Can you explain the concept of multi-stage builds in Docker and why they are useful?

Multi-layer builds in Docker allow creating images from multiple layers, where each layer represents the result of executing a Dockerfile instruction (e.g., COPY, RUN).

Why is this needed:

• Caching: If a layer hasn't changed, Docker uses the cached version, speeding up the build.
• Size optimization: Layers can be reused across different images.
• Change management: Changes in one layer do not require rebuilding all subsequent layers.

Example:

FROM openjdk:11
COPY pom.xml /app/
RUN mvn dependency:resolve
COPY src/ /app/src/
RUN mvn package

Here, dependency layers are cached, and only source code changes do not require re-downloading dependencies.

Thus, multi-layer builds make the image creation process more efficient and manageable.