[Supplement][Docker] Building and Managing Docker Images

 

A Docker image is a read-only template that contains everything needed to run a container, including the application, libraries, and configuration files. This guide outlines efficient methods for building and managing Docker images.

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1. Building a Docker Image

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1.1 Writing a Dockerfile

A Docker image is created based on a Dockerfile.

Here is a basic example:

# Set base image
FROM python:3.9

# Set working directory
WORKDIR /app

# Copy dependencies and install required packages
COPY requirements.txt .
RUN pip install -r requirements.txt

# Copy application files
COPY . .

# Define the command to run the application
CMD ["python", "app.py"]

 

1.2 Building a Docker Image

To build an image using the above Dockerfile, run:

docker build -t myapp:latest .

Explanation of options:

• -t myapp:latest → Assigns the name myapp with the tag latest.
• . → Uses the Dockerfile in the current directory.

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2. Managing Docker Images

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2.1 Listing Docker Images

To check available Docker images:

docker images

 

2.2 Deleting a Docker Image

To remove a specific image:

docker rmi [image-name] # Or use the image ID

 

2.3 Changing an Image Tag

To tag an existing image with a new repository and version:

docker tag myapp:latest myrepo/myapp:v1.0

2.4 Uploading an Image to Docker Hub or a Private Registry

 

To upload an image to Docker Hub, first log in:

docker login

Then, push the image:

docker push myrepo/myapp:v1.0

 

For private registries, include the registry address:

docker tag myapp:latest myregistry.com/myapp:v1.0 docker push myregistry.com/myapp:v1.0

 

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3. Optimizing Docker Images

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3.1 Using Multi-Stage Builds

To minimize image size, use multi-stage builds:

# Build stage 
FROM node:18 AS builder 
WORKDIR /app 
COPY package.json . 
RUN npm install COPY . . 
RUN npm run build 

# Runtime stage 
FROM nginx:alpine 
COPY --from=builder /app/build /usr/share/nginx/html

 

This approach prevents unnecessary files from being included in the final image.

3.2 Excluding Unnecessary Files

Create a .dockerignore file to prevent unwanted files from being copied:

node_modules
*.log
.git

 

3.3 Using Lightweight Base Images

Using minimal base images reduces overall image size:

• Instead of python, use python:alpine.
• Instead of ubuntu, use debian or alpine.

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Summary

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Task	Command /Concept
Build an image	docker build -t myapp:latest .
List images	docker images
Remove an image	docker rmi [image-name]
Tag an image	docker tag myapp:latest myrepo/myapp:v1.0
Push to Docker Hub	docker push myrepo/myapp:v1.0
Use Multi-Stage Builds	Reduces final image size
Exclude unnecessary files	Use .dockerignore
Use lightweight images	Prefer alpine or debian over ubuntu

 

Following these best practices ensures efficient Docker image management and optimized container deployments.