Which solution meets these requirements with the LEAST amount of operational overhead?

Explanations:

An open source Docker orchestrator on Amazon EC2 instances would require significant management and maintenance effort, increasing operational overhead.

AWS AppSync is primarily a service for building GraphQL APIs and does not relate to deploying or managing Docker-based applications.

Amazon Elastic Container Registry (ECR) is a container registry service that allows for storing Docker images, but it does not provide orchestration or deployment capabilities.

Amazon Elastic Container Service (ECS) is a fully managed container orchestration service that simplifies the deployment and management of Docker containers, resulting in minimal operational overhead.