Content:
-
An image is a lightweight, stand-alone, executable package that includes everything
- needed to run a piece of software, including the code, a runtime, libraries, environment variables
- and config files.
-
A container is a runtime instance of an image—what the image becomes in memory when actually executed.
-
It runs completely isolated from the host environment by default
- only accessing host files and ports if configured to do so.
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Containers run apps natively on the host machine’s kernel.
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They have better performance characteristics than virtual machines that only get virtual access to host
- resources through a hypervisor.
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Containers can get native access, each one running in a discrete process, taking no more memory than
- any other executable.
-
Using containers, everything required to make a piece of software run is packaged into isolated containers.
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Unlike VMs, containers do not bundle a full operating system - only libraries and settings required to make
- the software work are needed.
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This makes for efficient, lightweight, self-contained systems and guarantees that software will always run
- the same, regardless of where it’s deployed.
Consider this diagram comparing virtual machines to containers:
- Virtual machines run guest operating systems—note the OS layer in each box.
- This is resource intensive, and the resulting disk image and application state is an entanglement of OS
- settings, system-installed dependencies, OS security patches, and other easy-to-lose,
- hard-to-replicate ephemera.
- Containers can share a single kernel, and the only information that needs to be in a container image is
- the executable and its package dependencies, which never need to be installed on the host system.
- These processes run like native processes, and you can manage them individually by running commands like
- docker ps—just like you would run ps on Linux to see active processes.
- Finally, because they contain all their dependencies, there is no configuration entanglement;
- a containerized app "runs anywhere."
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