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An **orchestrator** is a system that **manages containers** across a cluster of servers: it starts, stops, scales, and monitors them.
It automates everything that is impossible to do manually with dozens of microservices.

### Main tasks of an orchestrator

1. **Deploying containers**
It distributes containers across nodes (servers) itself, choosing where resources are available.
2. **Scaling**
It increases or decreases the number of service instances as load changes.
3. **Monitoring and self-healing**
It tracks the state of containers and automatically restarts ones that have crashed.
4. **Load balancing**
It distributes requests among the running service instances.
5. **Configuration and secrets management**
It stores environment variables, tokens, and passwords and injects them into containers at startup.
6. **Zero-downtime updates (rolling updates)**
It gradually replaces old container versions with new ones without interrupting service.

### Orchestrator examples

- **Kubernetes**: the most popular, with a mature ecosystem.
- **Nomad (HashiCorp)**: lightweight, simple to configure.
- **Amazon ECS / EKS**: managed solutions on AWS.

**Summary:**

> An orchestrator is the "operating system" for microservices.
> It ensures their stable operation, scaling, and automation, freeing the team from the routine of managing containers.

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