Docker Deep Dive

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Course Introduction

The Basics

By scmGalaxy.com

About Me

DevOps@RajeshKumar.XYZ

What We’ll Learn

• Linux Containers
  • Containers vs Virtual Machines << FIGHT!!
  • Kernel namespaces, cgroups, Capabilities…
• Docker Engine
  • Execution Driver: libcontainer vs LXC
  • AUFS, OverlayFS, Device Mapper…
• Docker Images
  • docker build | docker images | docker inspect…
  • Union mounts, Layering, Dockerfile
• Docker Containers
  • docker start | stop | restart
• Registries, Volumes, Networking….

Prerequisites

Introducing Containers

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It’s all about applications

server : application:

1 : 1

Physical Machine

Containers are more lightweight than Virtual Machines

Physical Machine

Containers consume less CPU, RAM and disk resource than Virtual Machines

Kernel Namespaces

Control Groups (cgroups)

Capabilities

The Evolving Docker Platform

The Future of Docker

Physical Machine

Chip-level assists for Containers

• Performance offloads
• Security features
• ......

Coming up Next….

• Installing Ubuntu and CentOS Linux
• Installing and updating the Docker Daemon

Installing Ubuntu Linux and CentOS Linux

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Installing and Updating Docker

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Module Recap

Major Docker Components

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Module Outline

• Docker Engine
• Images
• Containers
• Registries and Repositories

Major Docker Components

The Big Picture

Containers can contain malicious code

Trust the code you run!

Registries and Repositories

A Quick Look

Module Recap

A Closer Look at Images and Containers

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A Closer Look at Images and Containers

The Good Stuff!

Focusing in on Containers

More Good Stuff…

One Process per Container…

Usually…

Module Recap

Container Management

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Module Outline

• Container Management
• Container Config
• Look Inside Running Containers
• Different Ways to Get Shell Access

“One process per Container”

We can run multiple processes per Container

“One process per Container”

• One concern per container
• Lean
• Simple!

We can run multiple processes per Container

docker attach

• Attaches to PID 1 inside the container
• In the real world, PID 1 inside a container will probably not be a shell

ssh

• Most containers won’t be running an SSH server

nsenter

• Allows us to enter Namespaces
• Requires the containers PID (get from “docker inspect”)

Module Recap

Building from a Dockerfile

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Module Outline

• The Big Picture
• Dockerfile Basics
• Creating a Dockerfile
• Building from a Dockerfile

• Dockerfile
• Plain-text
• Simple format
• Instructions to build image

Module Recap

Diving Deeper with Dockerfile

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Module Outline

• The Build Cache
• Dockerfile and Layers
• Dockerfile Instructions
  • CMD, ENTRYPOINT, ENV, VOLUME

• Dockerfile
• Plain-text
• Simple format
• Instructions to build image

 
	CMD                                              RUN
	Run-time                                         Build-time
	Run commands in
	containers at launch time                        Add layers to images
	                                                 Used to install apps
	Equivalent of -
	    docker run < args > 
	    docker run < args > /bin/bash
	One per Dockerfile
	
	
	                        

 
    Shell Form                                     Exec Form
    Commands are expressed the same                JSON array style -
    way as shell commands                            [“command”,“arg1”]
    Commands get prepended                         Containers don’t need a shell
    by “/bin/sh –c”                                Avoids string munging by the shell
    Variable expansion etc…                        No shell features –
	                                               No variable expansion
                                                        No special characters (&&,||,>….)

	                        

ENTRYPOINT

• Can’t be overridden at run-time with normal commands – docker run …< command >
• Any command at run-time is used as an argument to ENTRYPOINT
• Variable expansion etc…

Module Recap

Docker Networking

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Module Outline

• The “docker0” Virtual Bridge
• Virtual Ethernet Interfaces
• Exposing Ports
• Linking Containers

Module Recap

Troubleshooting

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What We’ll Learn

• Docker Daemon Logging
• Container Logging
• Troubleshooting Images
• Network Troubleshooting

Docker Daemon Logging

Container Logging

Replay

Use volumes to share and
persist data

Image Troubleshooting

Test Before Dockerfile

         FROM ubuntu:15.04

 
					FROM ubuntu:15.04
						
					
					
					CMD ping 8.8.8.8

 
					FROM ubuntu:15.04
					
					
					RUN apt-get install–y
					iputils-ping
							
					CMD ping 8.8.8.8

 
					FROM ubuntu:15.04
					
					RUN apt-get update
					
					RUN apt-get install–y
					iputils-ping
						
					CMD ping 8.8.8.8

 
					FROM ubuntu:15.04
					
					RUN apt-get update &&\
					  apt-get install –y \
					  iputils-ping
						
					CMD ping 8.8.8.8

Image Troubleshooting

Intermediate Images

Network Troubleshooting

docker0

Network Troubleshooting

IPTables

- - icc =

- - iptables =

*Both default to true

Module Recap

Lightning Fast Recap

Next Steps

This isn’t the end.

It’s…. just the beginning!

Questions?

Thanks for You

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