This example demonstrates how to use Hystrix circuit breaker and the Ribbon Load Balancing. The circuit breaker which is backed with Ribbon will check regularly if the target service is still alive. If this is not loner the case, then a fall back process will be excuted. In our case, the REST greeting service which is calling the name Service responsible to generate the response message will reply a "fallback message" to the client if the name service is not longer replying.
As the Ribbon Kubernetes client is configured within this example, it will fetch from the Kubernetes API Server, the list of the endpoints available for the name service and loadbalance the request between the IP addresses available
This project example runs on ALL the Kubernetes or OpenShift environments, but for development purposes you can use Minishift - OpenShift or Minikube - Kubernetes tool to install the platform locally within a virtual machine managed by VirtualBox, Xhyve or KVM, with no fuss.
First, create a new virtual machine provisioned with Kubernetes on your laptop using the command minikube start.
Next, you can compile your project and generate the Kubernetes resources (yaml files containing the definition of the pod, deployment, build, service and route to be created) like also to deploy the application on Kubernetes in one maven line :
mvn clean install fabric8:deploy -Dfabric8.generator.from=fabric8/java-jboss-openjdk8-jdk -Pkubernetes
When maven has finished to compile the code but also to call the platform in order to deploy the yaml files generated and tell to the platform to start the process to build/deploy the docker image and create the containers where the Spring Boot application will run 'greeting-service" and "name-service", you will be able to check if the pods have been created using this command :
kc get pods
If the status of the Spring Boot pod application is running and ready state 1, then you can
get the external address IP/Hostname to be used to call the service from your laptop
minikube service --url greeting-service
and then call the service using the curl client
curl http://IP_OR_HOSTNAME/greeting
to get a response as such
Hello from name-service-1-0dzb4!d
First, scale the number of pods of the name service to 2
kc scale --replicas=2 deployment name-service
Wait a few minutes before to issue the curl request to call the Greeting Service to let the platform to create the new pod.
kc get pods --selector=project=name-service
NAME READY STATUS RESTARTS AGE
name-service-1652024859-fsnfw 1/1 Running 0 33s
name-service-1652024859-wrzjs 1/1 Running 0 6m
If you issue the curl request to access the greeting service, you should see that the message response contains a different id end of the message which corresponds to the name of the pod.
Hello from name-service-1-0ss0r!
As Ribbon will question the Kubernetes API to get, base on the name-service name, the list of IP Addresses assigned to the service as endpoints,
you should see that you will get a response from one of the 2 pods running
kc get endpoints/name-service
NAME ENDPOINTS AGE
name-service 172.17.0.5:8080,172.17.0.6:8080 40m
Here is an example about what you will get
curl http://IP_OR_HOSTNAME/greeting
Hello from name-service-1652024859-hf3xv!
curl http://IP_OR_HOSTNAME/greeting
Hello from name-service-1652024859-426kv!
...
In order to test the circuit breaker and the fallback option, you will scale the name-service to 0 pods as such
kc scale --replicas=0 deployment name-service
and next issue a new curl request to get the response from the greeting service
Hello from Fallback!
First, create a new virtual machine provisioned with OpenShift on your laptop using the command minishift start.
Next, log on to the OpenShift platform and next within your terminal use the oc client to create a project where
we will install the circuit breaker and load balancing application
oc new-project circuit-loadbalancing
When using OpenShift, you must assign the view role to the default service account in the current project in orde to allow our Java Kubernetes Api to access
the API Server :
oc policy add-role-to-user view --serviceaccount=default
You can now compile your project and generate the OpenShift resources (yaml files containing the definition of the pod, deployment, build, service and route to be created) like also to deploy the application on the OpenShift platform in one maven line :
mvn clean install fabric8:deploy -Pkubernetes
When maven has finished to compile the code but also to call the platform in order to deploy the yaml files generated and tell to the platform to start the process to build/deploy the docker image and create the containers where the Spring Boot application will run 'greeting-service" and "name-service", you will be able to check if the pods have been created using this command :
oc get pods --selector=project=greeting-service
If the status of the Spring Boot pod application is running and ready state 1, then you can
get the external address IP/Hostname to be used to call the service from your laptop
oc get route/greeting-service
and then call the service using the curl client
curl http://IP_OR_HOSTNAME/greeting
to get a response as such
Hello from name-service-1-0dzb4!d
First, scale the number of pods of the name service to 2
oc scale --replicas=2 dc name-service
Wait a few minutes before to issue the curl request to call the Greeting Service to let the platform to create the new pod.
oc get pods --selector=project=name-service
NAME READY STATUS RESTARTS AGE
name-service-1-0ss0r 1/1 Running 0 3m
name-service-1-fblp1 1/1 Running 0 36m
If you issue the curl request to access the greeting service, you should see that the message response contains a different id end of the message which corresponds to the name of the pod.
Hello from name-service-1-0ss0r!
As Ribbon will question the Kubernetes API to get, base on the name-service name, the list of IP Addresses assigned to the service as endpoints,
you should see that you will get a different response from one of the 2 pods running
oc get endpoints/name-service
NAME ENDPOINTS AGE
name-service 172.17.0.2:8080,172.17.0.3:8080 40m
Here is an example about what you will get
curl http://IP_OR_HOSTNAME/greeting
Hello from name-service-1-0ss0r!
curl http://IP_OR_HOSTNAME/greeting
Hello from name-service-1-fblp1!
...
In order to test the circuit breaker and the fallback option, you will scale the name-service to 0 pods as such
oc scale --replicas=0 dc name-service
and next issue a new curl request to get the response from the greeting service
Hello from Fallback!