Understanding Chef Roles

Lets say that we want to have a couple of cookbooks to be executed on the nodes. In a normal case we can write those cookbooks , upload them to the chef-server. Roles in Chef are way to execute multiple cookbooks at one time on the chef-nodes.

Using Roles , we can logically group machines. Lets say we have a group of machines that run web servers and we want to run some cookbooks on machines that run web servers . in this case we will create a role and set all the cookbooks that need to run on that role ( on those specific set of machines running web servers ). Lastly we will define the machine with that role. In this article we will see an example of using roles,

Create a role using in the ~chef-repo/cookbooks/roles

[root@chefdk roles]# knife role from file web_servers.rb

Updated Role web_servers

Now edit the role as,

[root@chefdk roles]# knife role edit web_servers

This will take you to the web_servers file opened in a vi editor. Edit the content as below,

{

  "name": "web_servers",

  "description": "This role contains nodes, which act as web servers",

  "json_class": "Chef::Role",

  "default_attributes": {

    "ntp": {

      "ntpdate": {

        "disable": true

      }

    }

  },

  "override_attributes": {

  },

  "chef_type": "role",

  "run_list": [

    "recipe[httpd]"

  ],

  "env_run_lists": {

  }

}

In the above snippet of code, I added the line "recipe[httpd]" in the run_list. What iam trying to tell is that nodes which are assigned with the role web_servers, execute this cookbook or receipe httpd. Iam editing the role to define that cookbooks that need to be executed.Edit the Node by adding the role, run the command, knife node edit firstnode

This will open the node in an editor. Make changes as shown in the below content,

{

  "name": "firstnode",

  "chef_environment": "_default",

  "normal": {

    "tags": [

    ]

  },

  "policy_name": null,

  "policy_group": null,

  "run_list": [

  "role[web_servers]"

 ]

}

In the above snippet, I have added the line “role[web_servers]”. Save it.

Once this is done , we attached a role called “web_servers” to the node firstnode. Previously we added the cookbooks that need to run as a part of role. Now lets go to the chef-node and execute the command as,

[root@chefclient ~]# chef-client

[2018-09-04T04:55:04-04:00] INFO: Forking chef instance to converge...

Starting Chef Client, version 12.22.5

[2018-09-04T04:55:04-04:00] INFO: *** Chef 12.22.5 ***

[2018-09-04T04:55:04-04:00] INFO: Platform: x86_64-linux

[2018-09-04T04:55:04-04:00] INFO: Chef-client pid: 23804

[2018-09-04T04:55:04-04:00] INFO: The plugin path /etc/chef/ohai/plugins does not exist. Skipping...

[2018-09-04T04:55:07-04:00] INFO: Run List is [role[web_servers]]

[2018-09-04T04:55:07-04:00] INFO: Run List expands to [httpd]

[2018-09-04T04:55:07-04:00] INFO: Starting Chef Run for firstnode

[2018-09-04T04:55:07-04:00] INFO: Running start handlers

[2018-09-04T04:55:07-04:00] INFO: Start handlers complete.

[2018-09-04T04:55:07-04:00] INFO: HTTP Request Returned 404 Not Found:

[2018-09-04T04:55:07-04:00] INFO: HTTP Request Returned 404 Not Found:

[2018-09-04T04:55:07-04:00] INFO: Error while reporting run start to Data Collector. URL: https://chefserver.nova.com/organizations/nova/data-collector Exception: 404 -- 404 "Not Found"  (This is normal if you do not have Chef Automate)

resolving cookbooks for run list: ["httpd"]

[2018-09-04T04:55:08-04:00] INFO: Loading cookbooks [httpd@0.1.0]

Synchronizing Cookbooks:

  - httpd (0.1.0)

Installing Cookbook Gems:

Compiling Cookbooks...

[2018-09-04T04:55:08-04:00] INFO: HTTP Request Returned 404 Not Found:

Converging 3 resources

Recipe: httpd::default

  * yum_package[httpd] action install[2018-09-04T04:55:08-04:00] INFO: Processing yum_package[httpd] action install (httpd::default line 7)

 (up to date)

  * service[httpd] action enable[2018-09-04T04:55:09-04:00] INFO: Processing service[httpd] action enable (httpd::default line 11)

 (up to date)

  * service[httpd] action start[2018-09-04T04:55:10-04:00] INFO: Processing service[httpd] action start (httpd::default line 11)

 (up to date)

  * cookbook_file[/var/www/html/index.html] action create[2018-09-04T04:55:10-04:00] INFO: Processing cookbook_file[/var/www/html/index.html] action create (httpd::default line 15)

 (up to date)

[2018-09-04T04:55:10-04:00] INFO: Chef Run complete in 2.486547636 seconds

Running handlers:

[2018-09-04T04:55:10-04:00] INFO: Running report handlers

Running handlers complete

[2018-09-04T04:55:10-04:00] INFO: Report handlers complete

Chef Client finished, 0/4 resources updated in 06 seconds

We can see from the output that the chef-client has ran the cookbooks that are defined in the role.