How to fix Error: Module not installed in Terraform

Execute the terraform init command in your working directory. This command initializes Terraform, installs all required providers, and downloads all referenced modules:

terraform init

This is the most common solution. Terraform will scan your configuration files, find all module references, and download them into the .terraform/modules directory.

Check your .tf files for module declarations. Ensure the source path is correct:

module "example" {
  source = "./modules/my-module"  # Local module
}

module "vpc" {
  source  = "terraform-aws-modules/vpc/aws"  # Registry module
  version = "~> 5.0"
}

module "network" {
  source = "git::https://github.com/org/repo.git//modules/network"  # Git module
}

Common issues:
- Typos in the source path
- Incorrect case (especially on case-sensitive filesystems)
- Missing the double slash (//) for subdirectories in Git modules
- Outdated or incorrect Git repository URLs

If the error persists after checking the module sources, the cache may be corrupted. Remove it and reinitialize:

rm -rf .terraform
rm .terraform.lock.hcl
terraform init

This removes the cached modules and lock file, forcing Terraform to re-download everything fresh.

If you recently changed module version constraints, use the -upgrade flag to force Terraform to check for newer versions:

terraform init -upgrade

This is useful when:
- You updated version constraints in your module block
- You want to fetch the latest compatible version
- Previous module versions are cached but no longer valid

For remote modules (from Git or the Terraform Registry), verify:

1. Internet connectivity: Ensure your system can reach the module source:

ping github.com

2. Git authentication (for private repositories): Configure Git credentials:

git config --global credential.helper store
git clone <your-private-repo>

3. Terraform Registry access: The public registry at registry.terraform.io should be accessible. If you use a private registry, configure it in your .terraformrc:

credentials "app.terraform.io" {
  token = "YOUR_API_TOKEN"
}

4. Firewall/proxy rules: Ensure no firewall blocks access to module sources.

Run terraform validate to catch syntax errors in your configuration:

terraform validate

This checks for:
- Invalid module block syntax
- Undefined variable references
- Missing required arguments
- Circular dependencies

Fix any reported errors before running terraform init again.