Menu
AWS OpsWorks
User Guide (API Version 2013-02-18)

Attributes

Recipes and templates depend on a variety of values, such as configuration settings. Rather than hardcode such values directly in recipes or templates, you can create an attribute file with an attribute that represents each value. You then use the attributes in your recipes or templates instead of explicit values. The advantage of using attributes is that you can override their values without touching the cookbook. For this reason, you should always use attributes to define the following types of values:

  • Values that might vary from stack to stack or with time, such as user names.

    If you hardcode such values, you must change the recipe or template each time you need to change a value. By using attributes to define these values, you can use the same cookbooks for every stack and just override the appropriate attributes.

  • Sensitive values, such as passwords or secret keys.

    Putting explicit sensitive values in your cookbook can increase the risk of exposure. Instead, define attributes with dummy values and override them to set the actual values. The best way to override such attributes is with custom JSON. For more information, see Using Custom JSON.

For more information about attributes and how to override them, see Overriding Attributes.

The following example is a portion of an example attribute file.

Copy
... default["apache"]["listen_ports"] = [ '80','443' ] default["apache"]["contact"] = 'ops@example.com' default["apache"]["timeout"] = 120 default["apache"]["keepalive"] = 'Off' default["apache"]["keepaliverequests"] = 100 default["apache"]["keepalivetimeout"] = 3 default["apache"]["prefork"]["startservers"] = 16 default["apache"]["prefork"]["minspareservers"] = 16 default["apache"]["prefork"]["maxspareservers"] = 32 default["apache"]["prefork"]["serverlimit"] = 400 default["apache"]["prefork"]["maxclients"] = 400 default["apache"]["prefork"]["maxrequestsperchild"] = 10000 ...

AWS OpsWorks Stacks defines attributes by using the following syntax:

Copy
node.type["attribute"]["subattribute"]["..."]=value

You can also use colons (:), as follows:

Copy
node.type[:attribute][:subattribute][:...]=value

An attribute definition has the following components:

node.

The node. prefix is optional and usually omitted, as shown in the example.

type

The type governs whether the attribute can be overridden. AWS OpsWorks Stacks attributes typically use one of the following types:

  • default is the most commonly used type, because it allows the attribute to be overridden.

  • normal defines an attribute that overrides one of the standard AWS OpsWorks Stacks attribute values.

Note

Chef supports additional types, which aren't necessary for AWS OpsWorks Stacks but might be useful for your project. For more information, see About Attributes.

attribute name

The attribute name uses the standard Chef node syntax, [:attribute][:subattribute][...]. You can use any names you like for your attributes. However, as discussed in Overriding Attributes, custom cookbook attributes are merged into the instance's node object, along with the attributes from the stack configuration and deployment attributes, and Chef's Ohai tool. Commonly used configuration names such as port or user might appear in a variety of cookbooks.

To avoid name collisions, the convention is to create qualified attribute names with at least two elements, as shown in the example. The first element should be unique and is typically based on a product name like Apache. It is followed by one or more subattributes that identify the particular value, such as [:user] or [:port]. You can use as many subattributes as are appropriate for your project.

value

An attribute can be set to the following types of values:

  • A string, such as default[:apache][:keepalive] = 'Off'.

  • A number (without quotes) such as default[:apache][:timeout] = 120.

  • A Boolean value, which can be either true or false (no quotes).

  • A list of values, such as default[:apache][:listen_ports] = [ '80','443' ]

The attribute file is a Ruby application, so you can also use node syntax and logical operators to assign values based on other attributes. For more information about how to define attributes, see About Attributes s. For examples of working attribute files, see the AWS OpsWorks Stacks built-in cookbooks at https://github.com/aws/opsworks-cookbooks.

On this page: