This article represents concepts, revision / quick notes, and practice or sample test/interview questions and answers on Service Discovery topic of Kubernetes. These notes, Q&A could provide to be helpful for those appearing for Kubernetes administrator certification exams (CKA).
Revision Notes – Service Discovery
- Kubernetes supports the following two modes of service discovery:
- Environment variable
- DNS
- Service environment details can be set based on the following format. Service name needs to be in uppercase.
- {SVCNAME}_SERVICE_HOST
- {SVCNAME}_SERVICE_PORT
- When using environment variables for service discovery, it is a mandate that the services must be created prior to the pods which want to access those services.
- DNS server creates a set of records for each service discovered via watching Kubernetes APIs.
- Services of type ExternalName can only be accessed through DNS server.
- For headless service (exposed with a single service IP) not requiring load balancer, the cluster IP (spec.clusterIP)should be specified as None.
- A service can be reached based on the ServiceType assigned to it. The details can be found on this page, Service types
- ClusterIP: The service can be reached from within the cluster
- NodePort: The service can be reached from outside the cluster at the address NodeIP:NodePort. The port is a static port. The request is then routed to appropriate clusterIP service. Note that the clusterIP service gets created automatically. The port number supported must fall in the range, 30000-32767
- LoadBalancer: The service can be reached from the load balancer. The NodePort and ClusterIP services to which request from load balancer will be routed are created automatically.
- ExternalName: The service can be mapped to the content of ExternalName.
- Kubernetes support the notion of the internal load balancer for route traffic from services inside the same VPC. For different cloud providers AWS, Azure or GCP, different configuration annotation need to be applied. Details could be found on this page, internal load balancer
- Kubernetes supports network load balancer starting version 1.9.
Practice Test – Service Discovery
[wp_quiz id=”6192″]
Other Practice Tests / Interview Questions and Answers
- Introduction to Kubernetes
- Pods, Taints and Tolerations
- Container hooks / Pods
- Pod Lifecycle
- Service
References
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I found it very helpful. However the differences are not too understandable for me