Let's create a LoadBalancer Service with Pods underneath, which is what we learned in Chapter 3, Playing with Containers:

# cat aws-service.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      run: nginx
  template:
    metadata:
      labels:
        run: nginx
    spec:
      containers:
        - image: nginx
          name: nginx
          ports:
            - containerPort: 80
---
apiVersion: v1
kind: Service
metadata:
  name: nginx
spec:
  ports:
    - port: 80
      targetPort: 80
  type: LoadBalancer
  selector:
    run: nginx

In the preceding template, we declared one nginx Pod and associated it with the LoadBalancer service. The service will direct the packet to container port 80:

# kubectl create -f aws-service.yaml 
deployment.apps "nginx" created 
service "nginx" created 

Let's describe our nginx Service:

# kubectl describe svc nginx
Name:                     nginx
Namespace:                default
Labels:                   <none>
Annotations:              <none>
Selector:                 run=nginx
Type:                     LoadBalancer
IP:                       100.68.35.30
LoadBalancer Ingress:     a9da4ef1d402211e8b1240ef0c7f25d3-1251329976.us-east-1.elb.amazonaws.com
Port:                     <unset>  80/TCP
TargetPort:               80/TCP
NodePort:                 <unset>  31384/TCP
Endpoints:                100.124.40.196:80,100.99.102.130:80,100.99.102.131:80
Session Affinity:         None
External Traffic Policy:  Cluster
Events:
  Type    Reason                Age   From                Message
  ----    ------                ----  ----                -------
  Normal  EnsuringLoadBalancer  2m    service-controller  Ensuring load balancer
  Normal  EnsuredLoadBalancer   2m    service-controller  Ensured load balancer 

After the service is created, we will find out that the AWS CloudProvider will provision a classic load balancer with the endpoint adb576a05401911e8b1240ef0c7f25d3-1637943008.us-east-1.elb.amazonaws.com. We can check its detailed settings via the aws command-line interface (https://aws.amazon.com/cli/).

The combination of AWS CLI commands is aws [options] <command> <subcommand> [<subcommand> ...] [parameters]. For listing load balancers, we'll use aws elb describe-load-balancers as the major command. Using the --load-balancer-names parameter will filter load balancers by name, and for the --output parameter, you can choose text, JSON, or table:

# aws elb describe-load-balancers --load-balancer-names a9da4ef1d402211e8b1240ef0c7f25d3 --output text
LOADBALANCERDESCRIPTIONS     a9da4ef1d402211e8b1240ef0c7f25d3-1251329976.us-east-1.elb.amazonaws.com Z35SXDOTRQ7X7K 2018-04-14T20:30:45.990Z       a9da4ef1d402211e8b1240ef0c7f25d3-1251329976.us-east-1.elb.amazonaws.com a9da4ef1d402211e8b1240ef0c7f25d3    internet-facing       vpc-07374a7c
AVAILABILITYZONES     us-east-1a
AVAILABILITYZONES     us-east-1b
AVAILABILITYZONES     us-east-1c
HEALTHCHECK   2      10     TCP:31384     5      6
INSTANCES     i-03cafedc27dca591b
INSTANCES     i-060f9d17d9b473074
LISTENER      31384  TCP    80     TCP
SECURITYGROUPS sg-3b4efb72
SOURCESECURITYGROUP   k8s-elb-a9da4ef1d402211e8b1240ef0c7f25d3   516726565417
SUBNETS subnet-088f9d27
SUBNETS subnet-e7ec0580
SUBNETS subnet-f38191ae

If we access this ELB endpoint port 80, we'll see the nginx welcome page:

Behind the scene, AWS CloudProvider creates a AWS elastic load balancer and configures its ingress rules and listeners by the Service we just defined. The following is a diagram of how the traffic gets into the Pods:

The external load balancer receives the requests and forwards them to EC2 instances using a round-robin algorithm. For Kubernetes, the traffic gets into the Service via NodePort and starts a Service-to-Pod communication. For more information about external-to-Service and Service-to-Pod communications, you can refer to Chapter 3, Playing with Containers.