Docker Quick Start

In this post we will learn how to quickly start using docker


1. Install Dockers on Ubuntu 16.04 or above


Update the Repository

$ sudo apt-get update
$ sudo apt-get install \
apt-transport-https \
ca-certificates \
curl \
software-properties-common

Download the GPG key from the docker site

$ curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -

Add docker repository

$ sudo add-apt-repository \
"deb [arch=amd64] https://download.docker.com/linux/ubuntu \
 $(lsb_release -cs) \
  stable edge test"

Update the packages and install docker community edition

$ sudo apt-get update
$ sudo apt-get install docker-ce

Foo

Finally check the docker installation is correct

$ sudo docker run hello-world

You can check status, on, off and restart docker using following commands

$ sudo service docker status
$ sudo service docker start
$ sudo service docker stop
$ sudo service docker restart

To run the docker without sudo commands

$ sudo usermod -aG docker $USER

Logout and then check with following command

$ docker ps -a
$ docker ps
## Docker Hub

2.Docker Hub


Signup to https://hub.docker.com/

one private repository for free and unlimited public repository

Explore Following on https://hub.docker.com/

  Explore Official Repositories
 https://hub.docker.com/explore/
  - Explore Mysql official repository
  - Docker Pull Command Syntax and how to use this image
  - Search for wordpress and how to use this image
  - Click on the docker files link which is redirected ot github and check how the wordpress image is built

3. Base Images


Check for the availabe images

$ docker images

Search for Docker

$ docker search ubuntu
$ docker search apache
$ docker search cartoview
$ docker search mysql
$ docker search httpd

Examine the output

Lets use Docker pull command to get image

Docker will pull the latest version of image

$ docker pull hello-world

Check the image using docker images command

$ docker images

Run the docker using docker run command, Its always good to specify the tag

$ docker run hello-world:latest

You can also run the docker image using its ID which you can get from the docker images output

$ docker run f2a91732366c

Lets pull some useful image from hub

$ docker images

All below command get the same image

$ docker pull centos:centos7
$ docker pull centos:latest
$ docker pull centos

Following will pull the centos6 image

$ docker pull centos:centos6

Lets pull some of the ubuntu images, Below command will pull ubuntu 16.04

$ docker pull ubuntu:latest

Below command will pull ubuntu 17.10

$ docker pull ubuntu:artful

Lets pull nginx

$ docker pull nginx:latest

Getting information from the docker

$ docker inspect nginx:latest
$ docker inspect ubuntu:artful
$ docker inspect centos:centos7

You can also give the ID for inspection

$ docker inspect 275d79972a86

Observe the details given in the output

Running Container

We have lots of base images

$ docker images
$ docker run hello-world

Lets pull docker/whalesay image which is built for study of docker

$ docker search docker-whale
$ docker pull docker/whalesay
$ docker run docker/whalesay cowsay hello
$ docker run docker/whalesay cowsay I AM DOCKER

This container has cowsay application which displays hello

How to know what all containers are running on our system

$ docker ps

Why output is nothing ? Containers run and stop.

Get the list of containers which are stopped and I have run

  $ docker ps -a

  - Each container has unique ID
  - Command shows what executed when it started
  - NAMEs which are used to refer

  $ docker inspect hungry_booth

              If docker is running then you can see ip address etc.

Docker Network Interface

  $ ifconfig
      docker0:
      flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
      inet 172.17.0.1  netmask 255.255.0.0  broadcast 172.17.255.255
      inet6 fe80::42:b7ff:fee2:978e  prefixlen 64  scopeid 0x20<link>
      ether 02:42:b7:e2:97:8e  txqueuelen 0  (Ethernet)
      RX packets 0  bytes 0 (0.0 B)
      RX errors 0  dropped 0  overruns 0  frame 0
      TX packets 55  bytes 4903 (4.9 KB)
      TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

      See the range of ip address which docker is going to assign to containers when they are running

      **We are not going to see how to configure the network of the docker interfaces**

Lets start container and then inspect

$ docker run -it centos:latest /bin/bash
                    - run : run the container
                    - i   : interactively
                    - t   : connect it to terminal or tty
                    - run centos latest
                    - run /bin/bash command

  Run following command in the container

  $ whoami

  Now open another terminal and run following command It will show you the container is running

  $ docker ps
  $ docker inspect goofy_easley

  To come out of the centos container

  [root@d0756568442e /]# exit

  Exit terminate the container, now you can chech following command

  $ docker ps
  $ docker ps -a

 Why it existed ? Its because the command we run is now terminiated so container

To run container in the backgroud use -d option

    $ docker run -d centos:latest /bin/bash

    Here command executed and finished

Lets run the nginx in the background mode

    $ docker run -d nginx:latest
    $ docker ps

Now here the container is running in the backgroud. It continues to run.

Now Lets inspect and find the ip address of the container which is running

    $ docker inspect focused_swirles
    $ ping 172.17.0.2

We are able to ping because the container is running

    $ docker ps
    also tell us that nginx has port 80

    So open the browser and put 172.17.0.2 you can also use elinks terminal based browaser to check the nginx webpage

    You can install elinks as follows

    $ sudo apt install elinks
    $ elinks http://172.17.0.2

    Use q to exit

To stop nginx container

    $ docker stop focused_swirles

To start docker with name, start 2nd instance of nginx image

    $ docker run -d --name=MyWeb1 nginx:latest
    $ docker ps

    $ docker inspect MyWeb1
    $ docker stop MyWeb1

Ip address is from dhcp of docker interface, we we run another container it will get next ip from ip pool.

To start container again

    $ docker container start MyWeb1

Container Lifecycle

Lets have a look at all images we have

$ docker images

Lets see whether we are running any Container

$ docker ps

Lets see history of the Containers we run

$ docker ps -a

Lifecycle of Container

$ docker run -d --name=LifeCycle1 nginx:latest
$ docker ps
$ ping 172.17.0.2

Container is running, its ip must be 172.17.0.2

Attach to the Container

$docker attach Lifecycle1

You are attached to the process and not the coommand prompt

Now if you put CTL + C then you will close the Container

$ docker ps

Restart Container

$ docker restart Lifecycle1
$ docker start Lifecycle1
$ docker ps

Run command in the Container with out affecting the Container process

$ docker exec -it LifeCycle1 /bin/bash
                        - exec execute command
                        - -i interactively
                        - attach to the tty / terminal
                        - execute the /bin/bash command in the container

  Now from here if you exit, container will not exit. It will continue to run

  You have just executed and not attached. If you have attached then it would exit.

Docker Stop

  $ docker stop LifeCycle1

Docker Restart or start

$ docker restart LifeCycle1
$ docker ps

  ## Image and Container Management

  ### How to deal with images and containers

$ docker images

### Delete image which is not used
    $ docker rmi centos:centos6

### Delete the image which is being used
    $ docker rmi hello-world

    This must give error, you can force but its better to first delete the Container

    $ docker rm Container-Name
    $ docker rm Container-ID Container-ID
    $ docker rm fd61930cb2b9

    By force you can delete image
    $ docker rmi -f hello-world

If you remove images, you will be able to run the containers

To stop all non-running Container delete

    $ docker ps -a -q
    $ docker rm `docker ps -a -q`

Redirection - Ports and Volumes

Lets see which all images we have available

$ docker images

Lets run the ngins container

$ docker run -d nginx:latest

To check the Ip address

$ docker inspect stupefied_ramanujan | grep IPAddr

Check the nginx is running using the elinks

$elinks 172.17.0.2
$elinks localhost

Here container will show the web page but the localhost will not.

How to redirect from local port to container ?

Lets stop the container

  $ docker stop stupefied_ramanujan

and also lets remove the container

  $ docker rm `docker ps -a -q`

Above will remove all containers

Port redirection

  $ docker images
  $ docker run -d --name=WebServer2 -P nginx:latest

-P makes forawarding 32768 to 65000 range

Now You can connect to the container with two ways but lets see the port it is picked for binding

  $ docker ps

In my case port 32768 is picked upby container

$ docker inspect WebServer2

IP address of container is 172.17.0.2

$ elinks 172.17.0.2 $ elinks http://localhost:32768

You will be able to connecct to nginx using both the ways shown above

To know which port is redirected you can also use follwing command

$ docker port WebServer2 $CONTAINERPORT

To run bind a specific port like following 8090 we use -p option

$ docker run -d -p 8090:80 --name=MyWebServer3 nginx:latest

$ docker ps

Check port which is getting redirected

You can check forwarding using follwing commands

  $ elinks 172.17.0.2
  $ elinks http://localhost:8090

Mounting Volumes

  $ mkdir www
  $ cd www
  $ vi index.html

Put following code in the index.html My Custom HTML

    $ docker run -d -p 8070:80 --name=WebServer5 -v /home/tayyabali/www:/usr/share/nginx/html nginx:latest

Now you can check the site in the localhost or using ip address of the container as follows Check Ip

    $ docker ps
    $ docker inspect
    $ elinks 172.17.0.3
    $ elinks http://localhost:8070
    ## Docker File

    $ docker images
    $ docker ps

Stop containers if any running

    $ docker stop CONTAINER_ID/NAME

Lets Cleanup all the containers and keep only images

    $ docker ps -a
    $ docker rm `docker ps -a -q`
    $ docker ps -a
    $ docker ps

Lets build a directory for our build

    $ mkdir build
    $ cd build
    $ docker images

We only now have images

Create a file in build directory $ vi Dockerfile

Put followig text in the Dockerfile

    FROM debian:stable
    MAINTAINER tayyabali <tayyabsayyad@gmail.com>
    RUN apt-get update
    RUN apt-get upgrade
    RUN apt-get install telnet

Then lets build the image using followig command

  $ build$ docker build -t tayyabali/myapache .

You may see this is failed because of the questions it asks

  Do you want to continue? [Y/n] Abort

If build is failed you have only latest debian image available as you can see

  $ docker images

But what happens if we try to pur a unknow command in the file as shown below and build image

  FROM debian:stable
  MAINTAINER tayyabali <tayyabsayyad@gmail.com>
  RUN apt-get update
  RUN apt-get upgrade
  RUN apt-get install telnet
  RUN my-command

Docker uses cache memory for the image layer, When you run commands separately image layers are increased good to combine command together as following

  FROM debian:stable
  MAINTAINER tayyabali <tayyabsayyad@gmail.com>
  RUN apt-get update && apt-get upgrade -y && apt-get install -y telnet apache2 elinks openssh-server

Check the build image

  $ docker images

Lets add environment variables and file looks as followig

  FROM debian:stable
  MAINTAINER tayyabali <tayyabsayyad@gmail.com>

  RUN apt-get update && apt-get upgrade -y && apt-get install -y telnet apache2 elinks openssh-server

  ENV MYVALUE my-value

and build image again

  $ docker build -t tayyabali/myapache .

                It will build quickly becaue it used cache

Lets make container from the image

  $ docker run -it tayyabali/myapache:latest /bin/bash

and check the environment variable in container, you can see the value

  $ root@3012264990e9:/# echo $MYVALUE
  my-value

This is the way how you can pass variable in the container which is instantiated Lets Clean up again

    $ docker ps -a
    $ docker rm `docker ps -a -q`
    $ docker ps -a
    $ docker ps

Lets change the Dockerfile as follows to expose the ports

    FROM debian:stable
    MAINTAINER tayyabali <tayyabsayyad@gmail.com>

    RUN apt-get update && apt-get upgrade -y && apt-get install -y telnet apache2 elinks openssh-server

    ENV MYVALUE my-value

    EXPOSE 80
    EXPOSE 22

and build the image again

    $ docker build -t tayyabali/myapache .

Lets create the continer based on the image created

    $ docker run -it tayyabali/myapache:latest /bin/bash

Open New Terminal and see ports are now open

    $ docker ps

Exit from the container and remove the container

    $ docker ps -a
    $ docker rm `docker ps -a -q`
    $ docker ps -a
    $ docker ps

Starting apache in the container

Remove the port 22 we dont need that to be exposed and add command to start apache as follows

    FROM debian:stable
    MAINTAINER tayyabali <tayyabsayyad@gmail.com>

    RUN apt-get update && apt-get upgrade -y && apt-get install -y telnet apache2 elinks openssh-server

    ENV MYVALUE my-value

    EXPOSE 80

    CMD ["/usr/sbin/apache2ctl","-D","FOREGROUND"]

Build the image again

  $ docker build -t tayyabali/myapache .

Now once image is built make container as follows, we will run in the -d mode as we have executed commands in the continer

  $ docker run -d tayyabali/myapache:latest
  $ docker ps
  $ docker inspect CONTAINER_ID

Now check the apache page

$ elinks 172.17.0.2

Now you can do port redirection, valume management

You can also connect to the container as follows

$ docker exec -it fervent_visvesvaraya /bin/bash
root@c4ecaf1aa2fe:/# ps aux | grep apache
root@c4ecaf1aa2fe:/# echo $MYVALUE

See apache is running and MYVALUE is also set

Exit and check ps it will be still running

root@c4ecaf1aa2fe:/# exit
$ docker ps

To learn more about the docker files check the official repositories images docker files.