Docker allows you to build containers using a Dockerfile. Docker can build images automatically by reading the instructions from a Dockerfile. A Dockerfile is a text document that contains all the commands a user could call on the command line to build an image.
A Dockerfile consists of various commands and arguments listed successively to automatically perform actions on a base image in order to create a new one. It helps us to avoid issuing the command everytime while running container.
You can build the Docker image using one of the following two options:
- Interactively launch a BASH shell under the Ubuntu Base image, install Apache and its dependencies, and then save the image.
- Build the Docker image using Dockerfile with the web site included.
In this tutorial, I will explain how to create a Dockerfile, install the required Apache packages, add the necessary content and then build image.
Ubuntu Server 14.04 with Docker installed on your system.
Creating a Dockerfile
A Dockerfile is a text file that has a series of instructions to build an image. It supports a set of commands that we need to use in our Dockerfile.
There are several commands supported like FROM, CMD, ENTRYPOINT, VOLUME, ENV and many more. Each and every instruction set in the Dockerfile adds an additional layer to the image and then performs a commit.
Here, we will create a Dockerfile to create an image to install the Apache Web Server container.
To do this, we will need to create a file named Dockerfile using any text editor:
sudo nano Dockerfile
Add the following content which includes the commands and arguments for the Apache Web Server Container.
#Pull base image FROM ubuntu #Install Apache RUN apt-get update -y && apt-get install apache2 apache2-utils -y
#Define default port EXPOSE 80 ENTRYPOINT [ "/usr/sbin/apache2ctl" ]
#Define default command CMD [ "-D", "FOREGROUND" ]
Now, save and close the file.
In the above Dockerfile, the first parameter
FROM tells Docker what the source of our image is, in this example we're using Ubuntu image.
RUN parameter executes a series of commands inside the image to install package. Here we are updating the Ubuntu repository and installing Apache and other dependencies.
EXPOSE parameter set's the default Apache port
80 so that the website will be available normally. Then, the
ENTRYPOINT is set to /usr/sbin/apache2ctl so that the Apache Server will execute.
Building an Image using Dockerfile
Now, after we finish creating our Dockerfile for the Apache container, we are ready to create our first Apache Web Server images with docker.
We'll need to run the following command in our current working base directory to build an image.
sudo docker build -t ubuntu:Apache_Server .
You should see the following output:
Sending build context to Docker daemon 8.704 kB Step 1 : FROM ubuntu ---> 3876b81b5a81 Step 2 : RUN apt-get update -y && apt-get install apache2 apache2-utils -y ---> Running in a7173526f87f ---> ea72a4d99ae3 Removing intermediate container a7173526f87f Step 3 : EXPOSE 80 ---> Running in dc180eaaf5d2 ---> a4f48bbe6995 Removing intermediate container dc180eaaf5d2 Step 4 : ENTRYPOINT /usr/sbin/apache2ctl ---> Running in e0a28430e4b2 ---> 77a8fc26d2f9 Removing intermediate container e0a28430e4b2 Step 5 : CMD -D FOREGROUND ---> Running in 292651b9259b ---> 6466197ee4df Removing intermediate container 292651b9259b Successfully built 6466197ee4df
-t parameter used to tag the Docker image. The
. parameter is used to specify the location of the Dockerfile that we created.
After building Apache_Server image, run docker images command:
sudo docker images | grep -i Apache_Server
You should see the Apache_Server image listed in the output as shown below:
ubuntu Apache_Server 6466197ee4df 2 minutes ago 224.1 MB
Creating a Docker Container
Using the image we have built, we will now proceed to create a container running an Apache instance inside, using a name of our choice. Here we will use Apache_Instance.
Run following command to create a container:
sudo docker run --name Apache_Instance -p 80:80 -d ubuntu:Apache_Server
Finally, we have created our Apache Container and it is forwarded to port
80. Now to check if its running properly or not we can run docker ps command.
sudo docker ps
You should see the following output:
f49877210e7d ubuntu:Apache_Server "/usr/sbin/apache2ctl" 2 minutes ago Up 2 minutes 0.0.0.0:80->80/tcp Apache_Instance
After setting everything up, you can verify the Apache Web Server by typing the url
http://localhost:80 in your web browser.