Docker

Agenda

• History
  • Virtualization
  • Containers
  • Docker
• Use Case (and concerns)
• Architecture
• Demos

Ancient History

• Long, long ago there was chroot.
• Not quite so long ago there was dual-boot...
  and multi-boot.
• Eventually, we had virtualization.
• But, full blown virtual machines can be space hogs.

Virtual Machines

Evolution to Containers

• But if on one host we have many co-located VMs, it seems really wasteful to have so many copies of that guest OS.
• Furthermore, if the guest OS is the same as the host OS, why do we need ANY copy? Isn't most of it the same?
• Different OS's started to address this in slightly different ways.

Containers

• FreeBSD created "jails".
• Solaris (and variants) gave us "zones". And "ZFS" deduplication addressed the storage issue.
• Linux created "containers" (a couple kinds actually).
• All of these are like VM solutions but where the host and guest are the same thing.

Recap

Union File System

• Several Linux Container solution(s) took advantage of another innovation:
  Union File System.
• The idea here is to have a read-only file system "underneath" a writable file system".
• Any file operation that "reads" looks at the top layer first.
• Writes only occur at the top layer.
• You can have several read-only layers stacked.

on to Docker

• Docker grew out of LXC and UFS
• Docker provided a layered system architecture based on UFS
• Docker became very popular because it introduced a repository system for containers like GitHub
• Docker containers differ from Virtual Machines and general containers in that (for the most part) a Docker container is just one app.

Docker grows to
non-Linux

• A host OS can run a guest container if it has the core of the guest OS builtin.
• Solaris did this supporting CentOS (Linux) in its Zones.
• Now, both Windows and MaxOS support Docker.

Why use Docker

• Speed of Implementation. The Docker Ecosystem may already have the app you need, preconfigured and ready to deploy almost immediately.
• Ease of extending. You can take a container, build upon it and create your own template for future containers.
• Segmentation of Concerns. An update or removal of one app doesn't force you to endure "Dependency Hell".

When to avoid Docker

• Security.
• GUI (eg. X11)

Docker Architecture

• Images
• Containers

Additional Topics

• Virtual Networking
• Using images to "snapshot" a container.
• Ferry
• Docker within Docker