What role do containers (Docker) play in microservices?

Docker containers are the natural packaging format for microservices. A container bundles a service's code, runtime, libraries, and configuration into a single, portable image that runs identically in development, testing, and production. Each microservice becomes its own Docker image, and multiple services can run on the same host without interfering with each other's dependencies. Docker eliminates the "it works on my machine" problem by encapsulating all dependencies. When combined with an orchestrator like Kubernetes, containers can be automatically scheduled, scaled, restarted on failure, and updated with zero-downtime rolling deployments, making Docker's container model foundational to operating microservices at scale.