Terraform Basics

Disadvantages of Data Center Deployment

1. Time to set up
2. Many manual steps involved
3. Under utilization of resources e.g. unused web sites during night time
4. Costly

IaC (Infrastructure as Code)

Hence IaC comes into picture which is API based and provisions resources in cloud  environment.

Basically it can configures the entire provisioning environment.

Types of infrastructure components are web servers, databases, networks

3 types of Iac

1. Configuration Management

1. Ansible
2. Puppet
3. SaltStack

     on existing Infrastructure componenets.

2. Server Templating

1. Docker
2. Packer
3. Vagrant

Usually create images on VM or containers

3. Provisioning Tools

1. Terraform
2. Cloud Formation

Provision Infrastructure components using simple declarative code.

Terraform - Infrastructure Provisioning tool for various cloud platforms.

Providers

Providers enable Terraform to provision various infrastructure components.

• Infrastructure Components on cloud platforms
• Network Components - BigIp, Infoblox
• Data Diagnostics and Monitoring tools - DataBag, Grafana
• Databases - MySql, MongoDB
• VCS (Version Control Systems) - Github, Bitbucket

HCL (HashiCorp Configuration Language)

File extension - .tf

Terraform Stages

1. INIT - Initializes project directory and identifies set of providers. Downloads and installs plugins for providers.
2. PLAN - Create plan to achieve target state on target environment.
3. APPLY - Makes changes to achieve the desired state on target environment.

Terraform scripts are used to Provision, Configure and Decommission Resources.

Terraform manages states of resources & remembers them as they are in existence. Imports state of other resources and manages them as well.

How to install Terraform

Terraform binary or zip can be downloaded from www.terrafor.io and installed on the deployment environment. 

Structure  of Terraform Files

main.tf

    

        <block> <parameters>{

                key1 = value1

                key2 = value2

        }

        e.g. resource (block name) local_file (provider_resouceType) resource_name{

                Arguments

            }

    Arguments are key value pairs which depend upon the resource type.

Providers

Available in registry.terraform.io maintained by Hashicorp

Official Providers - aws, azure, local

Verified Providers - Partner providers (3rd party) e.g. Heroku

Complementary Providers - provided by individual contributors of hashicorp community.

Providers are installed in .terraform/plugins

Location of official providers - registry.terraform.io/hashicorp/local (hostname/organizational namespace/provider)

Location of veirified providers registry.terraform.io/<org namespace>/heroku 

Sets cannot have duplicate values, lists can.

Automatically loaded varibles - terraform.tfvars or terraform.tfvars.json, **.auto.tfvars or **.auto.tfvars.json

All other .tfvars files must be specified as command line argument in tarraform apply -var-file command.

Variable Precedence in Terraform

=> command line with -var or -var-file

=> ***.auto.tfvars or ***.auto.tfvars.json

=> terraform.tfvars or terraform.tfvars.json

=> environment variables - export TF_VARS_variableName = "value"

Explicit Dependency

Each resource created by Terraform will have a unique id which terraform will store in the resource's state file.

Terraform state will provide the following benefits:

* keeps a cache of the resource's atttributes and will identify which resources to change correctly based in dependencies

* terraform plan -refresh=false will only rely on local state copy and doesn't refresh state from actual resources. Performant!

Terraform state is the single point of truth of the state of the real world resources.

Terraform state files contain sensitive information and should be stored in remote secured storage such as AWS, Azure, Terraform Cloud.

Terraform refresh will refresh state file from real world resources if any changes. It'll not change configuration files.