Какова роль инструкции FROM в Dockerfile и зачем она необходима?

The FROM instruction in a Dockerfile specifies the base image from which a new image will be built. It is a mandatory directive that defines the starting point for building the container.

Role of FROM:

• Defines the operating system or environment on which your container will run (e.g., ubuntu, alpine, openjdk).
• Allows the use of pre-built images with installed software, which speeds up and simplifies the build process.
• Multiple FROM instructions can be used in a single Dockerfile to create multi-stage builds.

Example:

FROM openjdk:11
COPY . /app
WORKDIR /app
RUN ./gradlew build
CMD ["java", "-jar", "build/libs/app.jar"]

Here, FROM openjdk:11 sets the base image with JDK 11 installed.