netwyman

Some Docker instructions look similar and cause confusion among developers who just started using Docker or do it irregularly. In this post I will explain the difference between CMD, RUN, and ENTRYPOINT on examples. In a nutshell RUN executes command(s) in a new layer and creates a new image. E.g., it is often used for installing software packages. CMD sets default command and/or parameters, which can be overwritten from command line when docker container runs. ENTRYPOINT configures a container that will run as an executable. If it doesn’t make much sense or you after details, then read on. Docker images and layers When Docker runs a container, it runs an image inside it. This image is usually built by executing Docker instructions, which add layers on top of existing image or OS distribution. OS distribution is the initial image and every added layer creates a new image. Final Docker image reminds an onion with OS distribution inside and a number of layers on top of it. For ex...