Template anatomy

Resources, and the sections around them.

Beginner12 min · lesson 2 of 12

A CloudFormation template is a structured document — YAML (preferred, readable) or JSON — with a fixed set of top-level sections. Only Resources is required; the rest are optional scaffolding around it. Resources is where you declare each AWS resource by a logical ID, its Type (the AWS resource kind), and its Properties. References between resources build the dependency graph, exactly like other IaC tools.

template.yaml

AWSTemplateFormatVersion: "2010-09-09"
Description: A logging bucket with versioning
 
Resources:
  LogsBucket:
    Type: AWS::S3::Bucket
    Properties:
      BucketName: acme-logs-prod
      VersioningConfiguration:
        Status: Enabled
      PublicAccessBlockConfiguration:
        BlockPublicAcls: true
        BlockPublicPolicy: true
        IgnorePublicAcls: true
        RestrictPublicBuckets: true

The sections around Resources

The optional sections make a template reusable and expressive: Parameters take input at deploy time, Mappings are lookup tables (e.g. AMI per region), Conditions gate whether resources are created, Outputs export values (and can be imported by other stacks), and Metadata/Transform add tooling hints and macros. You will meet each, but the mental model is: Resources is the what, everything else shapes how it is parameterized and wired.

Template sections

required

Resources

the AWS resources to create

common optional

Parameters

deploy-time inputs

Mappings / Conditions

lookups + gating

Outputs

export values

Transform

SAM / macros

Start with Resources; add sections as the template needs inputs, logic, or exports.

Prefer YAML, and validate before deploy

YAML templates support comments and short-form intrinsic functions (!Ref, !Sub) that make them far more readable than JSON. Whatever you write, run aws cloudformation validate-template (and cfn-lint) before deploying — a template that is syntactically valid can still be caught early for bad references and property types, saving a failed stack and a rollback.

What CloudFormation is & the modelParameters, mappings & outputs