CloudFormation template fundamentals

Automating Deployments on AWS

Dunieski Otano

Amazon Web Services Solutions Architect

Why infrastructure as code

• Manual console clicks drift over time
• IaC declares the desired state in a file
• Repeatable, reviewable, versioned
• CloudFormation, SAM, and CDK are the AWS toolkits

CloudFormation template anatomy

• Resources (required): the infra you want to provision
• Parameters: inputs you pass at deploy time
• Outputs: values exported by the stack
• Mappings, Conditions, Transform: helpers (Transform enables SAM)

Intrinsic functions

• Ref: refer to a parameter or another resource
• Fn::GetAtt: read an attribute of a resource
• Fn::Sub: substitute variables into a string
• Short-form: Ref, !GetAtt, !Sub

Change sets preview updates

• A change set previews what an update will do
• Lists every Add, Modify, Remove action
• Flags resources that will be replaced
• Execute or discard, no surprise updates

Drift detection

• Drift: a resource changed outside CloudFormation
• Per-resource status: IN_SYNC, MODIFIED, DELETED, NOT_CHECKED
• Per-resource report shows what differs
• Re-deploy the template to reconcile

Deploying and updating stacks

• Create stack: the first deploy
• Update stack: change resources in place
• Stack events* show every step
• Failed updates roll back to the prior state

Let's practice!

Automating Deployments on AWS