DevOps Classroom notes 12/Jun/2026

Multi-staged docker image build

• Java:
  • To build java application i might need
    • JDK
    • Maven/Gradle
  • To run the java application i need
    • JRE
• Dotnet:
  • To build dotnet application i need
    • dotnet SDK
  • To run the dotnet application i need
    • dotnet Runtime
• To solve this docker introduced multi staged Docker file
• i.e in Dockerfile i can have multiple stages, only last stage will be your application image
• Example

FROM maven:3-eclipse-temurin-21 AS build
COPY . /app
WORKDIR /app
RUN mvn package


FROM eclipse-temurin:21-jre-alpine 
RUN mkdir /app
COPY --from=build /app/target/spring-petclinic-4.0.0-SNAPSHOT.jar /app
WORKDIR /app
EXPOSE 8080
CMD ["java", "-jar", "spring-petclinic-4.0.0-SNAPSHOT.jar"]

• Try for similar stuff in other languages,
• Exercise: Refer Here and Refer Here for other languages

Securing docker images

• Docker gives docker hardened images (DHI) and there are distroless images