Kubernetes
Container orchestrator, an open source project (Apache 2.0 licence) hosted by the Cloud Native Computing Foundation. You describe the wanted state ("three copies of this app") and it holds to it: it restarts containers that fail or miss their health check, adds or removes copies according to load, and spreads traffic between them. It does not build your app: it assumes container images already exist, made with Docker or an equivalent.
Strengths
- Self-healing: restarts failed containers and keeps unready ones out of traffic
- Horizontal scaling: more or fewer copies, by hand or based on CPU load
- Built-in service discovery and load balancing, so traffic does not overload a single copy
Limitations
- Heavy learning curve: a vocabulary of its own (pods, deployments, services) before the first result
- Does not build or deploy your source code, and is not a turnkey platform: you plug your delivery chain into it
- Oversized below a handful of services: a host or Docker Compose suffice far longer than people think
Best for
- Teams operating dozens of containerised services in production
- Designers and product managers who must follow an infrastructure discussion without being lost in it