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Inside Docker

Inside Docker

A small overview of virtualization technics and their schemes of work, as well as the internal structure of Docker (LXC plus AUFS)

Anton Kaliaev

January 30, 2014

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  1. User Apps Ring 3 Ring 2 Guest OS Ring 1

    VMM Ring 0 Hardware Binary translation Full virtualization using Binary translation
  2. User Apps Ring 3 Ring 2 Ring 1 Paravirtualized Guest

    OS Ring 0 Hardware Replacing non-virtualizable OS-instructions Paravirtualization Virtualization Layer
  3. User Apps Ring 3 Ring 2 Ring 1 Guest OS

    Ring 0 Hardware x86 VMM Root mode privilege levels Non-root mode privilege levels
  4. To summarize VBox ‣ Emulates IO/Hardware devices, BIOS ‣ Use

    binary translation ‣ Work hard in MMU (shadowing pages table, updating TLB)
  5. ‣ Kernel namespaces (ipc, uts, mount, pid, network and user)

    ‣ AppArmor and SELinux profiles ‣ Seccomp policies ‣ Chroots (using pivot_root) ‣ Kernel capabilities ‣ Control groups (cgroups)
  6. Cgroups Resource limiting CPU Memory IO cpu.shares cpuset.cpus memory.limit_in_bytes blkio.throttle.

    {read,write}. {iops,bps}.device blkio.weight memory.stat cpuacct.stat Accounting Isolation
  7. ‣ The liblxc library ‣ Several language bindings (python3, lua

    and Go) ‣ A set of standard tools to control the containers ‣ Container templates Parts
  8. ‣ all containers uses the same kernel ‣ thus requires

    less resources ‣ and more lightweight ‣ takes seconds to start (fast) Pros ‣ not so isolated Cons
  9. AUFS Branch 1 Branch 2 f1 f1 f2 f2 f3

    f3 f3 d1 f4 f5 d1 f4 d1 f5 f6 f6 f6 Copy on Write Write Read
  10. ‣ storage savings ‣ faster deployments ‣ better memory usage

    ‣ easier upgrades ‣ allows arbitrary changes (root filesystem is still writeable) Pros ‣ not so active development Cons
  11. Resources 1. VMware “Understanding Full Virtualization, Paravirtualization, andHardware Assist” http://www.vmware.com/files/pdf/

    VMware_paravirtualization.pdf 2. Namespaces in operation, part 1: namespaces overview https://lwn.net/ Articles/531114/ 3. PaaS Under the Hood http://blog.dotcloud.com/ 4. Lightweight Virtualization by Jérôme Petazzoni http:// www.socallinuxexpo.org/sites/default/files/presentations/Jerome- Scale11x%20LXC%20Talk.pdf 5. The File system http://www.tldp.org/LDP/tlk/fs/filesystem.html