google/cadvisor

cAdvisor (short for Container Advisor) is a tool from Google that watches your running containers and tells you exactly how much CPU, memory, network, and disk each one is consuming in real time. If you run applications inside containers, using Docker or a similar system, you need a way to see what those containers are actually doing on the machine. cAdvisor fills that gap by running as a background process alongside your containers, continuously collecting resource usage data and making it available through a web dashboard and a programmable API. It works by reading low-level system information about each container, then organizing that data into historical usage graphs and statistics. You can view the built-in web interface in a browser or connect monitoring tools (like Prometheus) to pull the data automatically. You would use cAdvisor when you are running containers on a server and want to diagnose performance problems, spot a container that is eating too much memory, or feed resource metrics into a larger monitoring setup. It integrates directly with Kubernetes as well, where it can run on every node in a cluster to give cluster-wide visibility. The project is written in Go and can be launched in seconds as a Docker container itself.