Service
A Service in Kubernetes is an abstraction which defines a logical set of Pods and a policy by which to access them. Services enable a loose coupling between dependent Pods. Services are the abstraction that allow pods to die and replicate in Kubernetes without impacting your application.
The set of Pods targeted by a Service is usually determined by a LabelSelector.
Although each Pod has a unique IP address, those IPs are not exposed outside the cluster without a Service. Services allow your applications to receive traffic. Services can be exposed in different ways by specifying a type
in the ServiceSpec:
ClusterIP (default) - Exposes the Service on an internal IP in the cluster. This type makes the Service only reachable from within the cluster.
NodePort - Exposes the Service on the same port of each selected Node in the cluster using NAT. Makes a Service accessible from outside the cluster using
<NodeIP>:<NodePort>
. Superset of ClusterIP.LoadBalancer - Creates an external load balancer in the current cloud (if supported) and assigns a fixed, external IP to the Service. Superset of NodePort.
ExternalName - Maps the Service to the contents of the
externalName
field (e.g.foo.bar.example.com
), by returning aCNAME
record with its value. No proxying of any kind is set up. This type requires v1.7 or higher ofkube-dns
, or CoreDNS version 0.0.8 or higher.
K8s Service vs Istio Virtual Service
Kubernetes service
Kubernetes service
manages a pod's networking. It specifies whether your pods are exposed internally (ClusterIP
), externally (NodePort
or LoadBalancer
) or as a CNAME of other DNS entries (externalName
).
As an example this foo-service
will expose the pods with label app: foo
. Any requests sent to the node on port 30007
will be forwarded to the pod on port 80
.
Istio virtualservice
Istio virtualservice
is one level higher than Kuberenetes service
. It can be used to apply traffic routing, fault injection, retries and many other configurations to services
.
As an example this foo-retry-virtualservice
will retry 3 times with a timeout 2s each for failed requests to foo
.
Another example of this foo-delay-virtualservice
will apply a 0.5s delay to 0.1% of requests to foo
.
Ref
https://kubernetes.io/docs/concepts/services-networking/service/ https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/ https://istio.io/latest/docs/reference/config/networking/virtual-service/ https://istio.io/latest/docs/concepts/traffic-management/#virtual-services
Service endpoint and endpoint slices
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