Docker

One service receives the readings of sensors; another one must process and store them. If the first one calls the second one over REST, the two are tied: when the second one is stopped or slow, the first one cannot deliver anything. Kafka sits between them: the first one publishes a message, the second one reads it at its own pace. This post builds that link from end to end, locally: Kafka in KRaft mode in Docker, a Spring Boot service that publishes a plain line of text, another one that reads it, and a page that shows the partition and the offset of each message. All the code is in the tag phase-1 of the public repository iot-monitoring-platform. ...

The pod restarts. kubectl get pod shows OOMKilled, and the exit code is 137. But the logs show no OutOfMemoryError, and the heap was far from full. The JVM did not run out of memory: the container did. The Linux kernel killed the process because it went over its limit. This post shows what the JVM sees in a container, what adds to the heap, how to reproduce the kill, and how to set the memory so that everything fits. All the examples are in the containers/ folder of the public java-gc-lab repository. They use the official eclipse-temurin images: no image to build. ...