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Regarding the use of three EC2 instances, it's mainly for availability and scalability purposes.
In this setup, we have three instances behind a load balancer to ensure that the application can continue running even if one instance goes down. The load balancer distributes traffic across the three instances, which can handle more load and prevent any single instance from becoming a bottleneck. Additionally, adding more instances can further increase scalability and redundancy.
It's worth noting that the specific number of instances needed may vary depending on the size and requirements of your application. It's important to evaluate your specific needs and make adjustments as necessary.