Most Used Docker Commands:Interview Question
Pre-Requisite:
Package and run Java application as Docker image
Docker builds images by reading instructions from a Dockerfile. A Dockerfile is a simple text file that contains instructions that can be executed on the command line.
What is Dockerfile?
A Dockerfile is a fundamental building block used when dockerizing your Java applications, and it is how you can create a Docker image that can be used to create the containers you need for automatic builds.
Create a new Dockerfile in helloworld directory and use the following content:
FROM openjdk:latest
COPY target/helloworld-1.0-SNAPSHOT.jar /usr/src/helloworld-1.0-SNAPSHOT.jar
CMD java -cp /usr/src/helloworld-1.0-SNAPSHOT.jar org.examples.java.AppTestNG Interview questions and answersBuild the image:
docker image build -t hello-java:latest .
Run the image:
docker container run hello-java:latest
This displays the output:
Hello World!
This shows the exactly same output that was printed when the Java class was invoked using Java CLI.
Package and run Java Application using Docker Maven Plugin
Docker Maven Plugin allows you to manage Docker images and containers using Maven. It comes with predefined goals:
| Goal | Description |
|---|---|
| Build images |
| Create and start containers |
| Stop and destroy containers |
| Push images to a registry |
| Remove images from local docker host |
| Show container logs |
Complete set of goals are listed at https://github.com/fabric8io/docker-maven-plugin.
Clone the sample code from https://github.com/arun-gupta/docker-java-sample/.
Create the Docker image:
mvn -f docker-java-sample/pom.xml package -Pdocker
This will show an output like:
[INFO] Copying files to /Users/argu/workspaces/docker-java-sample/target/docker/hellojava/build/maven
[INFO] Building tar: /Users/argu/workspaces/docker-java-sample/target/docker/hellojava/tmp/docker-build.tar
[INFO] DOCKER> [hellojava:latest]: Created docker-build.tar in 87 milliseconds
[INFO] DOCKER> [hellojava:latest]: Built image sha256:6f815
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------The list of images can be checked using the command docker image ls | grep hello-java:
hello-java latest ea64a9f5011e 5 seconds ago 643 MBRun the Docker container:
mvn -f docker-java-sample/pom.xml install -Pdocker
This will show an output like:
[INFO] DOCKER> [hellojava:latest]: Start container 30a08791eedb
30a087> Hello World!
[INFO] DOCKER> [hellojava:latest]: Waited on log out 'Hello World!' 510 msThis is similar output when running the Java application using java CLI or the Docker container using docker container run command.
The container is running in the foreground. Use Ctrl + C to interrupt the container and return back to terminal.
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Java Coding Interview Questions and Answers
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Only one change was required in the project to enable Docker packaging and running. A Maven profile is added in pom.xml:
<profiles>
<profile>
<id>docker</id>
<build>
<plugins>
<plugin>
<groupId>io.fabric8</groupId>
<artifactId>docker-maven-plugin</artifactId>
<version>0.22.1</version>
<configuration>
<images>
<image>
<name>hello-java</name>
<build>
<from>openjdk:latest</from>
<assembly>
<descriptorRef>artifact</descriptorRef>
</assembly>
<cmd>java -cp maven/${project.name}-${project.version}.jar org.examples.java.App</cmd>
</build>
<run>
<wait>
<log>Hello World!</log>
</wait>
</run>
</image>
</images>
</configuration>
<executions>
<execution>
<id>docker:build</id>
<phase>package</phase>
<goals>
<goal>build</goal>
</goals>
</execution>
<execution>
<id>docker:start</id>
<phase>install</phase>
<goals>
<goal>start</goal>
<goal>logs</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
</profile>
</profiles>How To Dockerize PostgreSQL ?Special credit to arun gupta*
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