Hazelcast and Docker container

[o haya]

Hi,

Per earlier threads, we have been using Hazelcast caching (and most recently with TCP clustering) with some of our Springboot apps.

We are looking to using Docker containers, and so we are working on running one of our existing Springboot apps, which currently uses Hazelcast for caching (and in some cases, clustering) in a Docker container, and I have some questions:

When being used/integrated with an app, does Hazelcast run as a separate process?  

The reason for this question is that (remember we are new to Docker) we have the impression that it is recommended to run only a single process in a Docker container, and I have done "ps" on the machine where our app is running and I see the app process, but I haven't been able to identify a separate process for Hazelcast?

Additionally, from searching, I saw that there is a Docker image for Hazelcast, and was wondering if we use that, is our app code need to be changed (FYI, we use programmatic configuration for Hazelcast currently) when our app is in a Docker container?

Please advise.

Thanks,

Jim

[Neil Stevenson]

 Hazelcast isn't strictly a process in itself, rather it is a collection of threads that run in a JVM process.

 If you download Hazelcast and use the "start.sh" script, it starts a process that only contains Hazelcast

 If you download the Docker image, https://hub.docker.com/r/hazelcast/hazelcast, it's the same idea, one JVM process containing one Hazelcast

 If you use Spring Boot and you have a HazelcastInstance @Bean, Spring Boot will start this bean and stop the bean as part of the JVM lifecycle.

 In all cases you can add other code and other threads to the JVM, so it'll contain Hazelcast and something else.

 You can even run two or more Hazelcasts in the one JVM process, useful sometimes for testing.

 As a Spring Boot user, you will probably find it easier to let Spring Boot launch your application and Hazelcast -- this would be my personal

recommendation but it's more a matter of choice/preference than any compelling need.

 If you are new to Docker, you will no doubt have a view of Kubernetes as next, and this brings us to configuration.

 

 For code configuration, I (personally) use a @Bean of type "com.hazelcast.config.Config", and in this bean,

check the Spring environment to determine if running in Kubernetes and to use the Kubernetes discovery,

or not and to use the TCP discovery.

 

 TCP discovery works whether you are in Docker or not, but one item that everyone trips on with Docker is networking. Inside the Docker container the process will see

one IP address but from the outside of the container it may differ. Check the system property "hazelcast.local.publicAddress"

which enables a form of NATting.

 There is a guide here https://docs.hazelcast.com/hazelcast/5.0/getting-started/get-started-docker that miight help you get started.

 

 

 Neil

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[Neil Stevenson]

Also, you might find this useful - https://github.com/hazelcast/hazelcast-code-samples/tree/master/hazelcast-integration/kubernetes/samples/springboot-k8s-hello-world

It shows one way to build your own Docker image, and https://github.com/hazelcast/hazelcast-code-samples/blob/master/hazelcast-integration/kubernetes/samples/springboot-k8s-hello-world/the-server/src/main/java/com/hazelcast/samples/kubernetes/ApplicationConfig.java#L64

shows what I mean about letting the environment dictates whether to use TCP or not.

N

[o haya]

Hi,

This is a followup to the information earlier above:

- We have a Springboot application that uses Hazelcast clustering and configures Hazelcat clustering programmatically, and when we build the application in Eclipse

- We want to make a DockerFile that includes both our Springboot application and Hazelcast

- We do not currently use Kubernetes or Kafka (I mention this because some of the examples in docs use Kubernetes or Kafka)

I am trying to determine the approach for doing this, and, in the document https://hub.docker.com/r/hazelcast/hazelcast, there is the "Extending Hazelcast Base Image" section, and in that section, there is this example DockerFile:

FROM hazelcast/hazelcast:$HAZELCAST_VERSION

# Adding custom hazelcast.yaml

ADD hazelcast.yaml ${HZ_HOME}

ENV JAVA_OPTS -Dhazelcast.config=${HZ_HOME}/hazelcast.yaml

 # Adding custom JARs to the classpath

ADD custom-library.jar ${HZ_HOME}

Since we are using programmatic configuration for Hazelcast, if we use the above DockerFile, but without the hazelcast.yml line, i.e.:

FROM hazelcast/hazelcast:$HAZELCAST_VERSION

 # Adding custom JARs to the classpath

ADD our-springboot-app.jar ${HZ_HOME}

would that be sufficient, and could we use that DockerFile to to create our own Docker image, that we could then "run"?

Thanks,

Jim

[Neil Stevenson]

Here's an example

This pom uses `spring-boot-maven-plugin` to form a single bundled jar, then `dockerfile-maven-plugin` to build a docker image that executes that jar

https://github.com/hazelcast/hazelcast-platform-demos/blob/master/telco/churn/hazelcast-node/pom.xml#L85

This is the Dockerfile, which copies the output of the maven compile into the docker image and executes it

https://github.com/hazelcast/hazelcast-platform-demos/blob/master/telco/churn/hazelcast-node/Dockerfile#L19

Does that help?

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[o haya]

Yes, definitely helpful! 

Thanks, and have a great weekend!

Jim