Advantages of dockerizing Java Springboot application?

Question

We are working with a dockerized kafka environment. I would like to know the best practices for deployments of kafka-connectors and kafka-streams applications in such scenerio . Currently we are deploying each connector and stream as springboot applications and are started as systemctl microservices . I do not find a significant advantage in dockerizing each kafka connector and stream . Please provide me insights on the same

Answer 1

To me the Docker vs non-Docker thing comes down to "what does your operations team or organization support?"

Dockerized applications have an advantage in that they all look / act the same: you docker run a Java app the same way as you docker run a Ruby app. Where as with an approach of running programs with systemd, there's not usually a common abstraction layer around "how do I run this thing?"

Dockerized applications may also abstract some small operational details, like port management for example - ie making sure all your app's management.ports don't clash with each other. An application in a Docker container will run as one port inside the container, and you can expose that port as some other number outside. (either random, or one to your choosing).

Depending on the infrastructure support, a normal Docker scheduler may auto-scale a service when that service reaches some capacity. However, in Kafka streams applications the concurrency is limited by the number of partitions in the Kafka topics, so scaling up will just mean some consumers in your consumer groups go idle (if there's more than the number of partitions).

But it also adds complications: if you use RocksDB as your local store, you'll likely want to persist that outside the (disposable, and maybe read only!) container. So you'll need to figure out how to do volume persistence, operationally / organizationally. With plain ol' Jars with Systemd... well you always have the hard drive, and if the server crashes either it will restart (physical machine) or hopefully it will be restored by some instance block storage thing.

By this I mean to say: that kstream apps are not stateless, web apps where auto-scaling will always give you some more power, and that serves HTTP traffic. The people making these decisions at an organization or operations level may not fully know this. Then again, hey if everyone writes Docker stuff then the organization / operations team "just" have some Docker scheduler clusters (like a Kubernetes cluster, or Amazon ECS cluster) to manage, and don't have to manage VMs as directly anymore.

Answer 2

Dockerizing + clustering with kubernetes provide many benefits like auto healing, auto horizontal scaling.

Auto healing: in case spring application crashes, kubernetes will automatically run another instances and will ensure required number of containers are always up.

Auto horizontal scaling: if you get burst of messages, yo can tune spring applications to auto scale up or down using HPA that can use custom metrics also.