What is the MOST cost-effective way for the company to handle the sudden and significant changes in traffic?

Explanations:

Adding read replicas can help with read scalability but will not solve the write-heavy issues since writes still go to the primary instance. Purchasing Instance Savings Plans and RDS Reserved Instances may reduce costs but does not address the irregular load effectively.

Migrating to an Aurora multi-master DB cluster can improve write scalability, but it does not directly address cost-effectiveness for irregular workloads. Instance Savings Plans do not provide significant cost savings in this context.

An Aurora global database is designed for global applications with low-latency read access but may not be the most cost-effective solution for irregular workloads. Purchasing Compute Savings Plans and RDS Reserved Instances may help in cost reduction but not in handling sudden load changes.

Migrating to Aurora Serverless v1 allows the database to automatically scale up and down based on demand, making it ideal for irregular workloads. This provides cost savings as you only pay for what you use, and purchasing Compute Savings Plans can further reduce costs.