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Terraform - Fundamental

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• Terraform - Fundamental
  • Terraform
    • Installation
    • Command: console
  • HCL
  • Files and Directories
  • Worksapce
  • Debugging Mode

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Terraform

• Infrastructure as code
  • a method of managing and provisioning computing resources using code, rather than manual configuration tools or physical hardware.
• Automation of your infrastructure
• Keep your infrastructure in a certain state (compliant)
  • e.g. 2 web instances with 2 volumes, and 1 load balancer
• Make your infrastructure auditable
  • You can keep your infrastructure change history in a version control system like GIT

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• vs other automation tools

• Ansible, Chef, Puppet, Saltstack have a focus on automating the installation and conguration of software
  • Keeping the machines in compliance, in a certain state
• Terraform can automate provisioning of the infrastructure itself
  • eg. Using the AWS, DigitalOcean, Azure API

• Works well with automation software like ansible to install software after the infrastructure is provisioned先创建基础设施，再自动安装。

• Rel:
  • https://developer.hashicorp.com/terraform/language

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Installation

• Website: https://www.terraform.io/

• 1. Download and unzip
• 1. Place the directory containing terraform.exe in a path.
• 1. Add terraform into PATH.
     • Control Panel > System and Security > System > Advanced system settings
     • Environment Variables > User variables for Administrator
     • Select Path and click Edit
     • Click New and paste the path.
• 1. Test in terminal: terraform version

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Command: console

• terraform console
  • provides an interactive console for evaluating expressions.
• Unavailabel when a specific provider is defined.

terraform console

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HCL

• HCL
  • HashiCorp Conguration Language

• Terraform file extension:

  • .tf

• Terraform language

  • used for declaring resources, which represent infrastructure objects.
  • declarative, describing an intended goal rather than the steps to reach that goal.
  • The ordering of blocks and the files they are organized into are generally not significant;
  • Terraform only considers implicit and explicit relationships between resources when determining an order of operations.
• Terraform configuration
  • a complete document in the Terraform language that tells Terraform how to manage a given collection of infrastructure.
  • A configuration can consist of multiple files and directories.

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• Basic elements:

<BLOCK TYPE> "<BLOCK LABEL>" "<BLOCK LABEL>" {
  # Block body
  <IDENTIFIER> = <EXPRESSION> # Argument
}

• Blocks
  • containers for other content and usually represent the configuration of some kind of object, like a resource.
  • Blocks have a block type, can have zero or more labels, and have a body that contains any number of arguments and nested blocks.
  • Most of Terraform’s features are controlled by top-level blocks in a configuration file.
• Arguments
  • assign a value to a name.
  • appear within blocks.
• Expressions
  • represent a value, either literally or by referencing and combining other values.
  • They appear as values for arguments, or within other expressions.

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Files and Directories

• File Extension

  • Code in the Terraform language is stored in plain text files with the .tf file extension.
  • There is also a JSON-based variant of the language that is named with the .tf.json file extension.

• Configuration files

  • Files containing Terraform code

• Text Encoding

  • Configuration files must always use UTF-8 encoding
  • by convention usually use Unix-style line endings (LF) rather than Windows-style line endings (CRLF), though both are accepted.

• module

  • a collection of .tf and/or .tf.json files kept together in a directory.

• Terraform module

  • only consists of the top-level configuration files in a directory;
    • nested directories are treated as completely separate modules, and are not automatically included in the configuration.
  • Terraform evaluates all of the configuration files in a module, effectively treating the entire module as a single document.
    • Separating various blocks into different files is purely for the convenience of readers and maintainers, and has no effect on the module’s behavior.
  • can use module calls to explicitly include other modules into the configuration.
    • These child modules can come from local directories (nested in the parent module’s directory, or anywhere else on disk), or from external sources like the Terraform Registry.

• Root Module

  • Terraform always runs in the context of a single root module.
  • A complete Terraform configuration consists of a root module and the tree of child modules (which includes the modules called by the root module, any modules called by those modules, etc.).

• In Terraform CLI, the root module is the working directory where Terraform is invoked.

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Worksapce

• Workspace

  • By default, tf starts with a single workspace.
  • isolate the states
    • when creating a new workspace, an empty state will be created.
    • however, still using the same state and same backend configuration (technically equivalent of renaming state file)
  • isolate the resouces
    • the command terraform apply in new workspace will recreate all resources, whose state will be managed in this workspace.

• Varaible terraform.workspace

  • used to avoid naming conllisions
  • used to control resource creation with condition

# avoid naming collision
resource "aws_ssm_parameter" "my-parameter"{
  name = "/myapp/myname-${terraform.workspace}"
}

# conditional
resource "aws_instance" "myinstance" {
  count = terraform.workspace == "default" ? 1 :0
}

• Not Fit

  • workspace cannot be used for a “fully isolated” setup for multiple environment (staging / testing / prod)

• Common Commands

CMD	DESC
terraform workspace new wsp_name	Create a new workspace
terraform workspace select wsp_name	Switch to a workspace

• Use Case

  • useful when needint to test something in the code without making changes to the existing resources.
    • create a workspace to test app and infrastructures before implementing them on existing resources.

• Real world Practises

  • use re-usable modules + multiple remote backend with multi-account strategy
    • staging env:
      • S3 backend with staging AWS account
    • prod env:
      • S3 backend with prod AWS account

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Debugging Mode

• TF just hangs
• set TF_LOG environment variable to enable more loggin.

# Linux
terraform apply -var TF_LOG=DEBUG

# windows Powershell
$Env:TF_LOG="DEBUG"

• Valid log levels:
  • TRACE
  • DEBUG
  • INFO
  • WARN
  • ERROR