Working with Docker Containers

Install Docker Containers:

We can install Docker containers in two different ways, One is to install the same with the yum package manager directly or second method is we can use curl with the get.docker.com site. We will be using yum this time.

1.  Log into our machine as a user with sudo or root privileges.
2.  Make sure our server existing yum packages are up-to-date.

# yum update

3. Add the yum repo:

# vim /etc/yum.repos.d/docker.repo
[dockerrepo]
name=Docker Repository
baseurl=https://yum.dockerproject.org/repo/main/centos/7
enabled=1
gpgcheck=1
gpgkey=https://yum.dockerproject.org/gpg

Install the Docker package.

# yum install docker-engine

After, Docker package has been installed, start the daemon, check its status and enable it system wide using the below commands:

# systemctl start docker
# systemctl status docker
# systemctl enable docker

Verify docker is installed correctly by running a test image in a container.

# docker run hello-world

Unable to find image 'hello-world:latest' locally
    latest: Pulling from hello-world
    a8219747be10: Pull complete
    91c95931e552: Already exists
    hello-world:latest: The image you are pulling has been verified. Important: image verification is a tech preview feature and should not be relied on to provide security.
    Digest: sha256:aa03e5d0d5553b4c3473e89c8619cf79df368babd1.7.1cf5daeb82aab55838d
    Status: Downloaded newer image for hello-world:latest
    Hello from Docker.
    This message shows that your installation appears to be working correctly.

    To generate this message, Docker took the following steps:
     1. The Docker client contacted the Docker daemon.
     2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
            (Assuming it was not already locally available.)
     3. The Docker daemon created a new container from that image which runs the
            executable that produces the output you are currently reading.
     4. The Docker daemon streamed that output to the Docker client, which sent it
            to your terminal.

Now, you can run a few basic Docker commands to get info about Docker:

For system-wide information on Docker

# docker info
# docker version

4. In order to start and run a Docker container, first an image must be downloaded from Docker Hub on your host. Docker Hub offers a great deal of free images from its repositories.
To search for a Docker image, Ubuntu for instance, issue the following command:

# docker search ubuntu

5.  We want to run Ubuntu, So download it locally by running the below command

# docker pull ubuntu

6. To list all the available Docker images on your host issue the following command:

# docker images

7. In order to create and run a container, you need to run a command into a downloaded image, in this caseUbuntu, so a basic command would be to display the distribution version file inside the container using cat command, as in the following example:

# docker run ubuntu cat /etc/issue

8. To run one of the containers again with the command that was executed to create it, first you must get the container ID (or the name automatically generated by Docker) by issuing the below command, which displays a list of the running and stopped (non-running) containers:

# docker ps -l

9. Once the container ID has been obtained, you can start the container again with the command that was used to create it, by issuing the following command:

# docker start <Container ID>

10. In order to interactively connect into a container shell session, and run commands as you do on any other Linux session, issue the following command:

# docker run -it ubuntu bash

11. To quit and return to host from the running container session you must type exit command. The exit command terminates all the container processes and stops it.

# exit

12. To reconnect to the running container you need the container ID or name. Issue docker ps command to get the ID or name and, then, run docker attach command by specifying container ID or name, as illustrated in the image above:

# docker attach <container id>

 

Install Apache Web server in Docker container

Once I start the new docker container as describe earlier, I will start two new containers for my Apache and Mysql deployment

# docker start <Container ID>
# docker run -it ubuntu bash

Once you are in the Ubuntu docker container, install the apache packages

# apt-get update && apt-get install apache2

Now its time to start the service,

# /etc/init.d/apache2 start

To verify if the server is running, try using links command. (We might need to install it if thats not available.

# apt-get install links  (if links command is not installed)
# links http://127.0.0.1

To store the current state of the Docker containers, we need to commit them, so that they start with your configuration next time when you start them by 'exit' command.

# docker commit <container ID> yogesh/apache

Install MySQL server in Docker container

In other TAB, we can start one more Docker container for Mysql server

# apt-get update
# apt-get install mysql-server

(Type password when asked for Mysql database password)
After mysql is installed, start the service:

# /etc/init.d/mysql start

Try and test it out:

# mysql -u root -p

(Type password)
> show databases;
(Displays all default databases)
>exit

(To exit out of server)
Default Logs for mysql are saved in  /var/log/mysql/error.log
To store the current state of the Docker containers, we need to commit them, so that they start with your configuration next time when you start them after the 'exit'.

# docker commit <container ID> yogesh/mysql

You can view the complete procedure in below video: