Ruby Development - High availability services (Fintech)

Our client, a swedish fintech company in the payment sector, is looking for external support in the development with Ruby.

The team owns two legacy ruby services that they need to make sure work properly during Black Friday 2021 and are deprecated during 2022.
These services store customer's identifiers, personal information and preferences. In the EU, they handle over 100 million records and a peak load of over 3k requests per second. They need to first, make sure that the services are able to withstand the expected increase of traffic during Black Friday without affecting the performance. Then they'd need to migrate data out of them and into the newer services, while occasionally fixing some of the current functionality.

Tasks:
- Fine tune non-rails ruby services to be performant and resilient under high load
- Migrate data into the newer services
- Fixing current functionality