1. What Does “Advanced Image Customization” Mean?
Beginner customization is:
- COPY files
- RUN commands
- ADD configs
Advanced customization is:
👉 Improving the image itself 👉 Making it lighter 👉 Making it secure 👉 Making it faster to build 👉 Using multi-stage builds 👉 Removing unnecessary dependencies 👉 Building your own base image
In simple words:
“Build an image that is not just functional, but optimized and production-ready.”
2. Visual Understanding: Lightweight Custom Image
Imagine two images:
Image A: 980 MB (heavy, slow, insecure)
Image B: 18 MB (optimized, fast, safe)
Both run the same app.
Your goal → Build Image B.
Visual:
┌──────────┐ ┌────────────┐
│ Heavy │ vs │ Optimized │
│ Image │ │ Image │
└──────────┘ └────────────┘
Let’s learn how.
3. Customizing Image by Changing Base Image
Your base image decides:
- Size
- Speed
- Security
Example difference:
FROM ubuntu:22.04 → ~200 MB
FROM alpine:3.19 → ~7 MB
Beginner mistake:
FROM ubuntu
Optimized version:
FROM alpine
Same app → 20x smaller image.
4. Add Only What You Need (Minimalist Rule)
Beginner:
RUN apk add --no-cache curl python git build-base vim
Advanced:
RUN apk add --no-cache curl
Install only essential tools. Every unnecessary package = bigger image + bigger attack surface.
5. Multi-Stage Builds — The Most Powerful Customization
This is how large companies reduce 900MB → 25MB.
Example: Node.js App (Advanced Optimization)
# Stage 1: Builder
FROM node:18 AS build
WORKDIR /app
COPY package*.json ./
RUN npm install --production=false
COPY . .
RUN npm run build
# Stage 2: Production Image
FROM node:18-alpine
WORKDIR /app
COPY --from=build /app/dist ./dist
COPY package*.json ./
RUN npm install --production
CMD ["node", "dist/main.js"]
Visual Breakdown:
Stage 1 (builder):
- Full Node image
- Install dev deps
- Build app
---------------------------
Stage 2 (production):
- Tiny Alpine image
- Only production deps
- Only final build output
Result:
Before: 1.1 GB
After: 40 MB
That’s advanced customization.
6. Adding Security Layers to Your Image
✔ Create non-root user
RUN adduser -D appuser
USER appuser
✔ Restrict file permissions
RUN chmod -R 755 /app
✔ Remove temporary files
RUN rm -rf /var/cache/apk/*
These steps make containers safer and smaller.
🧹 7. Clean Up Layers (Reduce Size)
Combine RUN commands:
❌ Beginner style:
RUN apk update
RUN apk add curl
RUN apk add bash
✔ Advanced style:
RUN apk update && apk add curl bash && rm -rf /var/cache/apk/*
Fewer layers → smaller image.
8. Override Config, EntryPoint, Environment
Override entrypoint:
ENTRYPOINT ["node", "server.js"]
Add environment variables:
ENV APP_ENV=production
ENV PORT=3000
Add custom configs:
COPY nginx.conf /etc/nginx/nginx.conf
This is deep customization — controlling runtime behavior.
9. Visual Summary (Advanced Customization Mind Map)
Choose light base image
↓
Install only essential packages
↓
Use multi-stage builds
↓
Remove build tools
↓
Add non-root user
↓
Set configs and entrypoint
↓
Optimize layers
↓
Result: small, secure, production-grade image
Done.
**10. FAQs **
Q1: How do I reduce Docker image size?
Use Alpine, multi-stage builds, and remove unnecessary tools.
Q2: Why is multi-stage build important?
It keeps dev tools out of the final image → smaller, faster, safer.
Q3: Does customizing image affect performance?
Yes — lighter images start faster and deploy faster.
Q4: Should containers run as root?
No. Always create a non-root user for production.
Q5: Can I make my own base image?
Yes — using FROM scratch.
Perfect for Go / Rust static binaries.
🏁 Final Words (Your Tone)
Customizing Docker images is not just about making them work. It’s about making them smart, light, secure, and production-ready.
When you apply these advanced customization steps:
“Your image becomes a professional-grade container that ships fast and runs safely.”
This is next-level Docker mastery.
❤️ At Learn Virendana, we love creating high-quality Docker tutorials that simplify complex concepts and deliver a practical, real-world Docker learning experience for developers