Random Number Generator Service

This repository holds a sample REST service used in most of the examples for the book "Kubernetes Patterns" by Bilgin Ibryam and Roland Huß.

It’s a simple Spring Boot service with a handful of endpoints used to demonstrate Kubernetes concepts.

You can start it locally with with ./mvnw -pl spring spring-boot:run ^[1] and get a random number:

curl -sL http://localhost:8080/ | jq .
{
  "random": 838265052,
  "id": "58da4c5b-ba06-438e-84f8-1a30581baeb8"
}

In order to create a Docker image, just use ./mvnw -pl spring package docker:build. You can easly change the Docker repository and push it to your own account with -Dimage.repo:

./mvnw -Dimage.repo="rhuss" package docker:build push

Configuration

Property	Env Var	Description	Pattern
version	---	Version of this application, created during build	Declarative Deployment
log.file	LOG_FILE	Path to a log file. If set, the write out the generated response values into a CSV file	many
log.url	LOG_URL	If given, send out an HTTP request with the results of a random number generation	Ambassador
build.type	BUILD_TYPE	Add some informations about how the image has been built	Image Builder
pattern	PATTERN	Descriptive label used in environment variables	Envvar Configuration, Configuration Resource
seed	SEED	Seed number to initialize the random number generator. Must be a long.	Configuration Resource

Endpoints

Endpoint	Description	Pattern
/	Return a random number and a unique id of this service	many
/info	Return information about configuration and system	many
/memory-eater	Allocate an array for eating up heap memory. Use parameter "mb" to specify the size in MegaByte	Predictable Demands
/toggle-live	Toggle the status of the Sprint Boot’s actuator health check between UP and DOWN	Health Probe
/toggle-ready	Add or remove the local file which indicates readiness of this service	Health Probe
/shutdown	Shutdown the Spring Boot service	Managed Lifecycle
/logs	Return the content of the logs	Stateful Service, Init Container

Batch

There is also a single class RandomRunner included which creates a list of random numbers into a file:

# Compile stuff first
./mvnw -pl spring compile

# Create a file with 100000 lines in /tmp/random_numbers.txt
java -cp target/classes RandomRunner /tmp/random_numbers.txt 100000

# Write 100000 lines to /dev/random_seed, wait 30s, and then repeat endlessly.
java -c target/classes RandomRunner /dev/random_seed 100000 30

This command is used in the Batch Job and Periodic Job pattern example. The last example is used in Daemon Service pattern example.

Building

Refer to the Image Builder pattern how this example is build from within a Kubernetes cluster.

For creating a tag 2.0 just use the profile -Pv2. This is used for creating images to be used the Declarative Deployment pattern.

Crossbuild the images

In order to compile the images for multiple architectures, use:

docker buildx create --use
docker buildx build --build-arg VERSION="v1" --platform linux/arm64/v8,linux/amd64 -t k8spatterns/random-generator:1.0 .
docker buildx build --build-arg VERSION="v2" --platform linux/arm64/v8,linux/amd64 -t k8spatterns/random-generator:2.0 .

---

1. Instead of the Maven wrapper mvnw you can also use a locally installed mvn