Repl.it` is a simple yet powerful in-browser development environment that initially ran only languages that could be compiled to JavaScript and run in the browser, but later expanded to include more features such as filesystem access. The service was built using Go, Docker, and multiple other languages responsible for evaluating code in their respective environments. To scale the service, the author used EC2 instances, which are virtual private servers, and added horizontal scaling by launching multiple machines with the same configuration. They also used AWS's Elastic Load Balancer to distribute traffic across instances and addressed issues such as single point of failure and round-robin routing. The author eventually automated the deployment process using Codedeploy, but encountered issues with visibility over deployments, lack of comprehensive deployment strategies, and bugs in the system. After addressing these issues, they moved on to using Ansible for automation, which allowed them to launch new clusters quickly and easily. The author concluded that scaling a service like Repl.it required a combination of technical expertise, patience, and continuous learning.