Configuring Passthrough Networking for a LoadBalancer Service

Applications

kube-proxy, which is responsible for forwarding intra-cluster traffic, adds the IP addresses of load balancers associated with the LoadBalancer Services to nodes' local forwarding rules by default. When a client from within a cluster accesses the IP address of a load balancer, the traffic is directly forwarded to the destination instead of being forwarded by the load balancer.

Solution

CCE supports passthrough networking. You can configure the kubernetes.io/elb.pass-through annotation for the LoadBalancer Services so that the load balancers forward the intra-cluster access to the IP addresses of the load balancers associated with the Services to their backend pods.

Figure 1 Passthrough networking illustration

• CCE standard clusters

  When a LoadBalancer Service is accessed from within the cluster, traffic is routed to the backend pods using iptables or IPVS by default.

  When a LoadBalancer Service (configured with elb.pass-through) is accessed from within the cluster, traffic is first forwarded to the load balancer, then to the nodes, and finally routed to the backend pods using iptables or IPVS.

Constraints

• This function is only available in clusters v1.19 and later.
• In IPVS, the passthrough settings of Services connected to the same load balancer must be the same.
• If node-level (local) service affinity is used, kubernetes.io/elb.pass-through is automatically set to onlyLocal to enable passthrough networking.

Procedure

This section describes how to create a Deployment using an Nginx image and create a Service with passthrough networking enabled.

1. Use kubectl to access the cluster. For details, see Accessing a Cluster Using kubectl.
2. Use the Nginx image to create a Deployment.

   Create an nginx-deployment.yaml file. The file content is as follows:

   apiVersion: apps/v1     
   kind: Deployment         
   metadata:
     name: nginx            
   spec:
     replicas: 2                     
     selector:              
       matchLabels:
         app: nginx
     template:              
       metadata:
         labels:
           app: nginx
       spec:
         containers:
         - image: nginx:latest
           name: container-0
           resources:
             limits:
               cpu: 100m
               memory: 200Mi
             requests:
               cpu: 100m
               memory: 200Mi
         imagePullSecrets:
         - name: default-secret

   Deploy the workload.

   kubectl create -f nginx-deployment.yaml

3. Create a LoadBalancer Service and set kubernetes.io/elb.pass-through to true.
   The content of the nginx-elb-svc.yaml file is shown below. In this example, a shared load balancer named james is automatically created.

   apiVersion: v1 
   kind: Service 
   metadata: 
     annotations:   
       kubernetes.io/elb.pass-through: "true"
       kubernetes.io/elb.class: union
       kubernetes.io/elb.autocreate: '{"type":"public","bandwidth_name":"cce-bandwidth","bandwidth_chargemode":"bandwidth","bandwidth_size":5,"bandwidth_sharetype":"PER","eip_type":"5_bgp","name":"james"}'
     labels: 
       app: nginx 
     name: nginx 
   spec: 
     externalTrafficPolicy: Local
     ports: 
     - name: service0 
       port: 80
       protocol: TCP 
       targetPort: 80
     selector: 
       app: nginx 
     type: LoadBalancer

4. Create the Service.

   kubectl create -f nginx-elb-svc.yaml

Verification

1. Log in to the ELB console and check the load balancer (named james in this example) associated with the Service.
2. Click the load balancer name and click the Monitoring tab.

   There are 0 connections to the load balancer.

   

3. Log in to an Nginx container in the cluster using kubectl and access the IP address of the load balancer.
   1. Obtain the Nginx containers in the cluster.

      kubectl get pod

      Information similar to the following is displayed:

      NAME                     READY   STATUS    RESTARTS   AGE
      nginx-7c4c5cc6b5-vpncx   1/1     Running   0          9m47s
      nginx-7c4c5cc6b5-xj5wl   1/1     Running   0          9m47s

   2. Log in to an Nginx container.

      kubectl exec -it nginx-7c4c5cc6b5-vpncx -- /bin/sh

   3. Access the load balancer IP address.

      curl **.**.**.**

4. Wait for a while and check the monitoring data on the ELB console.

   If a new access connection is displayed, the load balancer can forward access as expected.