DevOps Classroom notes 17/Dec/2023

Dealing with Declarative Languages

• Any Declartive Language is all about expressing the desired state.
• Most of the tools in Azure, AWS and DevOps use the following languages primarily for desired state
  • HCL (Hashicorp Configuration Language)
  • Json (ARM Templates, Cloud Formation)
  • Bicep
  • YAML (Ansible, K8s)
• Our focus is around Infra Provisioning

Datatypes

• text
• number
• boolean
• list/array
• map/object
• Terraform data types: Refer Here
• map in json

{
    "networkrange": "10.10.0.0/16",
    "subnetcount": 4
}

• map in terraform

{
    networkrange = "10.10.0.0/16"
    subnetcount = 4
}

Resources

• The infra we want to create for the application to be deployed
• ARM Template (json)

{
    "type": "<type>",
    "apiVersion": "2019-06-01",
    "properties": {
         "accessTier": "Hot"
    }

}

• Cloud formation (json)

"Logical ID" : {
        "Type" : "Resource type",
        "Properties" : {
            Set of properties
        }
    }

• Example:

"mys3":  {
    "Type": "AWS::S3::Bucket",
    "Properties" : {
        "BucketName" : "idontwants3bucket"
    }

}

• Cloud formation (yaml)

Logical ID:
  Type: Resource type
  Properties:
    Set of properties

• Example in yaml

mys3:
  Type: "AWS::S3::Bucket"
  Properties:
    BucketName: "idontwants3bucket"

• HCL (Terraform)

resource "aws_s3" "mys3" {
    bucket = "idontwants3bucket"
}

Parameters

• these are the values which can be passed by user during execution. In terraform we refer the same as variable.
• JSON in ARM Refer Here

"parameters" : {
    "location": {
        "type": "string" //,
        //"allowedValues": ["eastus", "westus"]
        //"defaultValue": "eastus"
    }
}

• Using this parameter reference in azure "[parameters('location')]"
• JSON in CF

"Parameters" : {
  "InstanceTypeParameter" : {
    "Type" : "String",
    "Default" : "t2.micro",
    "AllowedValues" : ["t2.micro", "m1.small", "m1.large"],
    "Description" : "Enter t2.micro, m1.small, or m1.large. Default is t2.micro."
  }
}

• Using this parameter reference in cf {"Ref": "InstanceTypeParameter" }
• Variable in Terraform

variable "instancetype" {
    type = "string"
    default = "t2.micro"
}

• Using this varaible reference in terraform var.instancetype

Functions

• Refer Here for functions in ARM Templates and Refer Here here for cloudformation function
• Refer Here for terraform functions
  

conditions and loops

• Terraform conditions Refer Here
• Refer Here for looping expressions

Reusability

• In terraform we create modules
• Both ARM Templates and Cloud formation supports calling other templates.