As we all know containers are ephemeral in nature and it does not persist the data. If container is removed the data is gone along with it. So per fix this issue, we can attached a persistent storage with container. To do the same, we configure a folder on host file system to be attached to container for persistent storage.
we will start will creating a folder on host system.
We will also need to take care of SElinux labeling, so we will setup a rule for '/var/local/mysql' folder and anything underneath. So once rule is set run restorecon to change label.
After the selinux labeling is setup we will also have to take care of file system permission, so that container to write on the filesystem of host. Since we are taking example of Mysql process, we will change ownership to mysql uid and gid for the folder.
Now we are all set to run a container. So we will have to pull the image. You might need to login to the registry if needed.
Now we have the image fetached, lets run the container with the storage mount of '/var/local/mysql' folder of host to container folder of '/var/lib/mysql/data'.
-d = Running container in background
-v = Bind a volume
-e = Environmental variable
After running the container, you will find bunch of files created underneath the /var/local/mysql folder. Also you might notice that the files are owned by Mysql uid and gid.
Now, we will access the shell of the container to access the mysql process.
We can access the database we created called 'projectmanhattan' and we will create the database with a table called 'newyork'.
One table is created under the database, lets populate it with some data to test the data persistence of storage.
Now we will delete the old container named 'mydb1' and create another container named 'mydb2' with same properties and mounting the same volume to verify if data persisted or not. We can see that data still exists even after deleting the initial container.
Conclusion:
We are able to persist the data if we mount the host file system storage in the container.
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:
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
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:
