Docker for Devops

Here are detailed notes on each Docker topic based on your PDF content:

### 1. Introduction to Docker

- Overview:

?- Released in March 2013 by Solomon Hykes and Sebastien Paul.

?- Open-source platform for creating, deploying, and running applications.

?- Utilizes OS-level virtualization through containers rather than creating full virtual machines.

?- Docker can be installed on any OS, but the Docker engine runs natively on Linux distributions.

?- Written in the Go programming language.

- Key Concepts:

?- Containerization: Running applications in isolated environments called containers.

?- Docker vs. Virtual Machines: Containers share the host OS kernel, making them more lightweight compared to VMs that require separate OS instances.

### 2. Benefits of Using Docker

- Advantages:

?- No Pre-allocation of RAM: Containers use resources on-demand.

?- CI Efficiency: Reusable images streamline the deployment process.

?- Cost-effective: Reduces overhead compared to traditional VM setups.

?- Lightweight: Quick to start and stop, minimal resource usage.

?- Flexibility: Runs on physical, virtual, or cloud hardware.

?- Image Reusability: Images can be shared and reused across environments.

### 3. Challenges with Docker

- Disadvantages:

?- Not ideal for applications requiring a rich graphical user interface (GUI).

?- Managing a large number of containers can become complex.

?- Cross-platform compatibility issues; an image built on one OS may not run on another.

?- Not a substitute for Virtual Machines when OS environments differ.

?- Lack of built-in solutions for data recovery and backup.

### 4. Docker Architecture and Components

- Components:

?- Docker Daemon: Runs on the host OS, manages containers, and communicates with other daemons.

?- Docker Client: Users interact with the daemon through commands and REST API.

?- Docker Host: Provides an environment to execute applications and contains the daemon, images, containers, networks, and storage.

?- Docker Registry: Stores Docker images (e.g., Docker Hub for public images).

### 5. Understanding Docker Images and Containers

- Images:

?- Read-only binary templates used to create containers.

?- Can be pulled from Docker Hub, created from Docker files, or derived from existing containers.

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- Containers:

?- Instances of Docker images in execution.

?- Act as lightweight virtualized environments.

### 6. Docker Installation and Basic Commands

- Installation:?

?- Use package managers (e.g., yum install docker on AWS).

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- Basic Commands:

?- docker images - List all images on local machine.

?- docker pull <image> - Download an image from Docker Hub.

?- docker run --name <container> <image> - Create and run a container with a name.

?- docker ps - List running containers.

?- docker stop <container> - Stop a running container.

?- docker rm <container> - Remove a container.

### 7. Creating and Using Dockerfiles

- Dockerfile:

?- A text file with a series of instructions to automate the image creation process.

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- Common Instructions:

?- FROM: Specifies the base image.

?- RUN: Executes commands to create layers in the image.

?- COPY: Copies files from the local system into the image.

?- ADD: Similar to COPY, but can fetch files from URLs.

?- EXPOSE: Defines which ports the container will listen on.

?- CMD and ENTRYPOINT: Specify the commands to run in the container.

### 8. Working with Docker Volumes

- Volume Management:

?- Volumes are directories that persist data beyond the lifecycle of a container.

?- Can be shared between containers and mapped to the host system.

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- Benefits:

?- Decouples storage from containers, allowing data persistence and sharing.

?- Volumes remain intact even after the container is deleted.

### 9. Docker Networking and Port Management

- Networking:

?- Containers can communicate over a network through exposed ports.

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- Port Management:

?- EXPOSE: Makes a port available for communication between containers.

?- -p: Publishes a port to the host, making it accessible externally.

### 10. Advanced Docker Commands and Usage

- Commands:

?- docker exec: Executes commands in a running container.

?- docker attach: Connects to the main process of a running container.

### 11. CI/CD with Docker

- Continuous Integration/Deployment:

?- Docker enables consistent environments across development, testing, and production stages.

?- Streamlines the CI/CD pipeline by allowing the same image to be used throughout.

### 12. Comparing Docker with Virtual Machines

- Differences:

?- Docker containers are lightweight and share the host OS kernel, while VMs run separate OS instances.

?- Docker provides faster startup times and resource efficiency compared to traditional virtualization.