DevOps Classroom Series – 12/Sept/2020 – Direct DevOps from Quality Thought

Chef Infra Server Components

Infra Components Refer Here

Creating Lab Environment

In this scenario
- PROD: will be Ubuntu 18 machines from aws
- UAT: Will be Ubuntu 18 machines from aws
- QA: Will be Ubuntu 18 machine from azure
Upload qthms-app and qthms-db to the chef server

Now lets bootstrap manually all the nodes from workstation to nodes
Lets bootstrap chef server in the qa, uat and prod environments
Lets try to come up with run_list for every node

QA : qthms-app::default,qthms-db::default

uat
	app: qthms-app::default
  
	db: qthms-db::default
  
prod:
	app: qthms-app::default
	
	db: qthms-db::default

In a large kind of deployment, managing run_lists is not effecient by add recipes to every node.
To manage this lets create two roles
1. appserver
2. dbserver
Roles can be created from chef-manage.
But it is a good practice to have version control of your roles. so lets create roles files in chef-repo
For Roles Official docs Refer Here

Lets create two roles in the roles folder with the following content for

appserver.rb

name  'appserver'
description 'This is qthms appserver'
run_list 'qthms-app::default'

dbserver.rb

name  'dbserver'
description 'This is qthms  dbserver'
run_list 'qthms-db::default'

Now lets upload the roles to the chef server

knife role from file <path-to-rb>

Preview

Now lets edit run lists to have the roles in the run_list rather than recipes
Now the convergence time is 30 minutes for all the servers. Now lets learn how to change that
Client Configurations can be changed from client.rb file in the chef repo refer Here or easier way is to add the following cookbook to the run_list refer Here

# first approach
Chef::Config[:interval] = <seconds>

To do common configuration lets create a cookbook qt-general
In this cookbook lets add dependency of chef-client and set the attribute

default['chef_client']['interval']= '1800'

Now we need to add this recipe to all the nodes, we have roles, go and change the roles
For app servers the interval should be ‘3600’ seconds for db servers the convergence should be ‘7200’
The appserver.rb (role)

name  'appserver'
description 'This is qthms appserver'
run_list 'qt-general::default', 'qthms-app::default'
default_attributes(
    'chef_client' => {
        'interval' => '3600'
    }
)

Role db server

name  'dbserver'
description 'This is qthms dbserver'
run_list 'qt-general::default','qthms-db::default'
default_attributes(
    'chef_client' => {
        'interval' => '7200'
    }
)

Now we need to add a new version of the cookbook to include java ’11’ and also install apache server
Now make changes and after successful testing of this cookbook if you upload changes it will be applied to all servers in appserver role which is not what we want.
We want this changes to be applied only to QA, SO this is where environments come into play. \
Like Roles environments can be created from manage, inside chef-repo Refer Here
By default chef has a environment already called as _default
Now lets create 3 environment files in environments folder in chef repo
- qa.rb
- uat.rb
- prod.rb
Refer to git for these files
Lets upload the environments

knife environment from file <path-to-env>

Preview Preview

Lets apply environments to the nodes
Now upload the cookbook
Verify the QA Environment
Verify in other Environment
Now we have multiple places where we define attributes
- recipe
- attribute file
- roles
- environments
Lets understand what gets applied.
Chef has an extra layer which is attribute types
- default
- force_default
- normal
- override
- force_override
- automatic
We have 4 different places and six different types where attributes can be defined
Chef follows the following table for precedence
Refer Here for offical docs
Note: GitHub Link Refer Here