Module versioning in Terraform - Step-by-Step Execution

Process Flow - Module versioning

Define module source with version

↓

Terraform init downloads module version

↓

Terraform plan uses module version

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Terraform apply deploys infrastructure

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Update version in config to upgrade module

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Terraform init -upgrade upgrades module version

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Terraform apply deploys updated infra

Terraform uses module versioning to control which module code is used during deployment. You specify a version, Terraform downloads that version, and applies it. Updating the version updates the module.

Execution Sample

Terraform

module "vpc" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "3.14.0"
  name    = "my-vpc"
  cidr    = "10.0.0.0/16"
}

This code uses a specific version 3.14.0 of the AWS VPC module to create a VPC named 'my-vpc'.

Process Table

Step	Action	Module Version	Terraform Command	Result
1	Define module with version 3.14.0	3.14.0	terraform init	Module version 3.14.0 downloaded
2	Run terraform plan	3.14.0	terraform plan	Plan created using module 3.14.0
3	Run terraform apply	3.14.0	terraform apply	Infrastructure deployed with module 3.14.0
4	Update module version to 3.15.0	3.15.0	terraform init -upgrade	Module upgraded to 3.15.0
5	Run terraform apply	3.15.0	terraform apply	Infrastructure updated with module 3.15.0
6	No further changes	3.15.0	terraform apply	No changes, infra matches module 3.15.0

💡 Execution stops when infrastructure matches the specified module version and no changes are pending.

Status Tracker

Variable	Start	After Step 1	After Step 4	Final
module_version	undefined	3.14.0	3.15.0	3.15.0

Key Moments - 2 Insights

Why do I need to run 'terraform init' after changing the module version?

Because 'terraform init' downloads the specified module version. Without it, Terraform uses the old version. See execution_table steps 1 and 4.

What happens if I don't specify a version in the module source?

Terraform uses the latest module version available, which can cause unexpected changes. Specifying a version locks the module to a known state.

Visual Quiz - 3 Questions

Look at the execution table, what module version is used during the first 'terraform apply'?

A 3.15.0

B latest

C 3.14.0

D undefined

💡 Hint

Check the 'Module Version' column at step 3 in the execution_table.

At which step does Terraform upgrade the module version?

A Step 2

B Step 4

C Step 5

D Step 6

💡 Hint

Look for 'Module upgraded' in the 'Result' column in execution_table.

If you skip 'terraform init -upgrade' after changing the version, what happens?

A Terraform uses the old module version

B Terraform throws an error

C Terraform uses the new version anyway

D Terraform deletes the module

💡 Hint

Refer to key_moments about why 'terraform init' is needed after version change.

Concept Snapshot

Terraform module versioning:
- Specify 'version' in module block to lock module version
- Run 'terraform init' to download module
- Use 'terraform init -upgrade' to update module version
- Terraform applies infrastructure using specified module version
- Helps keep infrastructure stable and predictable

Full Transcript

Module versioning in Terraform means specifying which version of a module to use in your configuration. When you write a module block with a version, Terraform downloads that exact version during 'terraform init'. Running 'terraform plan' and 'terraform apply' then uses that version to create or update infrastructure. If you want to upgrade the module, you change the version number and run 'terraform init -upgrade' to download the new version. This process ensures your infrastructure uses the module version you expect, avoiding surprises from automatic updates.