Stacks, Parameters, and Outputs

A Stack is CloudFormation's fundamental unit of management — every resource defined in a template becomes part of that stack when deployed, and CloudFormation tracks the relationship between the stack and its resources, enabling operations on the whole group at once (update everything together, or delete everything together cleanly).

Parameters let a template accept input values at deployment time rather than hardcoding them — an instance type, an environment name, a database password (ideally referenced from Secrets Manager rather than passed as plain text) — making the same template genuinely reusable across different environments or accounts by supplying different parameter values each time, rather than needing a separate, duplicated template per environment.

Outputs let a stack expose specific values (like a created load balancer's DNS name, or a VPC's ID) for use outside the stack — either for a human to reference, or, more powerfully, for a different CloudFormation stack to import via cross-stack references, enabling infrastructure to be split into logically separate, more manageable stacks (e.g. a networking stack and an application stack) that still reference each other's resources cleanly.

Parameters:
  EnvironmentName:
    Type: String
    AllowedValues: [dev, staging, prod]
  InstanceType:
    Type: String
    Default: t3.micro

Resources:
  WebServer:
    Type: AWS::EC2::Instance
    Properties:
      InstanceType: !Ref InstanceType
      Tags:
        - Key: Environment
          Value: !Ref EnvironmentName

Outputs:
  InstanceId:
    Value: !Ref WebServer