State and real infrastructure mapping in Terraform - Step-by-Step Execution

Process Flow - State and real infrastructure mapping

Terraform Config Files

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terraform apply

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Terraform State File

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Compare State vs Real Infrastructure

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No Action

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Update State File

Terraform reads config files, applies changes, updates state file, and compares state with real infrastructure to keep them in sync.

Execution Sample

Terraform

terraform apply
# Terraform reads config
# Checks state file
# Compares with real infra
# Creates/updates resources
# Updates state file

This simulates Terraform applying infrastructure changes and updating its state file to match real resources.

Process Table

Step	Action	State File Content	Real Infrastructure	Result
1	Read config files	State file with previous resources	Existing cloud resources	Prepare plan
2	Compare state with real infra	State shows resource A exists	Resource A exists	Match - no change
3	Compare state with real infra	State shows resource B exists	Resource B missing	Diff - resource B to create
4	Create missing resource B	State updated to include resource B	Resource B created in cloud	State and infra synced
5	Finish apply	State file fully updated	Real infra matches state	Apply complete

💡 All resources in config are created or updated; state file matches real infrastructure.

Status Tracker

Variable	Start	After Step 2	After Step 4	Final
State File	{"resources": ["A", "B"]}	{"resources": ["A", "B"]}	{"resources": ["A", "B"]}	{"resources": ["A", "B"]}
Real Infrastructure	{"resources": ["A"]}	{"resources": ["A"]}	{"resources": ["A", "B"]}	{"resources": ["A", "B"]}

Key Moments - 2 Insights

Why does Terraform create resource B even though it is not in the real infrastructure?

Because the state file expects resource B to exist (see step 3 in execution_table), Terraform detects the difference and creates it to match the state.

What happens if the real infrastructure has a resource not in the state file?

Terraform will detect this as a difference and may try to remove or import it depending on configuration, ensuring state and real infra match.

Visual Quiz - 3 Questions

Look at the execution table, at which step does Terraform detect a missing resource in real infrastructure?

A Step 3

B Step 2

C Step 4

D Step 5

💡 Hint

Check the 'Result' column in execution_table rows for where 'Diff - resource B to create' appears.

According to variable_tracker, what resources exist in real infrastructure after step 4?

A ["A"]

B ["A", "B"]

C ["B"]

D []

💡 Hint

Look at the 'Real Infrastructure' row under 'After Step 4' in variable_tracker.

If resource B was already present in real infrastructure at start, how would step 3 change?

A Terraform would delete resource B

B It would still show 'Diff - resource B to create'

C It would show 'Match - no change'

D Terraform would error out

💡 Hint

Refer to step 3 in execution_table where comparison happens between state and real infra.

Concept Snapshot

Terraform uses a state file to track real infrastructure.
When you run 'terraform apply', it compares the state file with actual resources.
If differences exist, Terraform creates, updates, or deletes resources to match the state.
After changes, Terraform updates the state file to reflect reality.
This keeps your infrastructure and state in sync.

Full Transcript

Terraform manages infrastructure by keeping a state file that records what resources exist. When you run terraform apply, it reads your configuration files and compares the state file with the actual cloud resources. If it finds differences, such as missing resources, it creates or updates them. After making changes, Terraform updates the state file to match the real infrastructure. This process ensures your infrastructure matches your configuration and state file.