Critical Container Basics

Containers run inside NAMESPACES.
Below figure summarizes the concept very well.

Containers are created by using images. Images are selected due to TAGS among many image layers. Image layers occur per build. Differences between builds form a layer. Also when building with a dockerfile, each dockerfile directive create layer for easier visibility. Each layer has UUID. You can examine layers with Dockviz. You can assign any tag to each layer.

Containers may also have storages with COW layer or bind mounts.

Below picture details the concept.(both image layers and storage options)

Some critical container types are also summarized as follows:

- containers running "cloud-native applications" are called "application containers"
- containers running "non-cloud existing applications" are called "pet containers"
- containers running "application" + "virtual operating system" are called "operating system containers"
"virtual operating system" = full INIT cycle to run multiple processes + SYSTEMD to install software
- containers running "with privileges on host kernel" are SPC ( Super Privileged Containers )
E.g: SPC container can load special kernel module SYSTEMTAP
- container with "system software" that MUST run before "container runtime or orchestration"="System Container"
E.g: ETCD must be running for OCP.
E.g: You may require a central SYSLOGD container running first to gather any kind of log.

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