What challenges have you faced migrating legacy applications to the cloud and how did you resolve them

What challenges have you faced migrating legacy applications to the cloud, and how did you resolve them?

Migrating legacy applications to the cloud brings out a special set of issues, involving compatibility, refactoring, data migration, and integrating with modern cloud services. This question looks to uncover specific issues during cloud migration projects and how you approached overcoming them, including best practices or tools that aided the transition and optimized performance in the cloud.