Docker - Java container doesn't respect memory limits

Question

I've been reading multiple posts regarding limiting the container's JVM memory, nothing has worked so far, I don't know where I am messing up.

I made a simple "Hello World" in Spring Boot, using a REST controller, it has nothing else.

Such app was exported as a WAR file, running it with the Tomcat JDK 11 image, I can also run it using the JDK image with a FatJar but the problem persists either way.

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Expected

Have my Java container not take more than 25 MB memory (for the sake of a number, could be more)

Actual

Such a simple application is taking 200 - 250 MB memory in docker stats

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Dockerfile

FROM tomcat:9.0.30-jdk11-corretto
COPY tomcat.war /usr/local/tomcat/webapps/ROOT.war
CMD ["catalina.sh","run"]

docker-compose.yml

version: '3.7'

services:
    hello:
        build:
            context: .
            dockerfile: Dockerfile
        image: app-test
        environment:
            - JVM_OPTS=-Xms13m -Xmx25m
        ports:
            - 8080:8080

---

I have tried

-Xms13m -Xmx25m

-XX:PermSize=13m -XX:MaxPermSize=25m

Among other flags that I already deleted and forgot about

Answer 1

To restrict memory for docker containers, you need to add following in your docker-compose.yml file

environment:
  - <name>=<value>
deploy:
  resources:
    memory: 256M

Once you add the above code, then containers would be restricted to given memory limit and you can see the result in docker stats output. For more details about the resource restriction refer this docker documentation.

Note : If the container crosses the given memory limit, the kernel will kill the container.

Answer 2

The environment variable that tomcat's catalina.sh script depends on for java options is : JAVA_OPTS. If you change the compose file to use the following env variable , it should work.

environment: - JAVA_OPTS=-Xmx128m -Xms128m

Apart from the fact that 25m seems a way too less memory for a JVM with tomcat running.

Answer 3

Regardless of how little memory you set for JVM heap (-Xmx) there are lots of other types of non-heap memory that JVM uses: Java using much more memory than heap size (or size correctly Docker memory limit) - you need to take that into account.

You can also avoid setting -Xmx altogether and instead leverage -XX:MaxRAMPercentage: Clarification of meaning new JVM memory parameters InitialRAMPercentage and MinRAMPercentage