Creating an Event Function Using a Container Image Built with Java

For details about how to use a container image to create and execute an event function, see Creating an Event Function Using a Container Image and Executing the Function. This section describes how to create an image using Java and verify the image locally.

1. Run the following command to create a folder:

   mkdir custom_container_event_example && cd custom_container_event_example

2. Use IntelliJ IDEA to create a Spring Boot project and select Spring Web, as shown in Figure 2.
   Figure 1 Creating a Spring Boot project
   
   Figure 2 Selecting Spring Web
   
3. Use Java to implement an HTTP server demo to process HTTP requests and send responses.

   Additionally create a controller package in the demo and implement a HelloWorld class to handle requests. The code is as follows:

   import org.apache.logging.log4j.LogManager;
   import org.apache.logging.log4j.Logger;
   import org.springframework.web.bind.annotation.RequestMapping;
   import org.springframework.web.bind.annotation.RestController;
   
   
   @RestController
   public class HelloWorld {
       //Create a logger for recording debugging information.
       private static final Logger logger = LogManager.getLogger(HelloWorld.class);
   
       //Process the /init request.
       @RequestMapping("/init")
       public String init() {
           logger.debug("access init");
           return "hello init!!";
       }
   
       // Process the /invoke request.
       @RequestMapping("/invoke")
       public String invoke() {
           logger.debug("access invoke");
           return "hello invoke!!";
       }
   
   }

4. Create a Dockerfile file and replace demoSpringBoot-0.0.1-SNAPSHOT.jar with the compiled JAR package.

   FROM ubuntu:22.04
   
   ENV HOME=/home/paas
   ENV GROUP_ID=1003
   ENV GROUP_NAME=paas_user
   ENV USER_ID=1003
   ENV USER_NAME=paas_user
   
   RUN mkdir -m 550 ${HOME} && groupadd -g ${GROUP_ID} ${GROUP_NAME} && useradd -u ${USER_ID} -g ${GROUP_ID} ${USER_NAME}
   
   RUN apt-get update &&  \
       apt-get install -y --no-install-recommends openjdk-21-jre-headless maven &&  \
       apt-get clean
   
   COPY demoSpringBoot-0.0.1-SNAPSHOT.jar ${HOME}/
   
   RUN chown -R ${USER_ID}:${GROUP_ID} ${HOME}
   RUN chmod -R 775 ${HOME}
   
   USER ${USER_NAME}
   WORKDIR ${HOME}
   EXPOSE 8000
   ENTRYPOINT ["java", "-jar", "-Dfile.encoding=utf-8" ,"/home/paas/demoSpringBoot-0.0.1-SNAPSHOT.jar"]

   Table 1 Parameter description

   Parameter	Description
   FROM	Specifies base image ubuntu:22.04. The base image is mandatory and its value can be changed.
   ENV	Sets environment variables HOME (/home/custom_container), GROUP_NAME and USER_NAME (custom_container), and USER_ID and GROUP_ID (1003). These environment variables are mandatory and their values can be changed.
   RUN	Executes commands. The format is RUN <command>. For example, RUN mkdir -m 550 ${HOME} means to create directory ${HOME} for user ${USER_NAME} during container building.
   COPY	Copies files or directories from the build context to the image. Copy demoSpringBoot-0.0.1-SNAPSHOT.jar to the ${HOME} directory of user ${USER_NAME} in the container.
   USER	Switches to user ${USER_NAME}.
   WORKDIR	Switches the working directory to the ${HOME} directory of user ${USER_NAME}.
   EXPOSE	Expose port 8000 of the container. Do not change it.
   ENTRYPOINT	Sets the executable command that is run each time a container starts. Run the following command to start a container: java -jar -Dfile.encoding=utf-8 /home/paas/demoSpringBoot-0.0.1-SNAPSHOT.jar

5. Run the following command to build an image:

   docker build -t custom_container_event_example:latest .

   In the preceding command, the image name is custom_container_event_example, the tag is latest, and the period (.) indicates the directory where the Dockerfile is located. Run the image build command to pack all files in the directory and send the package to a container engine to build an image.