Docker

Docker#

Core Components of Docker#

Docker Engine#

The Docker Engine is the core component that powers the Docker platform. It is responsible for creating, managing, and orchestrating containers. It consists of a daemon process (dockerd), a REST API, and a command-line interface (CLI).

Docker Images#

Docker images are read-only templates containing the application code, dependencies, libraries, and configuration files required to create and run a container. Images are stored in Docker registries and can be pulled to create containers.

Docker Containers#

A Docker container is a lightweight, standalone, and executable software package created from a Docker image. It includes everything needed to run an application, ensuring consistency across different environments.

Dockerfile#

A Dockerfile is a script containing instructions to build a Docker image. It specifies the base image, dependencies, configurations, and any other settings necessary to create a custom image tailored to your application.

Docker Registry#

A Docker registry is a centralized storage location for Docker images. Docker Hub is a public registry maintained by Docker Inc., but you can also create private registries or use third-party solutions.

Installation#

Install Docker on your system by following the official installation guide:

Basic Docker Commands#

Pull an Image#

Download an image from a registry:

docker pull <image-name>

List Images#

Display all images available locally:

docker images

Create and Run a Container#

Create a container from an image and start it:

docker run -it --name <container-name> <image-name>

List Containers#

List all running containers:

docker ps

List all containers, including stopped ones:

docker ps -a

Stop a Container#

Stop a running container:

docker stop <container-name>

Remove a Container#

Remove a stopped container:

docker rm <container-name>

Remove an Image#

Remove an unused image:

docker rmi <image-name>

Building Docker Images with Dockerfile#

Create a Dockerfile#

Create a file named Dockerfile in your project directory, and add instructions based on your application requirements.

Example Dockerfile:

# Use the official Python base image
FROM python:3.8-slim

# Set the working directory
WORKDIR /app

# Copy requirements file
COPY requirements.txt .

# Install dependencies
RUN pip install --no-cache-dir -r requirements.txt

# Copy application code
COPY . .

# Expose the application port
EXPOSE 8080

# Start the application
CMD ["python", "app.py"]

Build the Image#

Build the image from the Dockerfile:

docker build -t <image-name> .

Docker Compose#

Docker Compose is a tool for defining and running multi-container Docker applications. It allows you to configure your application’s services, networks, and volumes in a single docker-compose.yml file, simplifying the process of managing complex applications with multiple dependencies.

Install Docker Compose#

Follow the official installation guide:

Create a docker-compose.yml File#

Create a docker-compose.yml file in your project directory and define your application’s services, networks, and volumes.

Example docker-compose.yml file:

version: "3.8"

services:
  web:
    build: .
    ports:
      - "8080:8080"
  redis:
    image: "redis:alpine"

In this example, we have two services: web and redis. The web service is built from the current directory, and its port 8080 is mapped to the host’s port 8080. The redis service uses the official Redis image from Docker Hub.

Start Services#

Start all services defined in the docker-compose.yml file:

docker-compose up

Stop Services#

Stop all services:

docker-compose down

Docker Volumes#

Docker volumes are used to persist data generated by and used by Docker containers. They allow you to separate your application’s data from the container’s lifecycle, ensuring that your data remains intact even if the container is removed.

Create a Volume#

Create a new Docker volume:

docker volume create <volume-name>

Use a Volume in a Container#

To use a volume in a container, you need to mount it using the -v or --mount flag:

docker run -v <volume-name>:/data <image-name>

Conclusion#

Docker is a powerful platform that simplifies the process of building, deploying, and managing applications using containerization. Understanding its core components and commands, building custom images with Dockerfiles, managing multi-container applications with Docker Compose, and persisting data with Docker volumes will help you streamline your development workflow and ensure consistent application behavior across different environments.

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