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https://github.com/poise/poise-appenv

Helpers for application-specific envronment settings in Chef
https://github.com/poise/poise-appenv

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Helpers for application-specific envronment settings in Chef

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poise-appenv

=============



[![Build Status](https://travis-ci.org/poise/poise-appenv.png?branch=master)](https://travis-ci.org/poise/poise-appenv)



Quick Start

-----------



### Attributes



In your [default attributes file](test/cookbooks/poise-appenv_test/attributes/default.rb#L19)

configure the name of the cookbook that determines your application environment:



```ruby

default['poise-appenv']['cookbook'] = 'role-myapp'

```



Then create one attribute file for each [app_environment](test/cookbooks/poise-appenv_test/attributes/prod.rb#L19-L20)

with a header like:



```ruby

include_attribute 'role-myapp'

return unless node.app_environment?('prod')

```



This header will prevent executing the file unless the app_environment

matches the given name(s). Put any shared attributes on the `default.rb` file

and per-app_environment attribute in the relevant file.



### Recipes



The cookbook specified in `node['poise-appenv']['cookbook']` is used to determine

which app_environment we are in. Each recipe within the cookbook maps to an

app_environment of that name, so adding `role-myapp::prod` to the run list

will mark the node as being in the `prod` app_environment. If you add plain

`role-myapp` to the run list, it will use the name of the chef_environment.



To accomplish this you need to create stub recipes like [recipes/prod.rb](test/cookbooks/poise-appenv_test/recipes/prod.rb)

which just include the default recipe:



```ruby

include_recipe 'role-myapp'

```



The default recipe should contain the normal code for installing your application,

generally this will be one more `include_recipe` to other cookbooks.



Application Environments

------------------------



Application environments offer a way to have different node attributes applied

via a cookbook. Combined with [role or environment cookbooks](http://vialstudios.logdown.com/posts/166848-the-environment-cookbook-pattern)

this lets you separate the varying configuration of an application in different

deployment scenarios from the code to install the application.



As a concrete example, imagine you have two Chef environments; prod and test.

You run a cluster of servers in each environment with your application installed.

Now you want to launch a new cluster in your test environment running an

experimental build and divert some portion of traffic to it. You could create

a new Chef environment by copying the existing test one, but almost all the

settings will be the same, only the version to deploy and similar attributes

need to be overridden for the new servers. Application environments give you

a way to apply those customizations.



Reference

---------



### `node.app_environment(cookbook=nil)`



`node.app_environment` returns the name of the detected application environment

based on the given or configured cookbook. Note that this is a method, not a

node attribute.



### `node.app_environment?(*names)`



`node.app_environment?` returns true if the current application environment

is any of the given names.



### `node['poise-appenv']['cookbook']`



`node['poise-appenv']['cookbook']` is a node attribute used to configure which

cookbook is searched for to determine the current application environment.



Why?

----



Why not just use Chef environments? Sometimes you want to deploy slightly

different applications in the same Chef environment. An example would be

launching a new branch of your code in the test environment. You could copy the

Chef environment and tweak the settings you want, but this results in a lot of

duplicated configuration which is error prone and difficult to update.

Additionally, even though it is slightly different, this hypothetical new

application cluster is still semantically in the "test" environment, and

currently Chef environments don't have any kind of heirarchical relationship.