Docker

Terminologies

1. Containers vs. Images:

Containers are instances of Docker images.

Images are read-only templates with everything needed to run an application.

2. Dockerfile:

Dockerfiles are used to create custom Docker images.

They define the environment and dependencies of your application.

3. Docker Hub:

Docker Hub is a public registry where you can find and share Docker images.

4. Docker Commands:

docker pull <image_name>: Pulls an image from a registry.

docker run <image_name>: Creates and starts a container from an image.

docker ps: Lists running containers.

docker images: Lists downloaded images.

docker build -t <image_name> .: Builds a Docker image from a Dockerfile in the current directory.

docker stop <container_id>: Stops a running container.

docker rm <container_id>: Removes a container.

docker rmi <image_name>: Removes an image.

docker exec -it <container_id> <command>: Executes a command inside a running container.

5. Port Mapping:

You can map host machine ports to container ports using the p option with docker run.

6. Volume Mounting:

Use v or -volume to mount directories or files from the host machine into a container.

7. Networking:

Containers can communicate with each other using their container names.

8. Docker Compose:

Docker Compose is a tool to define and run multi-container applications.

Define services, networks, and volumes in a docker-compose.yml file.

9. Container Lifecycle:

Containers are ephemeral; they can be stopped and removed without losing data by using volumes.

10. Docker Registry:

Besides Docker Hub, you can set up private Docker registries for your organization's images.

11. Docker Swarm and Kubernetes:

Docker Swarm and Kubernetes are tools for orchestrating and managing multiple containers in production environments.

12. Docker Best Practices:

Keep images small and focused on a single task.

Avoid running multiple processes in a single container.

Use environment variables for configuration.

Regularly update base images and dependencies.

13. Docker Security:

Keep Docker and the host system updated.

Use Docker's built-in security features like namespaces and cgroups.

14. Monitoring and Logging:

Use Docker monitoring and logging tools or integrate with external solutions.

15. Backup and Recovery:

Regularly back up data volumes to prevent data loss.

16. Dockerfile Best Practices:

Use official base images when possible.

Minimize the number of layers in your image.

Clean up unnecessary files in each image layer.

17. Docker Registry Authentication:

Securely manage credentials for private registries using docker login.

18. Docker Image Tagging:

Use meaningful tags to version your images.

19. Docker Networking:

Understand bridge networks, host networks, and user-defined networks for container communication.

20. Docker Troubleshooting:

Use docker logs <container_id> to view container logs.

Docker provides detailed error messages for most issues.

Docker Commands

Docker is a powerful containerization platform that allows you to package and distribute applications and their dependencies in a portable and consistent way. Here are some of the most important Docker commands and their explanations:

docker run: This command is used to create and start a new container from a Docker image. For example:


docker run -d --name my_container nginx

d: Run the container in detached mode (in the background).

-name: Assign a name to the container.

nginx: The name of the Docker image to use.

docker pull: Used to download a Docker image from a registry (like Docker Hub) to your local machine. For example:


docker pull nginx

docker build: This command is used to build a Docker image from a Dockerfile. A Dockerfile is a text file that contains instructions on how to create an image. For example:


docker build -t my_custom_image .

t: Assign a name and optionally a tag to the image.

.: The path to the directory containing the Dockerfile.

docker ps: Lists all running containers. You can use options like a to list all containers, including stopped ones.


docker ps

docker stop and docker start: These commands are used to stop and start containers, respectively.


docker stop my_container
docker start my_container

docker exec: Allows you to run commands inside a running container. For example, to get a shell inside a container:


docker exec -it my_container bash

it: Allocate a pseudo-TTY and keep STDIN open even if not attached.

docker images and docker rmi: The docker images command lists all the Docker images available on your system, and docker rmi is used to remove images.


docker images
docker rmi my_custom_image

docker logs: View the logs generated by a container.


docker logs my_container

docker network: Manage Docker networks, allowing you to connect containers together.

docker-compose: Docker Compose is a tool for defining and running multi-container Docker applications. It uses a YAML file to configure application services, networks, and volumes.


docker-compose up

This command will start all the services defined in your docker-compose.yml file.

These are some of the fundamental Docker commands, but Docker offers a wide range of features and options for container management and orchestration. To learn more, you can explore the official Docker documentation and tutorials.

docker run: Start a new container instance from a Docker image.


docker run [OPTIONS] IMAGE [COMMAND] [ARG...]

docker ps: List running containers.


docker ps [OPTIONS]

docker images: List available Docker images.


docker images [OPTIONS]

docker pull: Download a Docker image from a registry.


docker pull IMAGE_NAME[:TAG]

docker build: Build a Docker image from a Dockerfile.


docker build [OPTIONS] PATH | URL | -

docker stop: Stop a running container.


docker stop CONTAINER_ID

docker start: Start a stopped container.


docker start CONTAINER_ID

docker restart: Restart a container.


docker restart CONTAINER_ID

docker rm: Remove one or more containers.


docker rm CONTAINER_ID

docker rmi: Remove one or more images.


docker rmi IMAGE_NAME

docker exec: Run a command inside a running container.


docker exec [OPTIONS] CONTAINER COMMAND [ARG...]

docker logs: View logs from a container.


docker logs CONTAINER_ID

docker network: Manage Docker networks for container communication.


docker network [SUBCOMMAND]

docker-compose: Define and run multi-container Docker applications using a Compose file.


docker-compose [OPTIONS] [COMMAND] [ARGS...]

Dockerfile: A script that contains instructions for building a Docker image.

Docker Registry: A repository for Docker images (e.g., Docker Hub).

Docker Hub: A public registry for Docker images where you can find and share Docker images.

Containers: Lightweight, isolated environments created from Docker images.

Volumes: Persistent data storage for containers, allowing data to survive container restarts.

Ports: Specifying port mappings to expose container services to the host.

Start a Node application in a container

The error message you're encountering suggests that the npm tracker "idealTree" already exists, which typically happens when there's a conflict or issue with the npm cache. To fix this issue, you can try the following steps:

Clear npm cache:


# Use a base image with Node.js pre-installed
FROM node:14-alpine

# Set the working directory in the container
WORKDIR /app

# Copy package.json and package-lock.json to the working directory
COPY package*.json ./

# Clear the npm cache
RUN npm cache clean --force

# Install some dependencies
RUN npm install

# Copy the rest of your application code
COPY ./ ./

# Default command
CMD ["npm", "start"]

Rebuild the Docker image:

After making this change, rebuild your Docker image to apply the modifications:


docker build -t your-image-name .

Run the container:

Once the image is successfully built, you can run your container as usual:


docker run -p 3000:3000 your-image-name