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Containers

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DISCLAIMER

Container = OCI compliant container (e.g Docker container).

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What a container is not ?!

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Containers vs VMs: the bad analogy

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Wrong again: containers are running on/by the kernel (not on the CE)

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Confusion

  • How to SSH into a container ?
  • How to execute more than one CMD per container ?
  • How come the container exits after docker run ps <img> ?
  • How to provision (Ansible, Chef …) my docker container ?
  • Why shouldn’t I install my deps directly in the container using �docker exec -it <container> apt install <pkg> Instead of using images and Dockerfiles ?
  • ….

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What is a container ?

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Containers are nothing but “special” linux processes

  • Linux technologies
    • Namespaces (PID, UID, MOUNT, NET …)
    • Chroot
    • Cgroups
    • SELinux, AppArmor
    • Capabilities
    • SECCOMP
  • “Linux containers” is not a real thing !!

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Why are containers compared to VMs ? (OS virtualization Era)

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Container lifecycle

Container registry

Remote repository

local repository

Container Host

image

pull

image

create

start

run

stop

rm

kernel

fs

pull

extend

mount

Spec file

run

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Running Containers

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Container runtime

Container engine

Container daemon

Container cli

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Case Study: PBS (container-tools)

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System container runtimes: LXC/LXD, OpenVZ ...