11.13 CloudFormation - A Brief Introduction

Introduction

AWS CloudFormation enables you to create and provision AWS infrastructure deployments predictably and repeatedly. It helps you leverage AWS products such as Amazon EC2, Amazon Elastic Block Store, Amazon SNS, Elastic Load Balancing, and Auto Scaling to build highly reliable, highly scalable, cost-effective applications in the cloud without worrying about creating and configuring the underlying AWS infrastructure. AWS CloudFormation enables you to use a Template file to create and delete a collection of Resources together as a single unit (a Stack). For example, a LAMP stack web application with EC2 instances, Auto Scaling group, load balancer, and RDS database. A Template describes all of your resources and their properties.

When you use AWS CloudFormation, you work with templates and stacks. You create templates to describe your AWS resources and their properties. Whenever you create a stack, AWS CloudFormation provisions the resources that are described in your template.

An AWS CloudFormation template is a JSON or YAML formatted text file. You can save these files with any extension, such as .json, .yaml, .template, or .txt. AWS CloudFormation uses these templates as blueprints for building your AWS resources. For example, in a template, you can describe an Amazon EC2 instance, such as the instance type, the AMI ID, block device mappings, and its Amazon EC2 key pair name. Whenever you create a stack, you also specify a template that AWS CloudFormation uses to create whatever you described in the template.

When you use AWS CloudFormation, you manage related resources as a single unit called a stack. You create, update, and delete a collection of resources by creating, updating, and deleting stacks. All the resources in a stack are defined by the stack's AWS CloudFormation template. You can work with stacks by using the AWS CloudFormation console, API, or AWS CLI.

If you need to make changes to the running resources in a stack, you update the stack. Before making changes to your resources, you can generate a Change Set, which is summary of your proposed changes. Change sets allow you to see how your changes might impact your running resources, especially for critical resources, before implementing them.

Template Anatomy

A template is a JSON- or YAML-formatted text file that describes your AWS infrastructure. The following examples show an AWS CloudFormation template structure and its sections. CloudFormation template can be a JSON or YAML formatted text file.

Templates include several major sections. The Resources section is the only required section. Some sections in a template can be in any order:

• Format Version (optional)

  • The AWS CloudFormation template version that the template conforms to. The template format version is not the same as the API or WSDL version. The template format version can change independently of the API and WSDL versions.

• Description (optional)

  • A text string that describes the template. This section must always follow the template format version section.

• Metadata (optional)

  • Objects that provide additional information about the template.

• Parameters (optional)

  • Values to pass to your template at runtime (when you create or update a stack). You can refer to parameters from the Resources and Outputs sections of the template.

• Mappings (optional)

  • A mapping of keys and associated values that you can use to specify conditional parameter values, similar to a lookup table. You can match a key to a corresponding value by using the Fn::FindInMap intrinsic function in the Resources and Outputs section.

• Conditions (optional)

  • Conditions that control whether certain resources are created or whether certain resource properties are assigned a value during stack creation or update. For example, you could conditionally create a resource that depends on whether the stack is for a production or test environment.

• Transform (optional)

  • For serverless applications (also referred to as Lambda-based applications), specifies the version of the AWS Serverless Application Model (AWS SAM) to use.

• Resources (required)

  • Specifies the stack resources and their properties, such as an Amazon Elastic Compute Cloud instance or an Amazon Simple Storage Service bucket. You can refer to resources in the Resources and Outputs sections of the template.

• Outputs (optional)

  • Describes the values that are returned whenever you view your stack's properties. For example, you can declare an output for an S3 bucket name and then call the aws cloudformation describe-stacks AWS CLI command to view the name.

JSON-formatted Template Sample:

{
  "AWSTemplateFormatVersion" : "version date",

  "Description" : "JSON string",

  "Metadata" : {
    template metadata
  },

  "Parameters" : {
    set of parameters
  },

  "Mappings" : {
    set of mappings
  },

  "Conditions" : {
    set of conditions
  },

  "Transform" : {
    set of transforms
  },

  "Resources" : {
    set of resources
  },

  "Outputs" : {
    set of outputs
  }
}

Pricing

There is no additional charge for AWS CloudFormation. You pay for AWS resources created using AWS CloudFormation in the same manner as if you created them manually.

Trouble Shooting

The newly created stack may have some problems, if you build a wordpress website and you cannot visit your website, you maybe facing some network problems. You can go to check the security groups inbound and outbound rules for the EC2 instances. You can also go to check which security group is associated with these EC2 instances or ELB.