Docker concepts:
Docker is a platform for developers and sysadmins to develop, deploy, and run applications with containers
Containerization's advantages:
- Flexible: Even the most complex applications can be containerized
- Lightweight: Containers leverage and share the host kernel
- Interchangeable: You can deploy updates and upgrades on-the-fly
- Portable: You can build locally, deploy to the cloud, and run anywhere
- Scalable: You can increase and automatically distribute container replicas
- Stackable: You can stack services vertically and on-the-fly
Images and containers
A container is launched by running an image. An image is an executable package that includes everything needed to run an application--the code, a runtime, libraries, environment variables, and configuration files.
A container is a runtime instance of an image--what the image becomes in memory when executed (that is, an image with state, or a user process). You can see a list of your running containers with the command, docker ps, just as you would in Linux.
Containers and virtual machines
A container runs natively on Linux and shares the kernel of the host machine with other containers. It runs a discrete process, taking no more memory than any other executable, making it lightweight.
By contrast, a virtual machine (VM) runs a full-blown “guest” operating system with virtual access to host resources through a hypervisor. In general, VMs provide an environment with more resources than most applications need.
- list the images that was downloaded to your machine
docker image ls
- list containers which exits after displaying its message. If it were still running, you would not need to use --all option
docker container list --all
