Automatic Provider Cache Dir

This feature has been stabilized and is now enabled by default when using OpenTofu >= 1.10.

Automatic Provider Cache Dir is a feature of Terragrunt that automatically configures OpenTofu’s native provider caching mechanism by setting the TF_PLUGIN_CACHE_DIR environment variable. This enables efficient provider caching without the need to manually configure provider cache directories or use Terragrunt’s provider cache server.

When using OpenTofu >= 1.10, Terragrunt will automatically configure OpenTofu to use a shared provider cache directory, which provides several benefits:

• Improved performance: Providers are downloaded once and reused across multiple configurations
• Reduced bandwidth usage: Eliminates redundant provider downloads
• Better concurrency: OpenTofu 1.10+ handles concurrent access to the provider cache safely
• Simplified setup: No need for manual provider cache configuration

The Automatic Provider Cache Dir feature has specific requirements:

• OpenTofu version >= 1.10 is required
• Only works with OpenTofu (not Terraform)
• If requirements are not met, the experiment silently does nothing

When using OpenTofu >= 1.10, this feature is enabled by default. No additional configuration is required:

terragrunt run --all apply

When enabled, Terragrunt automatically:

1. Detects OpenTofu version and ensures it meets the minimum requirement (>= 1.10)
2. Sets up provider cache directory using the default cache location or a custom path
3. Configures TF_PLUGIN_CACHE_DIR environment variable for OpenTofu processes
4. Ensures directory exists with proper permissions

The default provider cache directory is located at:

• $HOME/.terragrunt-cache/providers on Unix systems
• $HOME/Library/Caches/terragrunt/providers on macOS
• %LocalAppData%\terragrunt\providers on Windows

You can customize the provider cache directory using the --provider-cache-dir flag:

terragrunt apply --provider-cache-dir /custom/path/to/cache

Or with environment variables:

TG_PROVIDER_CACHE_DIR='/custom/path/to/cache' terragrunt apply

You can disable the feature for specific runs using the --no-auto-provider-cache-dir flag:

terragrunt run --all apply --no-auto-provider-cache-dir

This is particularly useful when:

• You want manual control over provider caching for specific environments
• Testing configurations without provider caching
• Using custom provider cache configurations

Terragrunt also provides a Provider Cache Server feature. Here’s when to use each:

Use Auto Provider Cache Dir when:

• Using OpenTofu 1.10+
• You want a simple, low-maintenance caching solution
• You prefer native OpenTofu caching mechanisms
• You need good concurrent access handling

Use Provider Cache Server when:

• Using older versions of OpenTofu/Terraform
• You need advanced caching features
• You want to share providers across different filesystems
• You need custom registry configurations

If the feature doesn’t seem to be working:

1. Check OpenTofu version: Ensure you’re using OpenTofu 1.10 or later
2. Check cache directory: Ensure the cache directory is accessible and has proper permissions
3. Review environment variables: Verify TF_PLUGIN_CACHE_DIR is not already set by another tool

You can enable debug logging to see more information:

terragrunt apply --log-level debug