Service Discovery In Kubernetes
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The document presents an overview of service discovery in Kubernetes, detailing its importance, types, and how it functions. It outlines Kubernetes as an orchestration engine, explaining services as logical sets of pods that facilitate inter-pod communication, and describes service types like NodePort and LoadBalancer. Additionally, it covers methods for service discovery including DNS and environment variables, highlighting the roles of components like kube-dns and CoreDNS.
Service Discovery In Kubernetes
- 1. Presented By: Shubhrank Rastogi & Azmat Hasan Service Discovery in Kubernetes
- 2. Agenda 01 ● A little about K8 ● Service Overview ○ Why do we need them? ○ What is a service? ○ Types of services ● Communication is important - Service Discovery ○ The Scenario ○ Ways to discover services ● Demo
- 3. Quick Overview - About K8 ● Kubernetes (commonly stylized as k8) is an open-source container- orchestration engine for automating application deployment, scaling, and management ● It provides features like deployment, scaling, load balancing, logging, and monitoring ● Designed by Google, and is now maintained by the Cloud Native Computing Foundation (CNCF) ● Master-Slave Architecture ● Kubernetes Objects
- 4. Why do we need services? ● How does this frontend application is exposed to outside world? ● How does frontend application is connected to backend ? ● How do we resolve Pod IP changes, when they die?
- 5. What is a service? ● A Service in Kubernetes is an object, similar to a Pod ● A service can be defined as a logical set of pods ● It acts as the intermediary for Pods to talk to each other ● Selectors are used for accessing all the Pods that match a specific Label ● Each Service exposes one of more ports and targetPorts ● The targetPort is mapped to the port exposed by matching Pods Important Features provided by service: ● Load Balancing ● Service Discovery
- 7. Node Port: ● Exposes the service on each Node’s IP at a static port (the NodePort) ● You’ll be able to contact the NodePort service, from outside the cluster, by requesting <NodeIP>:<NodePort> How does this frontend application is exposed to outside world?
- 8. Cluster IP ● Exposes the service on a cluster-internal IP ● Choosing this value makes the service only reachable from within the cluster ● This is the default ServiceType How does frontend application is connected to backend
- 9. Load Balancer ● Exposes the service externally using a cloud provider’s load balancer ● NodePort and ClusterIP services, to which the external load balancer will route, are automatically created ● It will give you a single IP address that will forward all traffic to your service
- 10. The Scenario
- 11. Components of Service Discovery ● Kube-DNS ○ It is also a DNS server which was default cluster DNS, prior to K8s version 1.11 ○ Several containers are used within a single pod: kubedns, dnsmasq, and sidecar. ■kubedns container watches the Kubernetes API and serves DNS records ■dnsmasq provides caching and stub domain support ■sidecar provides metrics and health checks ● CoreDNS ○ It is a flexible, extensible DNS server that can serve as the Kubernetes cluster DNS ○ Maintained by CNCF ○ Written in GOLang ○ Introduce in K8s version 1.11 as a replacement for KubeDNS
- 12. Service Discovery ● For internal service discovery, Kubernetes provides two options: ○ Environment variable: When a new Pod is created, environment variables from older services can be imported. This allows services to talk to each other. ○ DNS: Every service registers to the DNS server, using this, new services can find and talk to other services. Kubernetes provides the kube-DNS and CoreDNS server for this as an add-on resource. ● For external service discovery, Kubernetes provides two options: ○ NodePort: Kubernetes exposes the service through special ports (30000-32767) of the node IP address. ○ Loadbalancer: Kubernetes interacts with the cloud provider to create a load balancer that redirects the traffic to the Pods.
- 13. Service Discovery - DNS ● Kubernetes has a coreDNS addon that exposes the service’s name as a DNS entry ● The DNS server watches Kubernetes API for new Services ● The DNS server creates a set of DNS records for each Service ○ service.namespace.svc.cluster.local ● Similarly it also creates a set of DNS records for each pod in the cluster ○ 10.32.0.125.namespace.pod.cluster.local ● Services can be resolved by the name within the same namespace ○ phpmyadmin.default.svc.cluster.local ● Pods in other namespaces can access the Service by adding the ○ namespace to the DNS path ■phpmyadmin.my-namespace.svc.cluster.local
- 14. Service Discovery - Environment Variables ● Kubernetes injects environment variables for each service and each port exposed by the service ● Major limitation of this approach is that the service should always be created before then any pods ● Containers can use the environment variable to talk to the service endpoint ● For example, if we are exposing a nginx-service, we can locate it using the NGINX_SERVICE_SERVICE_HOST and NGINX_SERVICE_SERVICE_PORT variables ● The easiest way to find out what environment variables are exposed are to exec the env command within a pod:
- 15. REFERENCES: ● https://kubernetes.io/docs/concepts/ ● https://www.youtube.com/user/srinathrchalla1/ ● https://www.digitalocean.com/community/tutorials/an-introduction-to-the-kubernetes-dns-service ● https://kubernetes.io/docs/tasks/administer-cluster/dns-custom-nameservers/ ● http://kubernetesbyexample.com/sd/ ● https://fredjean.net/kubernetes-discovery/
- 16. Thank You :) ANY Questions?