Steps to create, test and push a docker image

Download and install Docker Desktop. If on Linux, download Docker Engine - Community.
Create a Docker file with the name Dockerfile or download one.

Simple docker file example

  FROM ubuntu:18.04
  RUN apt-get update
  RUN apt install -y python3
  RUN python3 --version

Official Example
Advanced Example
```
  >notepad Dockerfile
```

Make changes to docker file and build it

 >docker build --rm -t krishan_apex:latest .
    
 Sending build context to Docker daemon  3.584kB
 **** installs a bunch of packages ***
 **** installs some more packages ***
 Successfully built 4a4cc017fe68

See the list of docker images

 > docker images
 REPOSITORY                           TAG                                        IMAGE ID            CREATED             SIZE
 krishan_apex                         latest                                     4a4cc017fe68        2 minutes ago       6.33GB

Create a repository in docker hub

Tag your image with <username>/<reponame>:<tag>

 > docker tag krishan_apex krishansubudhi/pytorch_apex:latest

Run the container on your machine using the image you just created.

 > docker run -it -d -p 5000:5000  krishansubudhi/pytorch_apex:latest

Check all running docker containers

 > docker ps
    
 CONTAINER ID        IMAGE                                COMMAND             CREATED             STATUS              PORTS                                                  NAMES
 55c7cfc80e35        krishansubudhi/pytorch_apex:latest   "/bin/bash"         15 seconds ago      Up 13 seconds       5001/tcp, 8883/tcp, 0.0.0.0:5000->5000/tcp, 8888/tcp   angry_elbakyan

Log in to terminal of runing container and run simple linux commands.
```
 docker attach 55c7cfc80e35
```
Push the image to dockerhub repo to be accessed by everyone. This takes a long time.
```
docker push krishansubudhi/pytorch_apex:latest
```

Reference :

IBM tutorial Official documentation What is Docker. RUN vs CMD vs ENTRYPOINT