Docker

currently with docker you are limited to only linux machines and apps. It is like installing various zip files on your os.

because of the use of base image we can save space.All the containers use the same base image. If you want 100 containers in traditional vm env you would have needed 100GB space considering 1gb per image but with docker you will need only 1gb of space. Suppose if you need emacs and apache then docker will add to separate images for it on top of each other and with the base image it will form a union image. this image is readonly so to write in it docker will place a writable container and the whole set container:image(apache)+image(emacs)+base image will make a whole container in the docker.  But the writable container is not persistent. Docker boots the image/ image layers on top f each other.

apt-cache search docker.io ---will display a list of packages containing docker

apt-chache show docker.io ---- will display all details of packaage

Check if it is latest version.

Docker guys have provided us with a script get.docker.com. it has the script for installation.

This is to be executed .

wget -qO- https://get.docker.com/ | sh to install docker latest.

If you want to add non root user in docker then execute the following command:

sudo usermod -aG docker your-user

check by id your-user to check in which group  user is present it should be present in docker group.

all images are present in registry. docker own registry at docker hub. first you will need to pull the docker images from the registry with docker pull command. After that you can use docker run. If you have specified which images to use then docker will automatically pull the images from registry while docker run is executed. the registry of docker is hub.docker.com

You can search using docker search mysql

to download use docker pull ubuntu

always pull the latest you can also use docker pull ubuntu:latest it is same. :latest is called image tag or the container tag. you can pull using version as well: docker pull ubuntu:14.04

To check what images you have you can issue the docker images command

To start a container use

docker run -ti ubuntu:14.04 /bin/bash -t for terminal i for interactive

to quit container without stopping it press CTRL+P+Q

to check which docker containers are running then command docker ps

to attach to running container use command docker attach <container id>/<container name>

To exit docker and stop the container as well press CTRL+D

To list all the containers even the which that are not running use command docker ps -a

If you exit with ctrl + d and want to start the container again then you can use the command docker start <container-name> 

This will start container in the background

To display docker processes use command docker top / docker top <container-name>

to stop use docker stop <container-name>

in /var/lib there is a folder docker. in that you will have folder container in that you can see folders of running containers with their long ids. In that folders you can see the following files:

<id>-json.log, hosts, config.json, resolv.json, hostconfig.json, resolv.conf.hash, hostname.

In hostname file you will have the short id of container which is shorter version of the long id.

you can also run docker run -ti ubuntu:12.04 /bin/bash it will download automatically.

If you dont want to immediately attach to the container then you can run docker in detached mode:

docker run -d -ti ubuntu:14.04 --name=duck /bin/bash

-d for detached

-ti also because if you dont give you wont be able to login into it.

But it is not persistant if you want the docker container to be persistent then you can use the command:

docker run -ti -v /data --name=duck2 ubuntu:14.04 /bin/bash

-v for volume you have to give it a mount point it will create this mount point inside the container folder.

name should not be same as previous

When in bash inside the container goto /dataand then start working and creat files.

then after quiting the container with ctrl+p+q then in your local machine goto /var/lib/volumes/<container-long-id>/_data you can find all your files here.

If you remove from inside container it will be removed from local machine as well

If you want to attach local directory to continer then

docker run -ti -v /srv/duck3:/data --name=duck3 ubuntu:14.04 /bin/bash

/srv/duck3 local dir

/data container dir

docker run -d -p 3306 -ti mysql /bin/bash

-p for port

this will open port 3306 and nat it to external port.

you check by this command locally iptables -L -t nat

-L list

-t for table nat

it will nat to random port if want to pen specific port

docker run -d -ti -p 3306:3306 mysql /bin/bash

you can also specify the specific ip address if you want with -p <ip>:3306:3306

if you and your friend have vm and want to sync up you may have to transfer 20gb of file. but with docker docker diff to check the difference then docker commit then docker push which will only be the change.

docker containers: are actual containers running the applications and includes os, user added files, and meta data

docker images: helps to launch docker containers

docker file: is a file containing instructions that help automate image creation

layer: each file system that is stacked when docker mounts rootfs.

Install docker using:

sudo rpm install docker

docker commands:

docker pull: pull a pre-built image from public repos

docker run: run in 3 modes background,foreground,interactive

docker logs: logs of running logs

docker commit: save container state

docker images: list of all images

docker diff: changes in files and directories

docker build: build docker images from

dockerfiles

docker inspect: low level info about containers

docker attach: interact with running container

docker kill: kill a container

it is beneficial to separate every server like in lamp have separate php, mysql,apache in diff containers

you can use a supervisor -n to it

docker file:

automates image creation process

set of instruction to create an image

syntax: instruction argument

how docker files different:

dockerfiles run in layers

after every command a new layer is created.

if there is a mistake in line 29 of 30 if you corect in docker then first 28 skip because already run and just resolving the issue.

Dockerfile commands:

MAINTAINER <author name> sets autho name

RUN <command> execute command

ADD <src><dest> copy files from one location to another

from local machine to inside docker

CMD["executable","param1","param2"] provides default for executing container

EXPOSE <port>port on which container might get deprecated

ENTRYPOINT ["executable","param1"...] configure container as exe from where you want to start execution

WORKDIR /path set working dir

ENV <key> <value> set env variables

USER <uid> set UID for use when running an image

VOLUME ["/data"] enable access to a directory from a working container mount from host to docker

docker create   -----using dockerfile

Layering issue with dockerfile is that docker is restarted after every command you will losse any environment variable

If you want to run a if then you will have to write it on a single line.

you can override this in command line

if container when you execute CMD  and command as main command and if that command quits or goes in background.

boot2docker to bootstrap instead of chef