Complete Docker Guide: Learn How to Create and Manage Containers for Scalable Applications

Docker has become an essential tool in the world of development and systems administration, allowing the creation, distribution, and execution of applications in isolated and consistent environments. In this comprehensive guide, we will explore from the basics of Docker to practical examples of different use cases, including content from Docker Hub.

Introduction to Docker

Docker is a lightweight virtualization platform that allows packaging and distributing applications along with all their dependencies in containers. A container is a software unit that includes everything needed to run an application, including code, runtime, libraries, and configurations.

Advantages of using Docker

Portability: Containers can run on any machine that has Docker installed.
Isolation: each container operates in an isolated environment, preventing conflicts between applications.
Scalability: Containers can be easily replicated to handle variable workloads.
Consistency: Ensures that the application works the same way in different environments.

Key concepts: images and containers.

Image: Template that contains a filesystem and necessary configurations to run an application.
Container: Running instance of an image. It is an isolated environment.

Docker Installation.

To install Docker, it depends on the operating system. It is available for Linux with any distribution such as Ubuntu, CentOS, Kali, etc., also available for Windows and MacOS. To install it, just follow the steps depending on the operating system you have at this link: https://docs.docker.com/engine/install/

Basic Docker Commands

docker run

The ‘docker run’ command is used to run a container from an image. For example:


docker run -d -p 80:8080 nginx

This command runs a container based on the “nginx” image in the background and maps port 8080 of the container to port 80 of the host.

💡Note: The ‘-d’ detach flag is generally used to continue using our terminal, since if it is not used, you have to stop the container to continue using the command line.

docker ps

Shows a list of running containers.


docker ps

docker ps -a

Shows the list of containers that are running and stopped over time.


docker ps -a

docker images

Lists the images available on the system.


docker images

docker build

Builds an image from a Dockerfile in the current directory.


docker build -t "my-app"

docker stop and docker start

Stops and starts a running container.


docker stop "container-name"
docker start " container-name"

Creating and managing Images

A Dockerfile is a text file that defines how an image will be built. Example of a Dockerfile for a Node.js application



FROM node:18.17-alpine

WORKDIR /app

COPY package.json yarn.lock ./

RUN npm install

COPY . .

EXPOSE 3000

CMD [ "npm", "start" ]

Here we can see an example showing a series of instructions that our Dockerfile will have

FROM: provides us with a base image. In this case, we take the 18.17-alpine image, which is much lighter than node 18.17
WORKDIR: this is where our application will be hosted in the container
COPY: adds the files from our local directory, all dependencies so that there are no errors when building
RUN: creates the application with node:18.17-alpine
EXPOSE: this is where our application will be exposed, in this case on port 3000
CMD: Specifies which command we want to run in the container

💡Note: there is another instruction called ENTRYPOINT, which is the entry to execute in the container; as an example, it would look like this


FROM node:18.17-alpine

WORKDIR /app

COPY package.json yarn.lock ./

RUN npm install

COPY . .

EXPOSE 3000

ENTRYPOINT [ "npm" ]

CMD [ "start" ]

Networks in Docker

Types of Networks in Docker

Bridge: internal private network for containers on the same host.
Host: Shares the host's network with the container
Overlay: Multi-host network for communication between containers on different hosts.

Create and Manage Networks


docker network create "my-network"

Connect Containers to Networks


docker run -d --network="my-network" --name="my-container-nginx"

Data Persistence

Mounting Volumes in Containers

Allows data to persist even after stopping or deleting a container.


docker run -d -v "my-volume":/path/.../.../"my-container-nginx"

Data in Container vs Data in Volume

Data in the container is volatile and lost when the container is deleted. Data in a volume persists.

Copying data to/from Containers


docker cp file.txt "container-name":/path/.../.../container/
docker cp "container-name":/path/.../.../container/file.txt .

Practical Use Cases

Deploying a Web Application with Nginx


version: '3'
services:
  web:
    image: nginx
    ports:
      - "80:80"

Databases in Containers: MySQL and MongoDB


version: '3'
services:
  mysql:
    image: mysql:latest
    environment:
      MYSQL_ROOT_PASSWORD: mysecretpassword
  mongodb:
    image: mongo:latest
    volumes:
      - mongo-data:/data/db
volumes:
  mongo-data:

Isolated Development Environments

Creates consistent development environments for different projects


FROM node:14

WORKDIR /app

COPY package*.json ./

RUN npm install

COPY . .

CMD ["npm", "start"]

Container Orchestration with Kubernetes

Kubernetes is a powerful tool for container orchestration and management in a production environment

Exploring Docker Hub

Docker Hub is a public repository of container images, where individuals and companies can publish solution images.

Steps to Upload an Image to Docker Hub

The first thing you need to upload an image to Docker Hub is an account,

Create your account on Docker Hub:

If you don’t have your Docker Hub account yet, go to https://hub.docker.com/ and register

Install Docker on your local machine:

To install Docker on your system, download and install it from the official website of Docker https://www.docker.com/get-started/

Log in to Docker Hub from the command line

Open a terminal and use the following command to log in to Docker Hub with your username and password


docker login

You will be prompted to enter your Docker Hub username and password

Tag the image you want to upload

Make sure the image you want to upload has an appropriate tag. You can tag the image using the following command


docker tag "name_image":tag "user_docker_hub"/"name_image":tag

Example:



docker tag my_app:v1 robpalacios1/my_app:v1

Push the image to Docker Hub

Use the following command to push your tagged image to Docker Hub:



docker push "user_docker_hub"/"name_image":tag

Example


docker push robpalacios1/my_app:v1

Verify the image on Docker Hub

After the image push is completed successfully, you can check the repository on Docker Hub, in the repositories section to make sure the image is available

💡Note: As you can see, I have a React repository on my Docker Hub with different versions I have made in the code, and just by doing a pull to your local you can contribute to the code, similar to GitHub with the command docker pull robpalacios1/react-docker:<Tag>

Where Tag can be the versions I have from 1.0.0 up to the latest which is latest

Conclusion

Docker is a technology that has evolved the way we develop, deploy, and manage applications. From creating images to managing networks and volumes, Docker provides the necessary tools to build consistent and efficient environments.

Ready to take your applications to the next level with Docker?

At Kranio, we have experts in containerization and DevOps who will help you implement efficient solutions using Docker, optimizing your development processes and ensuring the scalability of your applications. Contact us and discover how we can drive the digital transformation of your company.