What is Docker Container?
Docker is an open-source engine that automates the deployment of any application as a lightweight, portable, self-sufficient container that will run virtually anywhere.
Docker containers can encapsulate any payload, and will run consistently on and between virtually any server. The same container that a developer buildsand tests on a laptop will run at scale, in production*, on VMs, bare-metal servers, OpenStack clusters, public instances, or combinations of the above.
[Source: As in package description, Vendor: Fedora Project]
Difference between Docker and VM [Pic source, Internet ]
Let's try out few basic stuff using Docker (Tested on a CentOS-6x based VM);
1. Install epel repo to get Docker-io
[root@docker-vm ~]# yum install epel-release -y
2. Install docker-io package and start the service;
[root@docker-vm ~]# yum install docker-io -y
[root@docker-vm ~]# service docker start
Starting cgconfig service: [ OK ]
Starting docker: [ OK ]
3. List if we have any Docker image avaialble locally;
[root@docker-vm ~]# docker images
REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE
4. Since images are not available locally, I would pull a CentOS-6.9 image and try out few things;
Pulling a specific Centos docker image version;
[root@docker-vm ~]# docker pull centos:6.9
6.9: Pulling from centos
055b9989266a: Pull complete
f1070d829305: Pull complete
e071bce628ba: Pull complete
Digest: sha256:e7bdc458659b6e644ae85694f2baaf3727c06ad82186fca80f4e3a8e88907cc3
Status: Downloaded newer image for centos:6.9
5. List images once more;
[root@docker-vm ~]# docker images
REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE8.
centos 6.9 e071bce628ba 5 weeks ago 194.7 MB
6. Now run our first container [docker run -it stands for docker run --interactive --tty, do a man docker-run for options] ;
[root@docker-vm ~]# docker run -it e071bce628ba /bin/bash
[root@bd93eb2b1ccf /]#
["e071bce628ba" is the IMAGE ID]
7. Now, within our container, let's install few packages [eg. iproute, httpd, nmap etc.];
[root@bd93eb2b1ccf /]# yum install iproute nmap httpd -y
8. Start HTTPD ;
[root@bd93eb2b1ccf /]# service httpd start
Starting httpd: httpd: Could not reliably determine the server's fully qualified domain name, using 172.17.0.1 for ServerName [ OK ]
9. Open a new terminal on the Host system and check what containers are running;
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
bd93eb2b1ccf e071bce628ba "/bin/bash" 17 minutes ago Up 17 minutes prickly_tesla
So, we have one running container from previous steps;
10. Detach and attach from/to an Docker container;
A. Detach from a container;
Press Ctrl-P + Ctrl-Q to detach from the container;
[root@docker-vm ~]# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
bd93eb2b1ccf e071bce628ba "/bin/bash" 24 minutes ago Up 24 minutes prickly_tesla
B. Once detached, you can again connect to the running container. You need to provide the "CONTAINER ID" to attach to the reqd container;
[root@docker-vm ~]# docker attach bd93eb2b1ccf
[root@bd93eb2b1ccf /]#
11. Now, we will save our custom image with a different name [I named it as "centos6.9-httpd-bijit"] with all our custom packages (remember we installed iproute, httpd, nmap etc)
Detach yourself [ctrl-p + ctrl-q] from the running container and save the container as new
Docker image;
[root@docker-vm ~]# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
bd93eb2b1ccf e071bce628ba "/bin/bash" 36 minutes ago Up 36 minutes prickly_tesla
[root@docker-vm ~]# docker commit bd93eb2b1ccf centos6.9-httpd-bijit
=================================
[root@docker-vm ~]# docker commit bd93eb2b1ccf centos6.9-httpd-bijit
dc988142a75d3f7d2308543223e987be89e31da7d6f579109f0f2bb4ee0c192a
[root@docker-vm ~]# docker images
REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE
centos6.9-httpd-bijit latest dc988142a75d 48 seconds ago 320.7 MB
centos 6.9 e071bce628ba 5 weeks ago 194.7 MB
=================================
12. Run a container using the newly built image;
[root@docker-vm ~]# docker run -it centos6.9-httpd-bijit /bin/bash
[root@29c8a4bd34d1 /]# service httpd start
So, we have successfully ran a container using our custom Docker image.
13. Let's stop our container from previous step (ctrl+d from within container would do the job, [ docker stop
14. Now, we will Publish the container port (80 in our case) and map that to the Host OS, also provide a custom name for the container that we are going to start;
[root@docker-vm ~]# docker run -it -p 172.16.20.4:80:80 --name tux-container centos6.9-httpd-bijit /bin/bash
[root@a3923d777eaf /]#
[root@a3923d777eaf /]# service httpd start
Starting httpd: httpd: Could not reliably determine the server's fully qualified domain name, using 172.17.0.4 for ServerName
15. Now, try accessing Apache page using the Host IP address http://172.16.20.4/
[Remember our container IP is 172.17.0.4 while Host IP is 172.16.20.4 We are running HTTPD within the container and NOT on the Host systems]
============================================
List of basic commands;
============================================
Pushing an image to Docker Hub
A. Detach from an running Docker container and note down the container
id;
# docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
3a8a3576695d e071bce628ba "/bin/bash" 11 minutes ago Up 11 minutes tender_goldstine
B. Commit the changes using the following syntax;
docker commit
eg. in our case;
# docker commit 3a8a3576695d bijit/tuxb:centos6.9-httpd-bijit
4ff826f5c36ec9b6c452443ea1d759675456f53470fc30ea201b2be363e97627
C. Now push this repository to the registry designated by its name or tag;
Syntax: docker push
eg.
====================
# docker push bijit/tuxb:centos6.9-httpd-bijit
The push refers to a repository [bijit/tuxb] (len: 1)
4ff826f5c36e: Image push failed
Please login prior to push:
Username: bijit
Password:
Email: xxxxxx@gmail.com
WARNING: login credentials saved in /root/.docker/config.json
Login Succeeded
The push refers to a repository [bijit/tuxb] (len: 1)
4ff826f5c36e: Image already exists
e071bce628ba: Image successfully pushed
f1070d829305: Image already exists
055b9989266a: Image successfully pushed
Digest: sha256:cce65ad4fc75b136f84b567ae3f281de2723115e13d21efa63660b36fbe53e42
====================
How to Pull the private Docker image?
1. Login to Docker Hub from command line.
docker login --username=yourhubusername --email=youremail@company.com
====================
[root@ins-2 ~]# docker login --username=bijit --email=xxxxx@gmail.com
Password:
WARNING: login credentials saved in /root/.docker/config.json
Login Succeeded
====================
2. Pull the image which was pushed to that private repository.
#docker pull bijit/tuxb:centos6.9-httpd-bijit
====================
[root@ins-2 ~]# docker pull bijit/tuxb:centos6.9-httpd-bijit
centos6.9-httpd-bijit: Pulling from bijit/tuxb
055b9989266a: Pull complete
f1070d829305: Pull complete
e071bce628ba: Pull complete
4ff826f5c36e: Already exists
Digest: sha256:cce65ad4fc75b136f84b567ae3f281de2723115e13d21efa63660b36fbe53e42
Status: Downloaded newer image for bijit/tuxb:centos6.9-httpd-bijit
====================
3. List the images available locally now;
# docker images
REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE
bijit/tuxb centos6.9-httpd-bijit 4ff826f5c36e 10 hours ago 326.5 MB
4. Run a container using the image dowloaded from Private repository;
# docker run -it 4ff826f5c36e /bin/bash
[root@29c3296b8e48 /]#
["4ff826f5c36e" is the IMAGE ID ]
5. To stop the container either [ctrl+d] from within container or docker stop
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