How do you scale a service using Docker Compose?

0-2 years experience

1. 1We have a simple web app defined in a docker-compose.yml with one service. How would you modify the file to run three instances of that service for load handling?
2. 2If you add a `scale` command to `docker-compose up`, what happens to the network ports and how would you expose them to external traffic?
3. 3Which resource limit flags would you set to cap each container's CPU usage when scaling with Compose?

2-5 years experience

1. 1Your team added a new background worker service and you need to run multiple replicas while ensuring they share a common message queue. How would you configure docker-compose to achieve this, and what pitfalls might you encounter?
2. 2During a staging deployment you notice that scaling a stateless API service with `docker-compose up --scale` causes the database connections to exceed the pool limit. How would you troubleshoot and adjust the compose setup?
3. 3Explain why scaling a service with Docker Compose might not be sufficient for high traffic, and what alternatives you would consider.

5-8 years experience

1. 1We need to run a microservice architecture across several hosts, but the team wants to keep using Docker Compose. How would you design a compose‑based solution to scale services across multiple machines, handling service discovery and load balancing?
2. 2When scaling a stateful service like Redis with Docker Compose, what strategies would you employ to ensure data consistency and avoid split‑brain, and how would you monitor it?
3. 3Describe the trade‑offs of using Docker Compose's built‑in scaling versus moving to Docker Swarm or Kubernetes for a high‑throughput e‑commerce platform.

8+ years experience

1. 1Our organization is migrating legacy monolith containers orchestrated with Docker Compose to a cloud‑native platform. How would you plan the transition to a scalable architecture while preserving CI/CD pipelines and minimizing downtime?
2. 2At a company‑wide level, you need to define standards for scaling services with Docker Compose across dozens of teams. What governance, tooling, and documentation would you put in place to ensure consistency and observability?
3. 3If you had to support multi‑region deployments using Docker Compose, what architectural changes and networking considerations would you propose, and how would you handle failover?