Docker tool is a vital part of the configuration management tool in most of the global companies. Docker tool runs an application with the help of dockerfile with a high level of abstraction and security. Hence, many companies are extensively adopting the tool to achieve high network availability, service continuity, and service provision with high scalability.
However, global news wire has confirmed that the demand for docker tools in the market will eventually grow from USD 217 million to USD 993 million by 2024. This growth is exponential.
The reason for Docker being so popular is Docker image, Docker container and Dockerfile. However, Docker Image can be created only with the help of Dockerfiles. Moving forward, let us understand docker and dockerfile in detail.
What is Docker?
Docker is a configuration management tool that is used to automate the deployment of software in lightweight containers. These containers help applications to work efficiently in different environments.
Features of Docker:
- Easy and faster configuration
- Application isolation
- Security management
- High productivity
- High scalability
- Infrastructure independent
Docker container is a software package that has all the dependencies required to run an application.
Note: A Docker Image is a template of instructions used to create containers
What is a Dockerfile?
Before we discuss what is a Dockerfile, it is important to know what a Docker image is.
A Docker Image is a read-only file with a bunch of instructions. When these instructions are executed, it creates a Docker container.
Dockerfile is a simple text file that consists of instructions to build Docker images.
Mentioned below is the syntax of a Dockerfile:
command argument argument1...
# Print "Get Certified. Get Ahead"
Run echo "Get Certified. Get Ahead"
Now, let's have a look at how to build a Docker image using a dockerfile.
List of Docker Commands for Creating a Dockerfile
Before we create our first Dockerfile, it is important to understand what makes up the file.
Dockerfile consists of specific commands that guide you on how to build a specific Docker image.
The specific commands you can use in a dockerfile are:
FROM, PULL, RUN, and CMD
- FROM - Creates a layer from the ubuntu:18.04
- PULL - Adds files from your Docker repository
- RUN - Builds your container
- CMD - Specifies what command to run within the container
Mentioned below is an example of the dockerfile with the important commands
RUN make /file
CMD python /file/file.py
Have a look at the diagrammatic representation of how a dockerfile looks in a docker image:
Moving forward, let’s go through some of the most common Docker commands used while creating dockerfiles. Along with the syntax, we are explaining the commands with examples, so you can start experimenting with them right away.
- ENTRYPOINT allows specifying a command along with the parameters
ENTRYPOINT application "arg, arg1".
ENTRYPOINT echo "Hello, $name".
- ADD command helps in copying data into a Docker image
- ENV provides default values for variables that can be accessed within the container
ENV key value
- MAINTAINER declares the author field of the images
How to Build a Docker Image and Docker Container Using Dockerfile?
First of all, you should create a directory in order to store all the Docker images you build.
- Now, we will create a directory named ‘simplidocker’ with the command:
- Move Docker image into that directory and create a new empty file (Dockerfile) in it:
- Open the file with the editor. In this example, we opened the file using vi:
- Then, add the following content:
RUN apt-get update
CMD ["echo", "Welcome to Simplilearn"]
- 5.Save and exit the file.
Build a Docker Image with Dockerfile
Let’s first declare the path where we will be storing the dockerfile simplidocker
docker build [OPTIONS] PATH | URL | -
Now, let’s build a basic image using a Dockerfile:
docker build [location of your dockerfile]
Now, by adding -t flag, the new image can be tagged with a name:
docker build -t simpli_image
Once the Docker image is created, you can verify by executing the command:
The output should show simpli_docker available in the repository.
Create a New Container
Now, create a Docker container from the Docker image we created in the previous step.
Let’s name the container “simplilearn” and create it with the command:
docker run --name simplilearn simpli_docker
The message ‘Welcome to Simplilearn’ should appear in the command line, as seen in the image above.
Congratulations, you just created a Docker image and a Docker container using a Dockerfile.
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With that, we have come to the end of the article, what is dockerfile. In this write-up, we discussed what docker is, what is dockerfile, syntax of dockerfile, important commands to create a docker image using a dockerfile, and how to build a docker image using a dockerfile.
If you are keen on furthering your knowledge with an in-depth understanding of the Docker tool, Simplilearn can be an ideal destination for you. This Docker In-Depth Training Course helps interested individuals learn both the basic and advanced concepts of Docker. By completing this certification program, you will gain hands-on experience on creating flexible application environments with Docker.
Do you have any doubts about this topic? Please feel free to place your questions in the comments section of this ‘What Is Dockerfile’ article. Our subject matter experts will get back to you at the earliest, on the same!