'] = <minutes>
• Cookbook authors: please do NOT set these attributes as part of a library cookbook you distribute. Instead, set them locally for your development cycle.

###Simple caching: # Cache until TTL expiration resource_cache do resources do execute 'apt-get update' end end

###Conditional caching: # Cache until TTL expiration or conditions change resource_cache do conditions ({ :prefix => '/opt/software', :version => '1.0' }) resources do bash 'compile software' do # Expensive compilation... end bash 'install software' do # Expensive copying/installing end end end

Note conditions ({}) above. Using conditions {} would be interpreted as a block instead of a hash.

How It Works

The LWRP serializes state to json files under chef's cache directory. It stores a timestamp and the cache conditions (if specified) when a wrapped resource is updated. On subsequent chef runs, the serialized state is loaded. If the current cache conditions match the prior cache conditions and the updated timestamp is within the TTL, the wrapped resources are skipped.

Cache Invalidation

Any of the following will disable cache entries:

• Setting bypass true for a cache entry
• Changing the conditions ({}) for a cache entry
• Setting the resource_cache.ttl attribute to 0
• Setting the resource_cache.enable attribute to false
• Removing the cache files from the resource_cache.dir directory

Attributes

Key	Type	Description	Default
['resource_cache']['enable']	Boolean	whether to enable the cache	false
['resource_cache']['ttl']	Integer	Time-to-live (expiration) in minutes	0
['resource_cache']['dir']	String (path)	Directory to store cache files	Chef::Config[:file_cache_path]/resource_cache, or [SYSTEM TMP]/resource_cache if :file_cache_path is unset

Gotchas

If you use vagrant for Chef development (highly recommended), watch out for conflict with vagrant cache plugins. Some of these may store /var/chef/cache outside of the VM, on the host filesystem. If the contents of this directory are retained after a VM is destroyed, the resource_cache might produce false cache hits. The solution is to set the resource_cache.dir attribute to a directory that is kept within the VM (e.g. /var/chef-resource-cache).

Development TODO

1. Write tests. Yes, I'm a horrible person for releasing this without tests...
2. Normalize cache file names by stripping/replacing characters that aren't shell friendly.

Contributing

1. Fork the repository on Github
2. Create a named feature branch (like add_tests -- wink wink)
3. Write your change
4. Submit a Pull Request using Github

License and Authors

Copyright 2013, Bob Ziuchkovski bob@bz-technology.com

Copyright 2013, UserTesting.com

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