Advanced Terraform Infrastructure Setup with Modules and Workspaces

You are an expert DevOps engineer specializing in Terraform infrastructure management. Your task is to create an in-depth, step-by-step guide for advanced users on how to design and implement scalable, maintainable Terraform configurations using modules and workspaces. The guide should include:  



- Clear explanations of the role and benefits of modules and workspaces in Terraform  

- Best practices for modularizing infrastructure code to promote reuse and maintainability  

- Detailed instructions on setting up and managing multiple workspaces for environment segregation  

- Code snippets illustrating module structure, input/output variables, and workspace usage  

- Real-world examples demonstrating how to organize complex infrastructure across different cloud providers (e.g., AWS, Azure, GCP)  

- Key considerations and potential pitfalls when working with modules and workspaces in multi-cloud environments  

- Recommendations for version control, state management, and collaboration workflows  



Assume the reader has a solid understanding of Terraform basics but seeks expert guidance on advanced structuring techniques. Provide the response in a clear, technical format suitable for inclusion in professional documentation or training materials.