What are health checks in Docker?

Health checks in Docker are essential mechanisms that allow the Docker engine to assess the operational state of a container. Specifically, these checks involve executing a specified command within the container at defined intervals to verify if the application is functioning as intended. If the command returns a successful exit status, the container is considered healthy. Conversely, if it fails after a number of retries, Docker marks the container as unhealthy.

This mechanism is vital for ensuring application reliability, allowing other services or orchestration tools to take appropriate actions if a container is deemed unhealthy, such as restarting it or alerting developers. The ability to monitor the health of containers helps maintain overall system stability and performance, providing a systematic way to manage application lifecycle events effectively.

In contrast, the other options refer to different aspects of container and network management rather than the specific purpose and function of health checks in Docker. For instance, commands that remove unhealthy containers pertain to container lifecycle management, while metrics that monitor network performance and settings that define resource limits are more aligned with network and resource management rather than health verification.