Nested stacks for modularity in AWS - Step-by-Step Execution

Process Flow - Nested stacks for modularity

Start Main Stack

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Define Nested Stack Resources

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Create Nested Stack Template

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Deploy Nested Stack

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Nested Stack Creates Resources

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Main Stack References Nested Stack Outputs

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Complete Deployment

The main stack defines and deploys nested stacks as separate templates, each creating modular resources. Outputs from nested stacks can be referenced by the main stack for integration.

Execution Sample

AWS

MainStack:
  Resources:
    NestedStack1:
      Type: AWS::CloudFormation::Stack
      Properties:
        TemplateURL: nested1.yaml

NestedStack1:
  Resources:
    MyBucket:
      Type: AWS::S3::Bucket

Main stack deploys a nested stack which creates an S3 bucket as a modular resource.

Process Table

Step	Action	Stack	Resource Created	Output Produced	Notes
1	Start deployment	MainStack	None	None	Main stack deployment begins
2	Create NestedStack1 resource	MainStack	NestedStack1 (AWS::CloudFormation::Stack)	None	Nested stack resource defined in main stack
3	Deploy NestedStack1	NestedStack1	S3 Bucket (MyBucket)	BucketName	Nested stack creates S3 bucket resource
4	NestedStack1 outputs BucketName	NestedStack1	None	BucketName: mybucket-123	Output exported for main stack
5	MainStack references NestedStack1 output	MainStack	None	BucketName from NestedStack1	Main stack can use nested stack outputs
6	Complete deployment	MainStack	NestedStack1 and MyBucket	Outputs available	Deployment finished successfully

💡 All nested stacks deployed and outputs referenced; deployment complete

Status Tracker

Variable	Start	After Step 2	After Step 3	After Step 4	Final
MainStack.Resources	{}	{"NestedStack1": "Defined"}	{"NestedStack1": "Deploying"}	{"NestedStack1": "Deployed"}	{"NestedStack1": "Deployed"}
NestedStack1.Resources	N/A	N/A	{"MyBucket": "Created"}	{"MyBucket": "Created"}	{"MyBucket": "Created"}
Outputs.BucketName	N/A	N/A	N/A	"mybucket-123"	"mybucket-123"

Key Moments - 3 Insights

Why does the main stack not create the S3 bucket directly?

Because the S3 bucket is created inside the nested stack (see Step 3 in execution_table), allowing modular separation of resources.

How does the main stack get information about resources created in nested stacks?

Nested stacks export outputs (Step 4) which the main stack references (Step 5) to integrate resources.

What happens if a nested stack deployment fails?

The main stack deployment will fail or roll back because nested stacks are part of the main stack's resource graph.

Visual Quiz - 3 Questions

Look at the execution_table, at which step is the S3 bucket created?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Check the 'Resource Created' column in execution_table rows

According to variable_tracker, what is the state of NestedStack1.Resources after Step 3?

A Undefined

B {}

C {"MyBucket": "Created"}

D {"NestedStack1": "Defined"}

💡 Hint

Look at NestedStack1.Resources row and After Step 3 column

If NestedStack1 did not output BucketName, what impact would it have on the main stack?

A Main stack could not reference the bucket name output

B Nested stack would fail to deploy

C Main stack would create the bucket instead

D No impact, outputs are optional

💡 Hint

Refer to Step 4 and Step 5 in execution_table about outputs and references

Concept Snapshot

Nested stacks let you split big infrastructure into smaller templates.
Main stack deploys nested stacks as resources.
Nested stacks create modular resources independently.
Outputs from nested stacks can be used by main stack.
This improves reusability and organization.
Deployment is atomic: nested stacks are part of main stack.

Full Transcript

Nested stacks help organize cloud infrastructure by splitting it into smaller templates. The main stack defines nested stacks as resources and deploys them. Each nested stack creates its own resources, like an S3 bucket. Nested stacks can output values, such as the bucket name, which the main stack can reference. This modular approach improves clarity and reuse. Deployment proceeds step-by-step: main stack starts, nested stacks deploy their resources, outputs are produced, and main stack uses those outputs. If any nested stack fails, the whole deployment fails. This ensures consistency and modularity in cloud infrastructure management.