Why a container loses its data when it restarts Write a row to a database running in a Docker container, stop the container, start it again: the row is gone. Every container gets its filesystem fresh from its image each time it starts. Anything the container itself writes — database files, uploads, logs — goes into a writable layer that is thrown away when the container is removed. A Docker volume is how you keep that data outside the container, where it survives. ...

What Docker actually does Docker is an open source platform that packages an application with everything it needs to run — code, libraries, runtime, configuration — into a container that behaves the same on any machine. Moving house makes the trade-off concrete. You have two options: Carry all your belongings loose, hoping they arrive intact Put everything in organized, labeled boxes that are easy to move Docker does exactly this with software applications: it “packages” them into containers that contain everything they need to run. ...

What Kubernetes does One Docker container on one machine is easy to run by hand. Fifty containers across ten machines — restarting them when they crash, moving them when a machine dies, splitting traffic between them, updating them without downtime — is not. Kubernetes (shortened to K8s) is the system that does that managing for you. What Is Kubernetes? Kubernetes is an open-source platform for container orchestration. Google created it in 2014 based on 15 years of running containers at scale, and the Cloud Native Computing Foundation (CNCF) maintains it now. ...