Learning about CloudFormation

• It is a AWS service
• It simplifies Infrastructure Management
• Used to model and set up AWS resources
• Involves creating  template which lists AWS resources needed
• responsible for provisioning and configuring AWS resources
• Used by Elastic Beanstalk
• Cloud formation (CFN) template describes all needed resources and their properties.
• Template
  • has JSON format
  • JSON document gives instructions for CFN
  • Instructions on resources to act and what resources to create/update
• Stack 
  • refers to CFN unit of grouping infra
• Stack Policy
  • IAM style policy
  • governs what or who can change
  • can be added via CLI or UI
  • updated but cannot be removed
• Create CFN template -> Add template to CFN -> Create CFNStack -> Resources (200 per template) -> Update template/Stack -> Delete Stack
• Template components
  • Parameters  – used to pass variables into template
  • Mappings (allow processing of hash’s by CFN template)
  • Resources,
  • Outputs (results from template);
  •  Only Resources is mandatory.
  • CFN can run scripts within instances, expand files within instances, stack id(unique).
• Use cases:
  • Template for manual deployment of bespoke infra.
  • create repeatable patterned environment (ex:wordpress site with DB)
  • run automated testing for CI/CD environments (dev, test, prod)
  • define an environment once, deployed
  • manage infra config using software development style versioning and testing concepts.
• It provisions
  • Auto Scaling group
  • load balancer
  • and database
• Can easily edit or delete resources  
• manage a collection of resources as a single unit or stack.
• Quickly replicate infrastructure
• control and track changes to infrastructure

CloudFormation Working

• Easily create an infrastructure stack, with CloudFormation by
  • making underlying service calls to AWS
  • provision and configure AWS resources.
• calls are as per defined template.
• CloudFormation perform only actions having permission to do.
• CloudFormation template can be a JSON or YAML-formatted document
• After all resources have been created, AWS CloudFormation reports stack creation
• If stack creation fails, CloudFormation rolls back changes by deleting the resources that it created.

Steps

• Design an CloudFormation template in AWS CloudFormation Designer or text editor.
• Save template either in s3 or locally
• Create an AWS CloudFormation stack by specifying the location of template file

Change Sets

• It is a summary of proposed changes to stack
• Used for stack updation
• stack updation is done to reflect changes on resources being used
• Before making changes, generate a change set
• Change sets enables seeing impact of change on running resources, before implementing them.
• Updates can cause interruptions, depending on resource and properties being updated
• Change sets do not indicate successful stack update.
• Example, changing Amazon RDS database instance name,
  • CloudFormation will create a new database and delete the old one and and will lose data in old database
  • With change set, see changes on database to be replaced, and plan accordingly

Updating a Stack with Change Sets

• To update stack’s resources, modify stack’s template.
• Do not create new stack and delete old one.
• Instead, create change set by submitting a modified version of original stack template,
• CloudFormation compares the modified with original template and generates a change set.
• Change set lists the proposed changes.
• After reviewing changes, execute the change set to update stack

Steps

• Modify CloudFormation stack template using CloudFormation Designer or a text editor.
• Save CFN template can be saved either to s3 bucket or locally
• changeset is created to reflect any changes needed in stack
• View changeset to check CloudFormation will perform with the changes
• Execute changeset to apply to stack.

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