Step 15: Update the Cookbook to Use Conditional Logic

Important

The AWS OpsWorks Stacks service reached end of life on May 26, 2024 and has been disabled for both new and existing customers. We strongly recommend customers migrate their workloads to other solutions as soon as possible. If you have questions about migration, reach out to the AWS Support Team on AWS re:Post or through AWS Premium Support.

Now update your cookbook by adding a recipe that uses conditional logic, a technique that runs code only if certain conditions are met. For more information, go to if Statements and case Statements.

This recipe does two things based on data bag content: displays a message in the log identifying the operating system that the instance is running on and, only if the operating system is Linux, installs a package by using the correct package manager for the given Linux distribution. This package is named tree; it is a simple app for visualizing directory lists.

To update the cookbook on the instance and to run the new recipe

1. On your local workstation, in the recipes subdirectory in the opsworks_cookbook_demo directory, create a file named conditional_logic.rb that contains the following code:

   instance = search("aws_opsworks_instance").first
   os = instance["os"]
   
   if os == "Red Hat Enterprise Linux 7"
     Chef::Log.info("********** Operating system is Red Hat Enterprise Linux. **********")
   elsif os == "Ubuntu 14.04 LTS" || os == "Ubuntu 16.04 LTS" || os == "Ubuntu 18.04 LTS"
     Chef::Log.info("********** Operating system is Ubuntu. **********") 
   elsif os == "Microsoft Windows Server 2012 R2 Base"
     Chef::Log.info("********** Operating system is Windows. **********")
   elsif os == "Amazon Linux 2015.03" || os == "Amazon Linux 2015.09" || os == "Amazon Linux 2016.03" || os == "Amazon Linux 2016.09" || os == "Amazon Linux 2017.03" || os == "Amazon Linux 2017.09" || os == "Amazon Linux 2018.03" || os == "Amazon Linux 2"
     Chef::Log.info("********** Operating system is Amazon Linux. **********")
   elsif os == "CentOS Linux 7"
     Chef::Log.info("********** Operating system is CentOS 7. **********")
   else
     Chef::Log.info("********** Cannot determine operating system. **********")
   end
   
   case os
   when "Ubuntu 14.04 LTS", "Ubuntu 16.04 LTS", "Ubuntu 18.04 LTS"
     apt_package "Install a package with apt-get" do
       package_name "tree"
     end
   when "Amazon Linux 2015.03", "Amazon Linux 2015.09", "Amazon Linux 2016.03", "Amazon Linux 2016.09", "Amazon Linux 2017.03", "Amazon Linux 2017.09", "Amazon Linux 2018.03", "Amazon Linux 2", "Red Hat Enterprise Linux 7", "CentOS Linux 7"
     yum_package "Install a package with yum" do
       package_name "tree"
     end
   else
     Chef::Log.info("********** Cannot determine operating system type, or operating system is not Linux. Package not installed. **********")
   end

2. At the terminal or command prompt, use the tar command create a new version of the opsworks_cookbook_demo.tar.gz file, which contains the opsworks_cookbook_demo directory and its updated contents.

3. Upload the updated opsworks_cookbook_demo.tar.gz file to your S3 bucket.

4. Follow the procedures in Step 5: Update the Cookbook on the Instance and Run the Recipe to update the cookbook on the instance and to run the recipe. In the "To run the recipe" procedure, for Recipes to execute, type opsworks_cookbook_demo::conditional_logic.

To test the recipe

1. With the Running command execute_recipes page displayed from the previous procedures, for cookbooks-demo1, for Log, choose show. The execute_recipes log page is displayed.

2. Scroll down through the log and find an entry that looks similar to the following:

   [2015-11-16T19:59:05+00:00] INFO: ********** Operating system is Amazon Linux. **********

   Because the instance's operating system is Amazon Linux 2016.09, only the preceding entry (of the five possible entries in the recipe's code) will be displayed in the log.

3. If the operating system is Linux, the recipe installs the tree package. To see a visualization of a directory's contents, type tree at the command prompt from the desired directory or with the desired directory's path (for example, tree /var/chef/runs).

In the next step, you will update the cookbook to use functionality from an external cookbook provided by the Chef community.