I helped a startup in the health sector with their fast growing needs for their architecture on AWS. In the first stage i brought their running stack up to security standards with correct VPC, improved Security groups and actual correct Roles for services.
The second step was to develop a target Architecture for their heavy fluctuating data-processing needs. One week theres not a lot of data to be processed, next week they have a dataset of multiple hundred-thousand that needs to be processed and enriched in a short timeframe. All of that in a cost-efficient way was the major challenge that I tackled with this customer.