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https://github.com/praem90/docker-introduction

An introduction to Docker for beginners
https://github.com/praem90/docker-introduction

container docker images network port

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An introduction to Docker for beginners

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README 

        
# Docker



## Topics

 * What is Docker?

 * Why do we need Docker?

 * Key components of a Docker

 * Image

 * Container

 * Network

 * Volume



---



## What is Docker?

 - Docker is an open-source software platform that enables developers to build, deploy, run, update, and manage containers.

 - Docker uses OS-level virtualization to deliver software in packages called containers.

 - Docker standardized executable components that combine application source code with

   the operating system libraries and dependencies required to run that code in any *environment*.



---



## Why do we need Docker?

 - Docker enables you to separate your applications from your infrastructure so you can deliver software quickly.

 - Docker's container-based platform allows for highly portable workloads.

 - Docker containers can run on a developer's local laptop, on physical or virtual machines in a data center, on cloud providers, or in a mixture of environments.

 - Docker's portability and lightweight nature also make it easy to dynamically manage workloads, scaling up or tearing down applications and services as business needs dictate, in near real time.



---



## Questions



 Any questions?



---



## Docker Objects

When you use Docker, you are creating and using images, containers, networks, volumes, plugins, and other objects. This section is a brief overview of some of those objects.



---



### Images

 - An image is a read-only template with instructions for creating a Docker container.

 - Often, an image is based on another image, with some additional customization.

 - For example, you may build an image which is based on the ubuntu image, but installs the Apache web server

 - and your application, as well as the configuration details needed to make your application run.

 - You might create your own images or you might only use those created by others and published in a registry.



An image is like a class. It is just a blueprint with set of instructions to create a container.



|Class       | Image/Dockerfile |

|:----------:|:----------------:|

| Class Car {                    |FROM ubuntu    |

|    private wheels;            | RUN apt-get install nginx |

|    private steering;          |

|    private fuel;              |

|                               |

|    public function move() {   |

|    }                          |

| }                             |



---



### Container

- A container is a runnable instance of an image.

- You can create, start, stop, move, or delete a container using the Docker API or CLI.

- You can create multiple containers using the same image



| Instance | Container |

|:--------:|:---------:|

| $car = new Car() | docker run ubuntu |



```bash

 docker run bash:latest bash -c "date > file.txt && cat file.txt"

```



---



## Questions



 Any Questions?



---



### Network

 - Container networking refers to the ability for containers to connect to and communicate with each other, or to non-Docker workloads.

 - By default, when you create or run a container using docker create or docker run, the container doesn't expose any of its ports to the outside world.

 - Use the --publish or -p flag to make a port available to services outside of Docker.

 - This creates a firewall rule in the host, mapping a container port to a port on the Docker host to the outside world.



---



#### Port

```bash

docker run nginx

docker ps

```



You wont be able to access the nginx server http://localhost



```bash

docker run -p 80:80 nginx

docker ps

```



Now we will be able to access the nginx server via http://localhost:80



```bash

docker run -p 8989:80 nginx

docker ps

```



We can bind different port for host machine.

Docker will act as proxy and serves the data.



Now we wont be able to access via port 80 but http://localhost:8989



---



#### Network Drivers

 - Docker's networking subsystem is pluggable, using drivers. Several drivers exist by default, and provide core networking functionality.

    * bridge // the default network driver

    * host

    * overlay

    * ipvlan

    * macvlan

    * none



```bash

docker run bash bash -c "wget http://localhost:80"

```

Nginx wont be accessible from the bash container.

the localhost refers to the same bash container not the nginx container.

The nginx container has its own ip inside the network



```bash

docker run --network=bridge -d nginx

docker container inspect 'name_of_the_container' | grep IPAddress

docker run --network=bridge bash bash -c "wget http://ip_address_of_the_nginx_container:80"

```



---



### Volume

 - While containers can create, update, and delete files, those changes are lost when you remove the container and Docker isolates all changes to that container.

 - With volumes, you can change all of this.

 - Volumes provide the ability to connect specific filesystem paths of the container back to the host machine.

 - If you mount a directory in the container, changes in that directory are also seen on the host machine.

 - If you mount that same directory across container restarts, you'd see the same files.



 E.g:

 Did you able to get the `file.txt` from the above command



 ```bash

 docker run -it bash:latest bash -c "date > file.txt && cat file.txt && bash"

 docker run -it -w /app -v $(pwd):/app bash:latest bash -c "date > file.txt && cat file.txt && bash"

 ```

 Now you can see the files in this host folder will be available in the containers `/app` directory and vice versa.

 There are different types of volume and different ways to mount a volume to a container.



 ---



## Questions



 Any Questions?