Chef data bags can be defined as an arbitrary collection of data which one can use with cookbooks. Using data bags is very helpful when one does not wish to hardcode attributes in recipes nor to store attributes in cookbooks.

Working Method

In the following setup, we are trying to communicate to http endpoint URL. For this, we need to create a data bag, which will hold the endpoint URL detail and use it in our recipe.

Step 1 − Create a directory for our data bag.
mma@laptop:~/chef-repo $ mkdir data_bags/hooks
Step 2 − Create a data bag item for request bin. One needs to make sure one is using a defined requestBin URL.
vipi@laptop:~/chef-repo $ subl data_bags/hooks/request_bin.json {
"id": "request_bin",
"url": "http://requestb.in/1abd0kf1"
}
Step 3 − Create a data bag on the Chef server
vipin@laptop:~/chef-repo $ knife data bag create hooks
Created data_bag[hooks]
Step 4 − Upload the data bag to the Chef server.
vipin@laptop:~/chef-repo $ knife data bag from file hooks requestbin.json
Updated data_bag_item[hooks::RequestBin]
Step 5 − Update the default recipe of the cookbook to receive the required cookbook from a data bag.
vipin@laptop:~/chef-repo $ subl cookbooks/my_cookbook/recipes/default.rb
hook = data_bag_item('hooks', 'request_bin')
http_request 'callback' do
url hook['url']
end
Step 6 − Upload the modified cookbook to the Chef server.
vipin@laptop:~/chef-repo $ knife cookbook upload my_cookbook
Uploading my_cookbook [0.1.0]
Step 7 − Run the Chef client on the node to check if the http request bin gets executed.
user@server:~$ sudo chef-client
...TRUNCATED OUTPUT...
[2013-02-22T20:37:35+00:00] INFO: http_request[callback]
GET to http://requestb.in/1abd0kf1 successful
...TRUNCATED OUTPUT...

How it Works

Data bag is a named collection of structure data entries. One needs to define data entry and call the data bag item in JSON file. One can also search for data bag item from within the recipes to use the data stored in the data bags.
We created a data bag called hooks. A data bag is a directory within Chef repository. We used knife to create it on the server.

Chef – Scripts for Data Bugs

In certain conditions, it is not possible to put the server under the full control of Chef. In such cases, one might need to access values in Chef data bags from scripts. In order to do this, one needs to store data bag values in a JSON file and let the added script access those values.
For this, one needs to have a cookbook. In our case we would use test_cookbook as earlier and should have the run list of the node including test_cookbook definition in it.

Working Method

Step 1 − Create a data bag.
vipin@laptop:~/chef-repo $ mkdir data_bags/servers
vipin@laptop:~/chef-repo $ knife data bag create servers
Created data_bag[servers]
Step 2 − Create a data bag item.
vipin@laptop:~/chef-repo $ subl data_bags/servers/Storage.json {
"id": "storage",
"host": "10.0.0.12"
}
Step 3 − Update the data bag item.
vipin@laptop:~/chef-repo $ subl data_bags/servers/Storage.json {
"id": "storage",
"host": "10.0.0.12"
}

Using in Cookbook

Step 1 − Need to create a JSON file containing data bag values using the above cookbook so that external scripts can access those values.
vipin@laptop:~/chef-repo $ subl cookbooks/test_cookbook/recipes/default.rb
file "/etc/backup_config.json" do
owner "root"
group "root"
mode 0644
content data_bag_item('servers', 'backup')['host'].to_json
end
Step 2 − Upload test_cookbook to Chef server.
vipin@laptop:~/chef-repo $ knife cookbook upload test_cookbook
Uploading my_cookbook [0.1.0]
Step 3 − Run the Chef client on the node.
user@server:~$ sudo chef-client
...TRUNCATED OUTPUT...
[2013-03-14T20:30:33+00:00] INFO: Processing
file[/etc/backup_config.json] action create
(my_cookbook::default line 9)
[2013-03-14T20:30:34+00:00] INFO: entered create
[2013-03-14T20:30:34+00:00] INFO:
file[/etc/backup_config.json] owner changed to 0
[2013-03-14T20:30:34+00:00] INFO:
file[/etc/backup_config.json] group changed to 0
[2013-03-14T20:30:34+00:00] INFO:
file[/etc/backup_config.json] mode changed to 644
[2013-03-14T20:30:34+00:00] INFO:
file[/etc/backup_config.json] created file
/etc/backup_config.json
...TRUNCATED OUTPUT...
Step 4 − Validating the content of the generated JSON file.
user@server:~$ cat /etc/backup_config.json
"10.0.0.12"

Workflow of Scripts

In the above command, the file resource that we have used which creates JSON file inside the /etc directory is defined in the default cookbook. It gets the file content directly from the data bag using the data_bag_item method. We access the host values from the data bag item and convert it to JSON. The file resource uses the JSON-converted values as its content and writes it to the disk.

So, this brings us to the end of blog. This Tecklearn ‘Concept of Data Bags in Chef’ blog helps you with commonly asked questions if you are looking out for a job in DevOps. If you wish to learn Chef and build a career in DevOps domain, then check out our interactive, Continuous Delivery using Chef Training, that comes with 24*7 support to guide you throughout your learning period. Please find the link for course details:
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