Docker

Docker

Docker builds are isolated with respect to 8 aspects:

• PID namespace - process identifiers and capabilities
• UTS namespace - host and domain name
• MNT namespace - file system access and structure
• IPC namespace - process communication over shared memory
• NET namespace - network access and structure
• USR namespace - user names and identifiers
• chroot() - controls the location of the filesystem root
• cgroups - resource protection

# List all docker images
docker images

# List all running containers
docker ps

# last run container
docker ps -l 

# Run container (with examples)
docker run [image:tag] /bin/echo 'Hello from your Docker container'
docker run -d ubuntu:latest /bin/bash -c "while true; do echo DOCKERMAN; sleep 1; done"
docker run -t -i [image:tag] /bin/bash
docker run -d -p 8080:80 tutum/apache-php

# Stop container execution
docker stop [containerid]

# View container logs
docker logs [containerid]

# Commit container to an image
docker commit [idofcontainer] [nameofnewimage]

# Remove an image
docker rmi [image-id]

# Remove container
docker rm [container-id]

Flags

-d - run container as daemon.

-t - TTY mode

-i - docker image

-p - port

Snapshots

changes in an image are not saved automatically, so you would have to commit the changes to a new or an existing image via docker commit command

Attach to a running container

docker run -t -i centos6:withapache /bin/bash
service httpd start
curl http://localhost:80
docker inspect [given-name-of-instance] | grep IPAddress | cut -d ":" -f2 | cut -d "\" -f2 = 1.2.3.4
docker attach [given-name]  //gives us the command prompt inside the container, already running instance
docker run centos6:withapache
docker ps

Nothing runs because the image does not have any bootup process by itself, starts/stops

The -d command runs the image as daemon

Removing images

if there are dependent images, you cannot remove the parent image, it will orphan the dependent images

Directory Structure

• /var/lib/docker

cat repositories-devicemapper | python -mjson.tool

reference file for repositories/images that exist

containers directory - containers that have yet to be committed and have dependencies on parent images

for any image in containers directory - cat config.json | python -mjson.tool

Startup services

• If you need to start a linux service like httpd on start, you have to add it to a bash startup script
• Edit .bashrc: /sbin/service httpd start
• After editing the file, the container needs to be committed

docker commit [container-instance] [container-name-new]
docker run -i -t -d centos:apacherunning /bin/bash

Pushing Images to Docker Hub

hub.docker.com - free account (1 private repo only)

docker push [image-name]

Adding External Content

To add content to a container, start an instance of an image then move files using SCP

In the Dockerfile, we can use the ADD command:

FROM redhat:centos6
MAINTAINTER Dmitriy Dubson <ddubson@example.com>

ADD testfile.html /var/www/html/testfile.html

Image Volume Management

Create a volume for any running container:

docker run -i -t -v /myapp test:html /bin/bash

-v = volume

We can create an empty directory on the local filesystem and mount that volume to the docker container

docker run -t -i -v /root/myvolume:/var/volume test:html /bin/bash

where myvolume is a folder on the local system

docker run -v /Users/<path>:/<container-path> ...

Advanced Network Management

• configuring a bridge adapter

   
ip link add r10 type bridge
ip addr add 10.10.100.1/24 dev br10- class C range (10.10.100)
ip link set br10 up

• configure docker to bridge:

docker.io -d -b br10 &

• run the image

docker run -t -i centos:centos6 /bin/bash

/etc/rc.local ->

auto lo
iface lo inet loopback

auto br0
iface br10 inet static
    address 10.10.100.1
    netmask 255.255.255.0
    bridge_ports dummy0
    bridge_stp off
    bridge_fd 0

Labs:

https://gist.github.com/ddubson/2217565de88de6d708d8

Interactive Shell Control

docker run -t -i —name MYCONTAINER <= name a container when running
docker exec -t -i MYCONTAINER /usr/bin/top <= attaching to a process in a container

Previous Container Management

docker ps -a => history of all containers that ever ran
docker ps -a | wc -l (count number of lines, number of containers that are stopped)

Delete everything that is 7 days ago

Docker ps -a | grep '7 days ago' | awk '{print $1}' | xargs docker rm

Container Routing

Set a static route

docker route add -net [ip] netmask 255.255.255.0 gw [gatewayip]

Sharing Container Resources

docker run -d -i -t -v /data --name DATA1 ubuntu:latest /bin/bash
docker run -d -i -t --volumes-from DATA1 --name DATA2 ubuntu:latest /bin/bash

Committing a running container

• Run an image: docker run -t -i ubuntu:latest /bin/bash
• Once in terminal, update apt-get and then install the cmd “htop”
• In another terminal, run docker ps and see what the container name is
• Via container name, run docker commit [name] [new-image-name]
• Run the new image: docker run -t -i ubuntu:htop /bin/bash

Check if cmd is there.

Useful Docker CLI Commands

• docker cp
  • Copy files from a container
  • e.g. docker cp [name-of-container]:/etc/yum.conf tmp
• docker diff
  • View all the changes of the container since it was started.
  • e.g. docker diff [name-of-container]
• docker events
  • A realtime view of events that Docker captures (e.g. start/stop a container)
  • e.g. docker events
  • e.g. docker events --since '2014-12-05'
• docker history
  • History of an image
  • e.g. docker history centos:latest
• docker exec
  • Send remote commands to a container
  • docker exec -I -t MyTestContainer1 /usr/bin/yum -y update
• docker info
  • information about running containers
  • e.g. docker -D info
• docker kill
  • kill a container immediately
  • sends kill -9
  • e.g. docker kill [container-name]
• docker save/export
  • docker [export|save] OurWeb3 > OurWeb.tar
  • builds base image from container into a tar file
• docker load/import
  • docker [load] < OurWeb.tar
  • docker load -i OurWeb.tar
  • imports an external image
• docker pause/unpause
  • pause the container execution (freeze it)
  • unpause the container execution (unfreeze execution)
• docker top
  • top command into a container

Optimizing Dockerfile Builds

docker images -t (can see all the layers of containers that were built by Dockerfile)