能否用自定义Docker镜像制作新镜像？离线环境镜像构建方案咨询

1. Can I use or build a custom Docker image to create another image? #

Absolutely! This is one of the core strengths of Docker's layered architecture—you can absolutely use any custom image you’ve built (or even shared images from others) as the foundation for a new image, using the FROM directive in your Dockerfile.

Here’s a quick example to show how it works:

• First, let’s say you’ve built a custom base image called my-node-base that has Node.js 20 and common npm dependencies pre-installed. Its Dockerfile might look like this:

  FROM node:20-slim
  RUN npm install -g express pm2
  

  Build it with:

  docker build -t my-node-base .
  

• Now, you can build a new application-specific image using this custom base:

  FROM my-node-base
  COPY ./backend-app /app
  WORKDIR /app
  RUN npm install --only=production
  ENTRYPOINT ["pm2-runtime", "start", "app.js"]
  

  Build this new image with:

  docker build -t my-node-backend .
  

This reuses all the pre-built layers from my-node-base, making your build faster and keeping your application Dockerfile focused on your specific code.

2. Can I create Image A on an offline instance using a pre-built Image B from a private registry? #

Yes, this approach works perfectly—you just need to lock in a few key details to make it smooth:

Step-by-Step Solution: #

• 1. Build and prepare Image B on your network-connected local machine
  Create a Dockerfile for Image B that includes every software package, dependency, and configuration your Image A will need (since the target instance is offline, no post-build network installs will be possible). For example:

  FROM debian:bookworm
  # Install all required tools while your local machine has internet
  RUN apt-get update && apt-get install -y --no-install-recommends \
      git vim python3-pip && \
      rm -rf /var/lib/apt/lists/*
  RUN pip3 install flask
  

  Build Image B and tag it for your private registry:

  docker build -t x.x.x.x/B:latest .
  

• 2. Push Image B to your private registry
  First, log your local Docker into the private registry (if authentication is required):

  docker login x.x.x.x
  

  Then push the image:

  docker push x.x.x.x/B:latest
  

• 3. Configure the offline instance to access your private registry
  The offline server must have network connectivity to x.x.x.x (your private registry)—it doesn’t need public internet, just a path to reach the registry. Additionally:

  • If the registry uses self-signed SSL certs, configure Docker on the offline instance to trust those certificates (follow your registry’s documentation for this step).
  • If the registry requires authentication, log into it on the offline instance too:

    docker login x.x.x.x
    

• 4. Write Image A’s Dockerfile on the offline instance
  Your Dockerfile for Image A will use Image B as the base, then add your custom code or configurations. Note: any RUN commands here should not require network access—all dependencies should already be in Image B. Example:

  FROM x.x.x.x/B:latest
  # Copy your application code into the image
  COPY ./flask-app /opt/flask-app
  WORKDIR /opt/flask-app
  ENTRYPOINT ["python3", "app.py"]
  

• 5. Build Image A on the offline instance
  Run the build command—Docker will pull the pre-built Image B layers from your private registry (no public internet needed) and assemble Image A:

  docker build -t image-a .
  

Key Tips: #

• Double-check that Image B includes all dependencies Image A will need—you won’t be able to download new packages on the offline instance.
• Verify the offline instance can resolve and connect to x.x.x.x before starting the build.

内容的提问来源于stack exchange，提问作者Sagar007