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Build Docker Image From A Running Container

In this lab session we are going to build the image from running container and for that we are going to use nginx image and run the image next we are going to modify the web contents and build the new nginx image with modify contents.

Step 1 - Run the nginx container

Search the nginx offical image

docker search nginx

Pull the nginx image

docker pull nginx

Run the nginx container

  • -p 8080:80 option -- tells docker to pass connections from your server’s HTTP port to the containers internal port 80.
  • -d -- makes the container run on background
docker run --name containerA -p 8080:80 -d nginx:latest

List running docker processes

docker ps

Step 2 - Check the web site is working or not

Check that weather our website (which is hosted with nginx on docker container) is working or not for this we use the wget command who request our web page and download the index.html from our container.

wget http://localhost:8080

If you get index.html file then it is working .
If you don't have wget command in your system then you can install it by below command.

apt-get install -y wget

To see the contents of index.html file

cat index.html

After that remove index.html file

rm index.html

Step 3 - Modify the contents of web page

Now in this step we want to modify the content webpage
So first we want to get the access of bash of our running container

  • exec -- it is use to Run a command in a running container
  • -it -- the -i (interactive) flag to keep stdin open and -t to allocate a terminal.
  • containerA -- it your nginx running container name .
  • /bin/bash -- it is a command which you want to execute .
docker exec -it containerA /bin/bash

When you get the running container terminal execute following command

echo 'hello this for testing' > /usr/share/nginx/html/index.html
exit

Step 4 - Check weather modify contents are display or not

Now in this step we can check weather we get our modify content or not

wget http://localhost:8080

To see the contents of index.html file

cat index.html

If you get hello this for testing then it working fine .
After that remove index.html file

rm index.html

Step 5 - Create the image from running container

In This step we want to create image of our nginx running container

  • commit -- Create a new image from a container's changes
  • containerA -- it is name of our running nginx container
  • nginx_modify:1 -- it name of your new image and tag
docker commit containerA nginx_modify:1

To check that weather your new image is created or not

docker images

Step 6 - Stop and remove all containers

Now it time to stop your all running containers and so we get all port free

  • stop -- is use to stop the running container with that we provide the container name
  • rm -- is use to remove the container with that we provide the container name
docker stop containerA
docker rm containerA

Step 7 - Run new container with newly created image

In this step we are going to start new container with our new nginx image

docker run --name containerB -p 8080:80 -d nginx_modify:1

Step 8 - Check that weather our modify contents are display or not

And Finally we are going test the weather our new image is show in modify contents or not

wget http://localhost:8080

To see the contents of index.html file

cat index.html

If you get hello this for testing then we did it.