Debugging Chef Recipes on AWS OpsWorks – Access Custom JSON and Data Bag Attributes

Edit This question and answer are years old. The definitive best practices are taught via the Learn Chef Rally self-paced training modules produced by Chef Software, Inc. The bulk of the original answer is below.

In this answer, "Chef" or "chef-client" usually refers to Chef Infra, the product. Opscode renamed to Chef Software, Inc in 2013. In April, 2019, Chef opened the source code for all its products, along with creating consistent brand naming.

Not clear if it's better to setup roles in ruby DSL, JSON, or from the management console? Why are there multiple ways to do the same thing?

2019 Update: Policyfiles are the best workflow to use. Roles are considered an inferior practice, and Chef Software, Inc. recommends migrating to Policyfiles.

There are multiple ways to do the same thing because people have different workflows. You pick the workflow that is best for your environment. Let me explain what the differences are so you can make an informed decision.

The Ruby DSL for Roles exists to make it easier to write roles without knowing the syntax of JSON. It is a simple way to get started with Roles. Once you have made changes, you upload them to the Chef Server with knife.

knife role from file myrole.rb

This converts the role to JSON and stores it on the server. If you have an environment that enforces the Chef Repository where your roles live as the source of truth, this works quite well.

JSON is what the Chef Server stores, so you also edit JSON directly in the management console. It does require more fields than the Ruby DSL in order for Knife to recognize it properly to upload. Those details are hidden to some degree via the web UI.

The disadvantage of using the webui/management console for editing roles is they aren't in your local version control system unless you download them from the server. You can do this with knife:

knife role show myrole -Fj

The -Fj tells knife to "display in JSON format." You can redirect the output to a .json file if you like.

Years ago update: There are additional knife commands for working with the files in the local chef repository. Currently these commands support only JSON format files. A community RFC is open which will address adding support for the Ruby DSL for these plugins. Here's a brief summary of the workflow.

Check content differences between the server and the local file.

knife diff roles/myrole.json

Upload a JSON formatted role file. The roles/ path is required. This gets mapped to the same API endpoint on the server.

knife upload roles/myrole.json

Download the content from the server overwriting the content of the file in the repository.

knife download roles/myrole.json

These commands come from knife-essentials, which is built into the chef client package.

Can you organize cookbooks into subdirectories? eg- we have custom software that I'd like to write a cookbook for and stick that into: chef-repo/cookbooks/ourcompanystuff/customsoftwarecookbook would this be a good practice?

No. Knife has an expectation of where cookbooks should live because it uses an API to upload cookbooks to the Server. This is set in the knife.rb with cookbook_path. In older versions of Chef Infra, you could specify an array of paths for cookbooks, but this is being deprecated because it required more maintenance and was confusing to users.

By convention we name customer specific or site specific cookbooks with the name prefixed in the cookbook diretory. For your example, it would be:

chef-repo/cookbooks/ourcompany_customsoftware

There might be multiple different cookbooks for "ourcompany" depending on what you're doing.

Further reference:

• https://docs.chef.io/cookbooks.html
• https://learnchef.com

Do I create a cookbook for each type of role that specifies what it does? Do I have these cookbooks include other cookbooks (i.e.- the cookbook for my webserver role includes the apache cookbook). I'm not sure how cookbook inter-dependencies and inheritance are handled.

There is no direct relationship or dependency between roles and cookbooks.

Roles have a run list, which specifies the recipes and other roles that should be applied to any node that has that role. Nodes have a run list that can contain roles or recipes. When Chef runs on the node, it will expand the run list for all the roles and recipes it includes, and then download the cookbooks required. In a node run list:

recipe[apache2]

Chef will download the apache2 cookbook for the node so it can apply this recipe.

You might have a cookbook specific for a role in your infrastructure. More commonly you'll have cookbooks that are for setting up certain types of services like apache2, mysql, redis, haproxy, etc. Then you would put those into appropriate roles. If you have custom application specific things that need to happen to fulfill a role, then you could write this into a custom cookbook (like I referenced above).

Further reference:

• http://docs.chef.io/roles.html
• https://docs.chef.io/config_rb_metadata.html

Is there anything like puppets external node classifier so nodes automatically determine their roles?

"Yes." The Chef Infra Server does node data storage (in JSON) automatically, and the server also automatically indexes all the node data for search.

Further reference:

• https://docs.chef.io/nodes.html
• https://docs.chef.io/chef_search.html

It seems like you can configure things with knife or within the management console, or editing JSON files? This is super confusing to me why there are so many ways to do things, it's paralyzing! Is there a reason to use one or the other?

The Chef Infra Server has a RESTful API that sends and receives JSON responses. Knife and the management console are user interfaces for interacting with the API from an administration point of view.

You can use the tool you like better, though the management console doesn't have as many features as Knife. Most people that use Chef Infra prefer the command-line interface for the power and flexibility it provides, even folks who are using Chef Infra on Windows. Further, knife is a plugin based tool that you can create new plugins to interact with the Chef Infra Server, or with other parts of your infrastruture.

Chef Infra is a set of libraries, primitives, and an API. It gives you the flexibility to build the configuration management system that works best for your infrastructure.

Further reading:

• https://docs.chef.io/knife.html

How can I automatically provision nodes with chef in my dev cluster? With puppet I fire up a VM that connects to the puppermatser and kicks off a puppet run and sets itself up (role is determined by external node classifier). How do I do this with chef? - Install chef with pem/rb files that tie it to a chef server, manually tell the node its roles with knife or editing this in the management interface, and then kicking off a chef-client run to set itself up?

You'll want to use the knife bootstrap plugin. This is a built in plugin that comes with knife. You invoke it like this:

knife bootstrap 10.1.1.112 -x root -i ~/.ssh/root_id_rsa -r 'role[webserver]'

This will:

• SSH to the target system (10.1.1.112) as the root user using an SSH key (you could ssh as another user and then use --sudo).
• Install Ruby
• Install Chef
• Create the Chef configuration file for your Chef Server, reading knife's configuration (.chef/knife.rb).
• Copy the "validation" RSA private key, which the node will use to automatically register with the Chef Server.
• Run chef-client using the comma separated run listed specified. In this example only the webserver role is applied.

This assumes that the target system has been provisioned, has an IP address and you can SSH as root. Depending on your local policies and provisioning process, you may need to adjust how this works. The knife bootstrap page on the wiki describes more about how this works.

Knife also has plugins for a number of public cloud computing providers such as Amazon EC2 and Rackspace Cloud. There are plugins available for private cloud environments like Eucalyptus and OpenStack. There are also plugins for VMware, Vsphere and others. You can see further information in the documentation.

Further reading:

• https://docs.chef.io/knife_bootstrap.html
• http://docs.chef.io/chef_client.html
• https://speakerdeck.com/jtimberman/anatomy-of-a-chef-run-and-authentication-cycle-1
• https://docs.chef.io/auth.html
• http://lists.opscode.com/sympa/arc/chef-dev/2011-08/msg00055.html
• https://docs.chef.io/plugin_knife.html
• https://docs.chef.io/plugin_knife_custom.html

Are there any other good chef resources I might be missing in my searches?

The Chef Documentation the primary source of documentation.

The Learn Chef Rally is a series of self-guided modules that you can learn all about various aspects of Chef Infra, and other Chef products.

I used to maintain a blog where I posted tips, tricks, and guides about Chef Infra: http://jtimberman.housepub.org/. I had a series called "quick tips". Due to real life circumstances and other commitments, I no longer have time to maintain the site, but I may return to it in the future.

Chef customers can get help and support on the support site:

• https://www.chef.io/support/

The Chef user community is an excellent source of additional help:

• https://www.chef.io/community/

Additional resources are available on Chef Software, Inc.'s web site.

I hope this helps.

I'm not so keen on the total_memory idea it's somewhat of an indirect quantity. Maybe it makes more sense in the context of whatever the magical daemon is though.

For tunable attributes like total memory, I pretty much would do as you have laid out in the question by adding a sensible default value to attributes/default.rb (cuts down on support questions when someone forgets to explicitly set a value) and override with environment, role or node-specific values where necessary.

It's possible to do arithmetic inside the ERB file like this:

memory = <%= (node['memory']['total'][0..-3].to_i / 1024) * 
             node['magical-daemon']['memory'] %>

Ohai makes available the statistics from free(1) which includes the total memory in kB. node['memory']['total'] = '12312432kB' on my workstation.

I also try and use attributes with the lowest priority as much as possible, i.e prefer default over normal attributes, and normal attributes over override attributes. So,

• choose a sensible recipe default where possible
• use a default environment attribute (you use an override attribute in the example)
• use a role attribute for groups of nodes (again you use an override attribute)
• and finally default node attribute

See the attribute precedence link in the Chef wiki) for the order in which attributes override each other.

Using the lowest precedence default attributes where possible allows you to set the attribute value depending on the environment, role and node, but frees up the upper levels of precedence when you need to do something tricky.