# A Hands on Docker Tutorial

## **What is Docker?**

Docker is a tool that makes it easier to create, deploy, and run applications using containers.

A docker container is a collection of dependencies and code organized as software that enables applications to run quickly and efficiently in a range of computing environments.

A docker image, on the other hand, is a blueprint that specifies how to run an application. In order for Docker to build images automatically, a set of instructions must be stored in a special file known as a Dockerfile.

![image.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1657349949517/Ory0MH7Ma.png align="left")

## ** Who is this for? **

Do you find yourself in a position where you ask yourself ok I've understood what docker does, but how do I build a simple docker image and publish it on docker hub.
Then you have come to the right place!!😀

### ** Python Setup **

Assuming you have already installed python create a python file and paste the below code in that file

```
ip1 = int(input("Enter the first number:")) 
ip2 = int(input("Enter the second number:"))
choice = int(input("Enter the operation needs to be performed: 1.Add 2.Sub 3.Mul 4.Div"))    

def add(num1, num2):
    return num1+num2
def sub(num1, num2):
    return num1-num2
def mul(num1, num2):
    return num1*num2
def div(num1, num2):
    return num1/num2

if choice == 1:
    print(add(ip1, ip2))
elif choice == 2:
    print(sub(ip1, ip2))
elif choice == 3:
    print(mul(ip1, ip2))
elif choice == 4:
    print(div(ip1, ip2))
else:
    print("Invalid choice")
        
``` 

### Writing the dockerfile 

 
```
FROM ubuntu:latest

RUN apt update && apt upgrade -y

RUN apt install python3 -y

COPY . /app

WORKDIR /app

CMD ["python3", "main.py"]

``` 

### Building and Pushing Image to DockerHub

Now head over to the current working directory and open the terminal and type this command to build the image.

```
docker build -t <repo-name/app-name-demo:tagname>
# An Example would be
docker build -t user10/calculator-demo:v1
```
On issuing command, you should see your container
```
docker images
```

![image.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1657380913057/ga5QkzdAd.png align="left")

You can run the docker container by using 
```
 docker run -it repo-name/app-name-demo:tagname

```

Now push this docker image to the dockerhub by typing this command

```
 docker push repo-name/app-name-demo:v1
```

Make sure you have given the same docker image, app and tag name while building and pushing. You might stumble across this error if give a wrong name.

![image.png](https://cdn.hashnode.com/res/hashnode/image/upload/v1657381486789/PUxqJzyaU.png align="left")

If you have made it till here kudos to you🎉🎉😀

## Thank You