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

Overriding Built-In Templates

Note

This topic applies only to Linux stacks. You cannot override built-in templates on Windows stacks.

The AWS OpsWorks Stacks built-in recipes use templates to create files on instances, primarily configuration files for servers, such as Apache. For example, the apache2 recipes use the apache2.conf.erb template to create the Apache server's primary configuration file, httpd.conf (Amazon Linux) or apache2.conf (Ubuntu).

Most of the configuration settings in these templates are represented by attributes, so the preferred way to customize a configuration file is by overriding the appropriate built-in attributes. For an example, see Overriding Built-In Attributes. However, if the settings that you want to customize aren't represented by built-in attributes, or aren't in the template at all, you must override the template itself. This topic describes how to override a built-in template to specify a custom Apache configuration setting.

You can provide custom error responses to Apache by adding ErrorDocument settings to the httpd.conf file. apache2.conf.erb contains only some commented-out examples, as shown in the following:

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... # # Customizable error responses come in three flavors: # 1) plain text 2) local redirects 3) external redirects # # Some examples: #ErrorDocument 500 "The server made a boo boo." #ErrorDocument 404 /missing.html #ErrorDocument 404 "/cgi-bin/missing_handler.pl" #ErrorDocument 402 http://www.example.com/subscription_info.html ...

Because these settings are hardcoded comments, you can't specify custom values by overriding attributes; you must override the template itself. However, unlike with attributes, there is no way to override particular parts of a template file. You must create a custom cookbook with the same name as the built-in version, copy the template file to the same subdirectory, and modify the file as needed. This topic shows how to override apache2.conf.erb to provide a custom response to error 500. For a general discussion of overriding templates, see Using Custom Templates.

Important

When you override a buiIt-in template, the built-in recipes use your customized version of the template instead of the built-in version. If AWS OpsWorks Stacks updates the built-in template, the custom template becomes out of sync and might not work correctly. AWS OpsWorks Stacks doesn't make such changes often, and when a template does change, AWS OpsWorks Stacks lists the changes and gives you the option of upgrading to a new version. We recommend that you monitor the AWS OpsWorks Stacks repository for changes, and manually update your custom template as needed. Note that the repository has a separate branch for each supported Chef version, so be sure that you are in the correct branch.

To start, create a custom cookbook.

To create the cookbook

  1. In the opsworks_cookbooks directory, create a cookbook directory named apache2, and then navigate to it. To override built-in templates, the custom cookbook must have the same name as the built-in cookbook, apache2 for this example.

    Note

    If you have already completed the Overriding Built-In Attributes walkthrough, you can use the same apache2 cookbook for this example, and skip Step 2.

  2. Create a metadata.rb file with the following content, and then save it to the apache2 directory.

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    name "apache2" version "0.1.0"
  3. In apache2 directory, create a templates/default directory..

    Note

    The templates/default directory works for Amazon Linux and Ubuntu 12.04 instances, which use the default apache2.conf.erb template. Ubuntu 14.04 instances use an operating system-specific apache2.conf.erb template, which is in the templates/ubuntu-14.04 directory. If you want the customization to apply to Ubuntu 14.04 instances also, you must override that template too.

  4. Copy the built-in apache2.conf.erb template to your templates/default directory. Open the template file, uncomment the ErrorDocument 500 line, and provide a custom error message, as follows:

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    ... ErrorDocument 500 "A custom error message." #ErrorDocument 404 /missing.html ...
  5. Create a .zip archive of opsworks_cookbooks named opsworks_cookbooks.zip, and then upload the file to an Amazon Simple Storage Service (Amazon S3) bucket. For simplicity, make the archive public. Record the archive's URL for later use. You can also store your cookbooks in a private Amazon S3 archive or in other repository types. For more information, see Cookbook Repositories.

Note

For simplicity, this example adds a hardcoded error message to the template. To change it, you must modify the template and reinstall the cookbook. To give yourself greater flexibility, you can define a default custom attribute for the error string in the custom cookbook's customize.rb attribute file and assign the value of that attribute to ErrorDocument 500. For example, if you name the attribute [:apache][:custom][:error500], the corresponding line in apache2.conf.erb would then look something like the following:

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... ErrorDocument 500 <%= node[:apache][:custom][:error500] %> #ErrorDocument 404 /missing.html ...

You can then change the custom error message at any time by overriding [:apache][:custom][:error500]. If you use custom JSON to override the attribute, you don't even need to touch the cookbook.

To use the custom template, create a stack and install the cookbook.

To use the custom template

  1. Open the AWS OpsWorks Stacks console, and then choose Add Stack.

  2. Specify the following standard settings:

    • Name – ApacheTemplate

    • Region – US West (Oregon)

    • Default SSH key – An Amazon Elastic Compute Cloud (Amazon EC2) key pair

      If you need to create an Amazon EC2 key pair, see Amazon EC2 Key Pairs. Note that the key pair must belong to the same AWS region as the instance.

    Choose Advanced>>, choose Use custom Chef cookbooks, to specify the following settings:

    • Repository typeHttp Archive

    • Repository URL – The cookbook archive's URL that you recorded earlier

    Accept the default values for the other settings, and then choose Add Stack to create the stack.

  3. Choose Add a layer, and then add a Java App Server layer to the stack with default settings.

  4. Add a 24/7 instance with default settings to the layer, and then start the instance.

    A t2.micro instance is sufficient for this example.

  5. After the instance is online, connect to it with SSH. The httpd.conf file is in the /etc/httpd/conf directory. The file should contain your custom ErrorDocument setting, which will look something like the following:

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    ... # Some examples: ErrorDocument 500 "A custom error message." #ErrorDocument 404 /missing.html #ErrorDocument 404 "/cgi-bin/missing_handler.pl" #ErrorDocument 402 http://www.example.com/subscription_info.html ...