Containers are an increasingly used mechanism for providing low-cost, lightweight, portable, standalone application deployments, particularly for service orchestration. Docker provides container technology that enables a single host to isolate several applications and deploy them rapidly in different environments. The increasing demand for container applications and the growing popularity of Docker has motivated extensive research into evaluating the performance, energy consumption, and running cost of Docker-based computation. This paper investigates the energy footprint of Docker containers and workloads. To motivate research in energy-efficient container development, this paper takes a practical approach to measure the energy consumption in common Docker containers under various workloads.