Docker-Day-1-Free-trail

### Project Scenario: Installing Docker and Validating Basic Commands

1. Install Docker using `yum`:

sudo yum install docker -y

Explanation: Installs Docker using the `yum` package manager.

Validation:

docker --version

Explanation: Checks if Docker is installed correctly by displaying the installed Docker version.

2. Start the Docker service:

sudo systemctl start docker

Explanation: Starts the Docker service.

Validation:

sudo systemctl status docker

Explanation: Verifies that the Docker service is running.

3. Enable Docker to start on boot:

sudo systemctl enable docker

Explanation: Configures Docker to start automatically on system boot.

Validation:

sudo systemctl is-enabled docker

Explanation: Confirms that Docker is enabled to start on boot.

4. Check available Docker images:

docker images

Explanation: Lists all Docker images currently available on the system.

Validation:

Explanation: If no images are listed, the output confirms that there are no pre-existing Docker images on the system.

5. Run a "Hello World" container:

docker run hello-world

Explanation: Pulls the "hello-world" image from Docker Hub and runs a container.

Validation:

Explanation: The output will show a message from Docker explaining that the installation is successful and from where the image was downloaded (Docker Hub).

6. Explain from where the image is downloaded:

Explanation: The "hello-world" image is downloaded from Docker Hub, Docker's official online repository for container images.

7. List running containers:

docker ps

Explanation: Shows all currently running Docker containers.

Validation:

Explanation: If the "hello-world" container ran successfully and has stopped, `docker ps` will show no running containers.

8. List all containers (including stopped ones):

docker ps -a

Explanation: Lists all containers, including those that have exited.

Validation:

Explanation: The "hello-world" container will be listed with an "Exited" status, indicating that it ran successfully and then stopped.

This scenario covers installing Docker, running a basic container, and validating each step to ensure everything is set up and working correctly.

### Project Scenario: to further explore Docker by running a container, assigning a name, and validating each step:

1. Run "Hello World" container again:

docker run hello-world

- Explanation: Runs the "hello-world" container again to check if Docker uses the locally cached image or downloads it again.

Validation:

- Explanation: If Docker uses the local image, the output will quickly show the success message without mentioning a download process. If it downloads the image again, it will show a progress bar.

2. Create a new container with an assigned name:

docker run --name my_hello_container hello-world

- Explanation: Creates and runs a new container from the "hello-world" image, assigning it the name `my_hello_container`.

Validation:

docker ps -a --filter "name=my_hello_container"

- Explanation: Checks if the container with the name `my_hello_container` exists, showing its details.

3. Check running containers:

docker ps

- Explanation: Lists all currently running Docker containers.

Validation:

- Explanation: If the "hello-world" container has stopped, `docker ps` will not show it in the list, confirming that no containers are currently running.

4. Check all containers (including stopped ones):

docker ps -a

- Explanation: Lists all containers, including those that have exited, giving a full view of the Docker containers on the system.

Validation:

- Explanation: The output will show the `my_hello_container` with an "Exited" status, confirming it was created and ran successfully.

This scenario walks you through running a Docker container, assigning it a custom name, and validating that Docker is utilizing the local image and managing containers correctly.

### Project Scenario: to explore Docker image search, naming conventions, and setting up a Docker Hub repository:

1. Search for Docker images using the `docker search` command:

docker search nginx

Explanation: Searches Docker Hub for images related to "nginx," displaying a list of available images.

Validation:

Explanation: The output will show a list of images, their descriptions, stars (ratings), and whether they are official images or not, confirming that the search function is working.

2. Explain Docker image naming convention:

Explanation: Docker image names follow the format `repository_name[:tag]`, where `repository_name` is the name of the image, and `tag` is an optional identifier, typically specifying the version. For example:

- `nginx:latest` refers to the latest version of the official Nginx image.

- `user/nginx:1.19` refers to version 1.19 of a user-specific Nginx image.

- `python:3.8-alpine` refers to the Python image with version 3.8, based on the Alpine Linux distribution.

3. Create a Docker Hub repository:

Explanation: Sign in to your Docker Hub account at [hub.docker.com](https://hub.docker.com/), navigate to "Repositories," and click "Create Repository."

Validation:

Explanation: Once created, the new repository will appear under "Repositories" on your Docker Hub dashboard, confirming that the repository setup was successful.

This scenario covers searching for Docker images, understanding naming conventions, and creating a Docker Hub repository.

### Project Scenario: Pulling, Tagging, and Pushing an Nginx Image to Docker Hub

1. Pull the Nginx image from Docker Hub:

docker pull nginx:latest

Explanation: Downloads the `nginx:latest` image from Docker Hub to your local system.

Validation:

docker images | grep nginx

Explanation: Verifies that the `nginx:latest` image has been successfully downloaded by listing it among your Docker images.

2. Tag the Nginx image with `test_tag`:

docker tag nginx:latest your_dockerhub_username/nginx:test_tag

Explanation: Tags the `nginx:latest` image with the name `your_dockerhub_username/nginx:test_tag`, preparing it for upload to Docker Hub.

Validation:

docker images | grep nginx | grep test_tag

Explanation: Confirms that the image has been tagged with `test_tag` by displaying it under the new name.

3. Log in to Docker Hub from Linux Terminal(EC2 Instance):

docker login

Explanation: Prompts you to enter your Docker Hub credentials for authentication.

Validation:

Explanation: Upon successful login, Docker will display a message saying "Login Succeeded."

4. Push the tagged Nginx image to Docker Hub:

docker push your_dockerhub_username/nginx:test_tag

Explanation: Uploads the tagged image `your_dockerhub_username/nginx:test_tag` to your Docker Hub repository.

Validation:

Explanation: After the push completes, Docker Hub will display the upload progress, confirming that the image has been successfully pushed.

5. Check the image on Docker Hub:

Explanation: Visit [hub.docker.com](https://hub.docker.com/) and navigate to your repository to confirm that the `nginx:test_tag` image appears under your Docker Hub account.

Validation:

Explanation: The presence of the `nginx:test_tag` image in your repository on Docker Hub confirms that the push was successful and the image is now publicly or privately available depending on your repository settings.

This scenario walks you through pulling an Nginx image, tagging it, logging in to Docker Hub, pushing the image, and verifying its presence on Docker Hub.

The `/root/.docker/config.json` file is a configuration file used by Docker to store credentials, settings, and preferences related to Docker CLI operations for the root user. This file typically contains information such as:

- Docker Hub Credentials: Stored when you log in using `docker login`. These credentials allow Docker to interact with Docker Hub or other private registries without requiring you to log in every time.

- Auth Configurations: For connecting to private Docker registries.

- CLI Preferences: Settings related to how Docker CLI commands behave.

### Common Issues and Fixes with `/root/.docker/config.json`

1. Corrupt or Invalid Configuration File:

- Issue: The file may become corrupt or have invalid JSON syntax, causing errors when Docker tries to read it.

- Fix:

- Backup the existing file:

cp -p /root/.docker/config.json /root/.docker/config.json.bak

- Delete or repair the file:

If you suspect corruption, you can delete the file and regenerate it by logging in again:

rm /root/.docker/config.json

docker login

2. Permission Issues:

- Issue: Incorrect file permissions may prevent Docker from accessing the file.

- Fix:

- Set correct permissions:

sudo chmod 600 /root/.docker/config.json

- *Explanation*: Ensures that the file is readable and writable only by the root user.

3. Authentication Errors:

- Issue: Errors related to authentication (e.g., "Error saving credentials" or "unauthorized: incorrect username or password").

- Fix:

- Re-login:

docker logout

docker login

- *Explanation*: Logs out from Docker Hub and then logs in again to refresh the credentials stored in `config.json`.

### Summary

The `/root/.docker/config.json` file is crucial for Docker's authentication and configuration management. If you encounter issues with this file, you can often resolve them by repairing the file, adjusting permissions, or re-authenticating. Always keep a backup of the file before making significant changes.