Run batch with docker-compose with Java batch

Docker isn't just about launching daemon processes. It is completely ant to launch a batch that is executed only once.

However, starting a container with the docker command is painful. Use docker-compose in batch as well.

This time I would like to run a simple CLI program written in Java as a batch.

Source

https://github.com/knjname/2018-02_DockerComposeBatchExample

You can download from here.

Introduction of composition

Java app part

I made it with Spring boot. Do something like the following: It just prints batch arguments and environment variables.

    //Something like the main function when you bite CommandLineRunner with Spring boot
    @Override
    public void run(String[] args) throws Exception {
		System.out.println("Batch run!!!");
		System.out.println("  args: " + String.join(", ", args));
		System.out.println("  env: " + System.getenv("MY_ENV_VALUE"));
    }

It doesn't matter, but if you want to make something that doesn't matter in Java, use Spring Boot.

Dockerfile part

This is the content to import the JAR built in the previous stage (... AS builder) into the container in the latter half and run the java -jar built JAR.

FROM library/openjdk:9.0.1-11-jre-slim AS builder
ADD . /app
WORKDIR /app
RUN ./gradlew bootRepackage
RUN mv /app/build/libs/*.jar /app.jar

FROM library/openjdk:9.0.1-11-jre-slim
COPY --from=builder /app.jar /app.jar
ENTRYPOINT [ "java", "-jar", "/app.jar" ]

Since the end is ENTRYPOINT, you can pass arguments to the batch.

docker-compose.yml part

For the time being, the environment variables for the batch are given as MY_ENV_VALUE. Actually, I think that it will give the connection destination of the database. In addition, the batch file export directory is also specified here as the volume specification.

`docker-compose.yml`


version: "3.4"

services:

  batch:
    #Docker build the above Docker. -image when built with t myjavabatch:I think it will be something like myjavabatch
    build: ./
    environment:
      MY_ENV_VALUE: "foobarbaz"

# restart:I don't need always
# ports:I don't even need
# network_mode: "host"Even if you specify, there should be no problem unlike daemons.
#It is better to make a batch-only image of Docker instead of using it on the Web.

Find out how to start a batch

As always, don't start as below. This will start the service (daemon).

$ docker-compose up -d

Disposable containers that start when you want to start like a batch are basically started with --rm as shown below.

$ docker-compose run --rm batch batch arguments

By the way, if you can't get a TTY above (such as running from crontab), it won't work. Let's specify -T.

$ docker-compose run --rm -T batch batch arguments

However, there are still traps.

For now (as of 02/06/2018), docker-compose run assigns container names in sequence, such as base name_run_1, but _1 is covered and cannot be started. You may.

Let's explicitly name the container with a random number so that it will not be covered.

$ docker-compose run --rm -T --name `uuidgen`batch batch arguments

This is perfect.

Use ʻuuidgen` command.
It seems that you can prevent double startup by dare to cover the name of the same type of batch, but I will not mention it here.

I also want a trumpet shell

Let's also create a wrapper shell for the above command.

`wrapper.sh`


#!/bin/bash

docker-compose run --rm -T --name `uuidgen` batch "$@"

If you call the batch via the trumpet shell, it's perfect. : smile_cat:

$ ./wrapper.sh my java batch is forever!!

If you want to run it regularly with cron, use crontab -e to define a cron entry like the one below.

`crontab`


# /dev/Don't throw it to null. Systemd for modern OS-Let's give it to cat.
0 * * * * cd /my/path/to/project && ./wrapper.sh my java batch is forever!!! 2>&1 | systemd-cat

in conclusion

Batch execution with docker-compose is nothing special. (I want to believe it is not)

Let's challenge!!