Cloud-Based Trading Platform Architecture

I'm seeking an expert to design a scalable, secure, cloud-based software architecture for a multi-phase algorithmic trading platform on AWS. The system should incorporate role-based access, modular services, centralized processing, and distributed execution nodes.

Key requirements include:
- AWS cloud architecture
- Implementation in Python
- PostgreSQL for database technology

Ideal skills and experience:
- Expertise in AWS and cloud architecture
- Strong Python programming skills
- Proficiency in PostgreSQL and database management
- Experience in designing secure, scalable systems
- Background in algorithmic trading platforms is a plus