Optimize, and redesign to use AWS features. Just dumping your existing code on EC2 is often a bad idea.
We worked with a client and analyzed their workload and software. With a few minor changes we could reduce their always on EC2 instances with 66%. They where not interested. Then at least buy reserved instances? Nope, also not interested.
For sure. And making sure you aren't using them inefficiently. At one point we were using 30% of our AWS spend doing S3 API calls. The next day it was 1% by optimizing that.
We were using S3 as ternary storage for our time series database by moving values from the secondary SSD based storage to S3. Each of those values contained all the values for a full day. By using HTTP range queries and placing an index in the SSD store we were able to combine 30 days of values into a single S3 value to decrease the API PUT calls by 30x.
We worked with a client and analyzed their workload and software. With a few minor changes we could reduce their always on EC2 instances with 66%. They where not interested. Then at least buy reserved instances? Nope, also not interested.