This showcase highlights the following key concepts for deploying Spring Boot applications to a Kubernetes cluster:
- Creating docker images for Spring Boot applications using the Jib Maven plugin
- Integration of Spring Boot with Kubernetes using Spring Cloud Kubernetes
- Dynamic configuration for Spring Boot with ConfigMaps.
- Readiness/Liveness Probes backed by Spring Boot health actuator.
- Service lookup with Spring Boot's Feign client and Kubernetes service objects.
- Service discovery with Spring Boot's discovery client.
- Monitoring of Spring Boot applications with Spring Boot Admin.
- Centralized and structured logging for Spring Boot apps using a JSON logback appender.
- Metrics scraping backed by Spring Boot's Micrometer/Prometheus implementation.
- How to use visualization tools to analyze logs and metrics.
After completing the installation described below, you will control a complete application stack with two Spring Boot applications, a logging stack based on fluentd/ElasticSearch/Kibana, a monitoring stack with Prometheus/Grafana and a Spring Boot Admin application.
This guide assumes that you have VirtualBox installed on your computer or a similar virtualization software. Install minikube on your local machine. Create a cluster with the following parameters:
minikube start -p k8s-showcase --memory='8192mb' --disk-size='16384mb' --vm-driver=virtualbox
You should see an output like this:
* Creating virtualbox VM (CPUs=2, Memory=8192MB, Disk=16384MB) ...
* Preparing Kubernetes v1.18.0 on Docker 19.03.8 ...
* Enabling addons: default-storageclass, storage-provisioner
* Done! kubectl is now configured to use "k8s-showcase"
Make sure that k8s-showcase is your current minikube profile. Execute minikube profile k8s-showcase and then verify the current profile with minikube profile.
You should see * k8s-showcase as confirmation.
The Kubernetes Dashboard is very useful when it comes to to track and monitor what is happening your cluster. Open a new command window or shell and start the Kubernetes Dashbord with minikube dashboard. This will open your Browser showing the inital Dashboard screen.
Next check the IP address which is assigned to your cluster with minikube ip. You will get a response like 192.168.99.104. Keep this IP address in mind or even better add it as host name k8s-showcase to C:\Windows\System32\drivers\etc\hosts (You need admin permission to do this). You will need it later to access the apps running inside the cluster.
You can install the full application stack at once. Navigate to the top level directory of the Git project and execute:
kubectl apply -f k8s-deployment
This will apply all deployment files (*.k8s.yml) in the k8s-deployment directory on your Minikube cluster. You should see the following output:
namespace/k8s-spring-boot-apps created
namespace/k8s-logging created
namespace/k8s-monitoring created
persistentvolume/pv0001 created
service/elasticsearch created
statefulset.apps/es-cluster created
serviceaccount/fluentd created
clusterrole.rbac.authorization.k8s.io/fluentd created
clusterrolebinding.rbac.authorization.k8s.io/fluentd created
configmap/fluentd-config created
daemonset.apps/fluentd created
persistentvolumeclaim/grafana-storage created
deployment.apps/grafana created
service/grafana created
service/kibana created
deployment.apps/kibana created
service/kibana configured
clusterrole.rbac.authorization.k8s.io/prometheus created
clusterrolebinding.rbac.authorization.k8s.io/prometheus created
configmap/prometheus-server-conf created
deployment.apps/prometheus created
service/prometheus created
clusterrolebinding.rbac.authorization.k8s.io/admin-default created
configmap/k8s-be created
deployment.apps/k8s-be created
service/k8s-be created
service/k8s-be-management created
deployment.apps/k8s-bff created
service/k8s-bff created
service/k8s-bff-management created
configmap/k8s-sba created
deployment.apps/k8s-sba created
service/k8s-sba created
service/k8s-sba-management created
After a few minutes the cluster should have started all pods. Check the dashboard that everything is green.
You can now visit the installed apps by using the following links: (The hostname k8s-showcase should point to your cluster ip address)
| URL | Description |
|---|---|
| http://k8s-showcase:30001?name=Max | Request to the backend (k8s-be). This will return a simmple message. It will also generate log message |
| http://k8s-showcase:30002?name=Max | Request to the backend-for-frontend (k8s-bff). This will query the backend for a message and return it. |
| http://k8s-showcase:30003 | Opens the Spring Boot Admin UI |
| http://k8s-showcase:30004 | Opens the Kibana UI |
| http://k8s-showcase:30005 | Opens the Prometheus Admin UI |
| http://k8s-showcase:30006 | Opens the Grafana UI (Use admin/admin for first login) |
The backend is a simple REST service which will return the message "Message in a bottle" upon request. You can provide a name as parameter. The message text is configured as Kubernetes ConfigMap and can be changed without a restart. This is achieved using Spring Cloud Kubernetes and Spring Boot's @RefreshScope annotation. (See deployment file spring-boot-apps.k8s.yml)
Calling this service will also produce log and metrics data which can be analyzed later.
The backend-for-frontend uses a Feign Client which queries the backend for messages. The Feign Client is annotated with @FeignClient(url = "http://k8s-be") and automatically finds the backend with the service object's name k8s-be
Both Spring Boot applications provide a full set of actuator endpoints which will be used by the following monitoring tools.
The Spring Boot Admin application is used to gather build, configuration and health status information of the Spring Boot apps. It uses the discovery client provided with Spring Cloud Kubernetes and scans the Kubernetes API for service objects with the label sba-monitored: "true".
Kibana is a powerful tool to analyze data provided by ElasticSearch. As first step you must make the log index available for searching: Select Discover from the menu. Then create an index pattern with fluentd-* and select @timestamp as time field. Now you can search through the logs. Enter kubernetes.labels.app: k8s-be AND level:ERROR as filter and click Refresh. You should see the error log entries created by the Spring Boot app k8s-be.
The log messages produced by the Spring Boot apps are written as JSON to stdout. This is the most efficient way to forward it to the fluentd log daemon, because there is no further parsing required. Additionally, log messages with multiple lines (like the Java stacktrace shown below) do not impose any problems as it might happen with unstructured text output.
Prometheus is a database for storing multi dimensional metrics based on a time line. It is used to scrape the metrics provided by the Spring Boot app's actuators and also by the Kubernetes system components. Open the Prometheus UI and select targets. In the Kubernetes Pods section you should see that Prometheus has detected the Spring Boot apps as scraping targets. This happens automatically because their Kubernetes service object is annotated with appropriate prometheus.io/* values.
With Grafana you can analyze and visualize the data provided by Prometheus and ElasticSearch. First define a datasource for Prometheus using http://prometheus:9090. Now create a dashboard and add chart with the PromQL expression rate(http_server_requests_seconds_count{app="k8s-be"}[1m]). This will give you visualization of HTTP server requests per second for the Spring Boot app k8s-be.
It is also possible to use ElasticSearch as data source: Create a data source using http://elasticsearch.k8s-logging.svc.cluster.local:9200, index-name fluentd-*, pattern no-pattern and version 7.0+. Then add a table to your dashboard and you will see the log messages stored by fluentd to ElasticSearch.
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