Docker - what it is, what it's not

Tit Petrič, @TitPetric

Who am I?

Monotek d.o.o, Dev & Ops
Book author, API Foundations in Go
MMC RTV Slovenia, Lekarna Ljubljana, Kompas
Custom CRM and CMS solutions
golang, php, docker, mysql dba, node,...

Who am I? (cont.)

Engineering blog (Golang, Docker, DevOps...) - https://scene-si.org
API Foundations in Go - https://leanpub.com/api-foundations
Open Source - https://github.com/titpetric
Twitter - https://github.com/titpetric
LinkedIn - https://www.linkedin.com/in/titpetric

Docker

Study the past if you would define the future.

― Confucius

Not a virtual machine

Remember Chroot?

exists since forever (when unix was all there was times)
"filesystem" "isolation" (not really tho)
but then there's memory, cpu, network,...

Not a virtual machine

cgroups (control groups, resource mgmt)

control cpu time share, used cores, affinity
priority - cpu, disk i/o
accounting - see what you use
In the linux kernel since 2006-2007
Initial effort credited to Google
Paul Menage, Rohit Seth

Not a virtual machine

namespaces (isolation)

PID - Process visibility
NET - Network isolation
MNT - Mount point control
IPC - Inter-process communication
USER - User permissions and mapping
UTS - change hostname/domainname

Rob Pike

Plan 9, Bell labs, namespaces in 1992
Since 2005* at Google, co-created Golang '06
Google main contributor of cgroups in '06
Docker is built with Golang

Docker

So what is it not?

It's not an operating system
It's not a virtual machine

Docker

So what is it not?

It's not an operating system
It's not a virtual machine
... but ..
It's kinda like an operating system,
And resource limits are managed like a VM,
It looks and talks like a duck, not a duck

Let's get specific

Resource usage: disk

Virtual Machine: ~10GB - 100GB (OS only, low data)

Docker Image: ~10MB - 100MB - 1GB (Image size, no data)

Docker: True dynamically expanding data (not virtual size of FS)
Image layers: "base" images can be reused
Docker: 1 Application*, VM: 1 Operating system

This is docker

Source: Explaining docker images using Lego, by Graham Dumpleton

This is a virtual machine

Source: Machine Made of Lego Builds Anything You Want — Out of Lego - Wired (MakerLegoBot)

Docker

Docker is the contract between Developers and Operations. Developers and Operations often have very different attitudes when it comes to choosing tools and environments.

― Anders Janmyr

Docker

Microservices based approach, the S in SOLID
Solves version dependency hell, uses whatever
Easy throw-away environments
Migration enabled - on premise, EC2, Azure...

Docker - what it is, what it's not

Docker - what it is, what it's not

Who am I?

Who am I? (cont.)

Docker

Not a virtual machine

Remember Chroot?

Not a virtual machine

cgroups (control groups, resource mgmt)

Not a virtual machine

namespaces (isolation)

Rob Pike

Docker

So what is it not?

Docker

So what is it not?

Let's get specific

Let's get specific

Resource usage: disk

This is docker

This is a virtual machine

Docker

Docker

Questions?

Twitter: Tit Petrič, @TitPetric