How do you approach writing a Docker image build? Where do you get dependency information?

When writing a Docker image build, I start by analyzing the application and its dependencies. Sources of information:

• Dependency management files, such as pom.xml for Maven, build.gradle for Gradle, package.json for Node.js.
• Project documentation and README, where system requirements may be specified.
• Source code to understand which services and libraries are used.

Next, I choose a base image suitable for the stack (for example, openjdk for Java applications). In the Dockerfile, I specify copying the source code, installing dependencies, and building. It is important to minimize the image size and the number of layers.

Example of a simple Dockerfile for Java:

FROM openjdk:17-jdk-slim
WORKDIR /app
COPY target/myapp.jar ./
ENTRYPOINT ["java", "-jar", "myapp.jar"]

Also, I consider that dependencies can be downloaded during the build (for example, via Maven), so in the Dockerfile, I often first copy only the dependency descriptor files, perform the download, and then copy the source code — this speeds up the build when the code changes.