Docker - How to Get Started

All images copyright Docker Inc.

Ben Webber walks through how to get started using Docker for application virtualization.

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2. Outline 1. What is Docker? 2. Use cases 3. Containers vs. VMs 4. Terminology 5. Docker images are like onions 6. Dockerfiles 7. Security 8. Getting started 9. Demo: Hello world! 10. Further reading 2 / 17
3. What is Docker? Docker is a container virtualization tool built on native Linux APIs. Docker... automates deploying applications inside containers provides access to kernel APIs using libcontainer (Docker 1.0) or native LXC (older releases) must run on a Linux host can only run Linux containers Docker is not necessarily a replacement for full virtualization. 3 / 17
4. Use cases deploy self-contained, isolated application stacks build self-contained development environments (some overlap with Vagrant) spin up continuous integration environments continuous delivery test on different distributions build applications for different package managers In general, Docker excels at building discrete, non-stateful application stacks. You would not use Docker to deploy persistent components like databases. 4 / 17
5. + - - - - - - - - - - - - - - + - - - - - - - - - - - - - - + | | | | u s e r l a n d | u s e r l a n d | | | | + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + | | | | k e r n e l | k e r n e l | | | | + - - - - - - - - - - - - - - + - - - - - - - - - - - - - - + | | | h y p e r v i s o r | | | + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + VM completely isolated kernel and userland dedicated resources hypervisor can support multiple operating systems as guests + - - - - - - - - - - - - - - + - - - - - - - - - - - - - - + | | | | u s e r l a n d | u s e r l a n d | | | | + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + | | | c o n t a i n e r l a y e r | | | + - - - - - - - - - - - - - - + - - - - - - - - - - - - - - + | | | k e r n e l | | | + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + Container shares kernel space with other instances higher density due to lower overhead guests must be the same operating system as the host Containers vs. VMs 5 / 17
6. Image A read-only layer in the union filesystem. Images are the product of a chain of saved changes, all the way back to a parent image. Container A writable layer on top of an image. Containers: preserve state (run status) include metadata about the instance (e.g., resource allocations) Terminology 6 / 17
7. Docker images are like onions Docker uses a union filesystem (AuFS), which allows several filesystems to be mounted simultaneously. Docker images are layers in the union filesystem. Each layer has a direct ancestor (parent image). Only the topmost layer (the container) is writable. 7 / 17
8. Docker images are like onions Individual layers are “committed” to the filesystem. When building an image, Docker applies each change in sequence. Updating an existing image is very speedy, since the lower layers have not changed. $ d o c k e r h i s t o r y g o I M A G E C R E A T E D C R E A T E D B Y S I Z E f a a 5 1 0 3 1 5 1 c 2 A b o u t a n h o u r a g o / b i n / s h - c # ( n o p ) E N T R Y P O I N T [ / w w w / a p p ] 0 B 5 b c 3 a 9 2 2 7 3 3 0 A b o u t a n h o u r a g o / b i n / s h - c g o b u i l d a p p . g o 8 . 2 2 5 M B 3 3 f 1 8 2 a 5 1 2 a a A b o u t a n h o u r a g o / b i n / s h - c # ( n o p ) W O R K D I R / w w w 0 B e 5 e c b 9 4 2 b 6 c e A b o u t a n h o u r a g o / b i n / s h - c g o g e t g i t h u b . c o m / z e n a z n / g o j i 1 . 9 5 3 M B c 0 8 4 2 8 9 0 3 2 8 7 A b o u t a n h o u r a g o / b i n / s h - c # ( n o p ) E N V G O P A T H = / g o 0 B a 8 a 6 2 1 9 e 5 d 4 f A b o u t a n h o u r a g o / b i n / s h - c # ( n o p ) A D D d i r : d 2 d 2 8 c 8 2 5 4 5 6 0 3 d e c 0 4 1 7 . 9 1 M B c 5 b 9 f d 5 a 3 3 a c A b o u t a n h o u r a g o / b i n / s h - c a p t - g e t i n s t a l l - y g o l a n g g i t 2 1 1 . 4 M B 1 7 2 5 6 f c 9 5 2 8 6 A b o u t a n h o u r a g o / b i n / s h - c a p t - g e t u p d a t e 4 . 3 1 3 M B e 5 4 c a 5 e f a 2 e 9 3 w e e k s a g o / b i n / s h - c a p t - g e t u p d a t e & & a p t - g e t i n s t a l l 1 7 8 . 4 k B 6 c 3 7 f 7 9 2 d d a c 3 w e e k s a g o / b i n / s h - c a p t - g e t u p d a t e & & a p t - g e t i n s t a l l 8 3 . 6 1 M B 8 3 f f 7 6 8 0 4 0 a 0 3 w e e k s a g o / b i n / s h - c s e d - i ' s / ^ # \ s * \ ( d e b . * u n i v e r s e \ ) $ / 1 . 9 0 3 k B 2 f 4 b 4 d 6 a 4 a 0 6 3 w e e k s a g o / b i n / s h - c e c h o ' # ! / b i n / s h ' > / u s r / s b i n / p o l i c 1 9 4 . 5 k B d 7 a c 5 e 4 f 1 8 1 2 3 w e e k s a g o / b i n / s h - c # ( n o p ) A D D f i l e : a d c 4 7 d 0 3 d a 6 b b 2 4 1 8 e 1 9 2 . 5 M B 5 1 1 1 3 6 e a 3 c 5 a 1 3 m o n t h s a g o 0 B In the history above, the highlighted lines represent commits introduced while building the Go image from the demo. 8 / 17
9. Dockerfiles Docker can read the steps necessary to build an image from a Dockerfile. A Dockerfile is simply a text file with instructions. Each step runs independently, adding a commit to the image history. F R O M u b u n t u # I n s t a l l s y s t e m d e p e n d e n c i e s R U N a p t - g e t u p d a t e R U N a p t - g e t i n s t a l l - y g o l a n g g i t # I n s t a l l t h e a p p l i c a t i o n c o d e A D D . / w w w # I n s t a l l G o d e p e n d e n c i e s E N V G O P A T H / g o R U N g o g e t g i t h u b . c o m / z e n a z n / g o j i # B u i l d t h e a p p W O R K D I R / w w w R U N g o b u i l d a p p . g o # R u n t h e a p p E N T R Y P O I N T [ " / w w w / a p p " ] 9 / 17
10. Security Containers share the same kernel space, and thus could be affected by vulnerabilities allowing arbitrary code execution. To isolate containers, Docker: gives containers have individual kernel namespaces for accessing resources allocates resources using Linux c g r o u p s , limiting DOS attacks prunes unnecessary kernel capabilities (even if the container is running as r o o t , it does not have the same access as the r o o t on the host) There is at least one published exploit affecting pre-1.0 releases. 10 / 17
11. Getting started Install Docker. $ b r e w i n s t a l l d o c k e r Since Docker only runs on Linux, you need to run the containers inside a VM. Vagrant has built-in support for deploying Docker containers, but you can also use boot2docker. For the demo, we'll use Vagrant. $ b r e w t a p c a s k r o o m / c a s k $ b r e w c a s k i n s t a l l v a g r a n t v i r t u a l b o x 11 / 17
12. Design Sinatra app listening on 0 . 0 . 0 . 0 : 8 0 0 0 Docker container exposes port 8 0 0 0 as l o c a l h o s t : 9 0 0 0 on the host HAProxy on the Vagrant VM forwards HTTP requests to l o c a l h o s t : 9 0 0 0 Structure ├── V a g r a n t f i l e ├── a p p │ ├── D o c k e r f i l e │ ├── G e m f i l e │ └── a p p . r b └── v a g r a n t └── p u p p e t ├── f i l e s │ └── h a p r o x y . c f g ├── f i l e s e r v e r . c o n f ├── m a n i f e s t s └── s i t e . p p Hello world! We'll use Docker to provision a simple “Hello world!” app on a Vagrant VM. 12 / 17
13. Hello world! Vagrantfile V A G R A N T F I L E _ A P I _ V E R S I O N = " 2 " V a g r a n t . c o n f i g u r e ( V A G R A N T F I L E _ A P I _ V E R S I O N ) d o | c o n f i g | c o n f i g . v m . b o x = " t r u s t y 6 4 " c o n f i g . v m . n e t w o r k " f o r w a r d e d _ p o r t " , g u e s t : 8 0 , h o s t : 8 0 8 0 # I n s t a l l a n d c o n f i g u r e H A P r o x y c o n f i g . v m . s y n c e d _ f o l d e r " v a g r a n t / p u p p e t " , " / e t c / p u p p e t " c o n f i g . v m . p r o v i s i o n " p u p p e t " d o | p u p p e t | p u p p e t . m a n i f e s t s _ p a t h = " v a g r a n t / p u p p e t / m a n i f e s t s " p u p p e t . m a n i f e s t _ f i l e = " s i t e . p p " p u p p e t . o p t i o n s = " - - v e r b o s e - - f i l e s e r v e r c o n f i g = / e t c / p u p p e t / f i l e s e r v e r . c o n f " e n d # P r o v i s i o n t h e S i n a t r a a p p c o n f i ] . v m . p r o v i s i o n " d o c k e r " d o | d o c k e r | d o c k e r . b u i l d _ i m a g e " / v a g r a n t / a p p " , a r g s : " - t a p p " d o c k e r . r u n " a p p " , a r g s : " - p 9 0 0 0 : 8 0 0 0 " e n d e n d 13 / 17
14. Application r e q u i r e ' s i n a t r a ' s e t : b i n d , ' 0 . 0 . 0 . 0 ' s e t : p o r t , 8 0 0 0 g e t ' / ' d o " p u t s ' H e l l o w o r l d ! ' " e n d Dockerfile F R O M u b u n t u # I n s t a l l s y s t e m d e p e n d e n c i e s R U N a p t - g e t u p d a t e R U N a p t - g e t i n s t a l l - y r u b y R U N g e m i n s t a l l b u n d l e r # I n s t a l l a p p l i c a t i o n c o d e A D D . / w w w # I n s t a l l R u b y d e p e n d e n c i e s W O R K D I R / w w w R U N b u n d l e i n s t a l l # R u n t h e a p p E N T R Y P O I N T [ " r u b y " , " / w w w / a p p . r b " ] Hello world! 14 / 17
15. Hello world! Ship it $ v a g r a n t u p $ h t t p l o c a l h o s t : 8 0 8 0 H T T P / 1 . 1 2 0 0 O K C o n n e c t i o n : c l o s e C o n t e n t - L e n g t h : 4 8 C o n t e n t - T y p e : t e x t / h t m l ; c h a r s e t = u t f - 8 D a t e : F r i , 1 1 J u l 2 0 1 4 1 5 : 0 1 : 0 3 G M T S e r v e r : W E B r i c k / 1 . 3 . 1 ( R u b y / 1 . 9 . 3 / 2 0 1 3 - 1 1 - 2 2 ) X - C o n t e n t - T y p e - O p t i o n s : n o s n i f f X - F r a m e - O p t i o n s : S A M E O R I G I N X - X s s - P r o t e c t i o n : 1 ; m o d e = b l o c k p u t s ' H e l l o w o r l d ! ' 15 / 17
16. Hello world! But wait, there's more! Docker lets you deploy multiple distinct applications on the same machine, without worrying about configuration collisions. Our demo actually runs three “Hello world!” apps, in Ruby, Python, and Go. The only shared configuration we need to maintain is for HAProxy. $ h t t p - b l o c a l h o s t : 8 0 8 0 / r u b y p u t s ' H e l l o w o r l d ! ' $ h t t p - b l o c a l h o s t : 8 0 8 0 / p y t h o n p r i n t ( ' H e l l o w o r l d ! ' ) $ h t t p - b l o c a l h o s t : 8 0 8 0 / g o f m t . P r i n t l n ( " H e l l o w o r l d ! " ) 16 / 17
17. Further reading Containers & Docker: How Secure Are They? Docker breakout explot analysis Docker Container Breakout Proof-of-Concept Exploit Dockerfile Reference Docker Use Cases Docker User Guide Towards FutureOps: Stable, repeatable environments from dev to prod All images © 2014 Docker, Inc. 17 / 17