How to use IPVS

This document shows how to use kube-proxy ipvs mode.

What is IPVS

IPVS (IP Virtual Server) implements transport-layer load balancing, usually called Layer 4 LAN switching, as part of Linux kernel.

IPVS runs on a host and acts as a load balancer in front of a cluster of real servers. IPVS can direct requests for TCP and UDP-based services to the real servers, and make services of real servers appear as virtual services on a single IP address.

Run kube-proxy in ipvs mode

Currently, local-up scripts and kubeadm support switching IPVS proxy mode via exporting environment variables or specifying flags.

Local UP Cluster

Kube-proxy will run in iptables mode by default in a local-up cluster.

Users should export the env KUBEPROXY_MODE=ipvs to specify the ipvs mode before deploying the cluster if want to run kube-proxy in ipvs mode.

Cluster Created by Kubeadm

Kube-proxy will run in iptables mode by default in a cluster deployed by kubeadm.

Since IPVS mode is still feature-gated, users should add the flag --feature-gates=SupportIPVSProxyMode=true in kubeadm init command

kubeadm init --feature-gates=SupportIPVSProxyMode=true

to specify the ipvs mode before deploying the cluster if want to run kube-proxy in ipvs mode.

If you are using kubeadm with a configuration file, you can specify the ipvs mode adding SupportIPVSProxyMode: true below the featureGates field. Then the configuration file is similar to:

kind: MasterConfiguration
apiVersion: kubeadm.k8s.io/v1alpha1
...
kubeProxy:
  config:
    featureGates: SupportIPVSProxyMode=true
    mode: ipvs
...

Debug

Check IPVS proxy rules

People can use ipvsadm tool to check whether kube-proxy are maintaining IPVS rules correctly. For example, we may get IPVS proxy rules like:

# ipvsadm -ln
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
TCP  10.0.0.1:443 rr persistent 10800
  -> 10.229.43.2:6443             Masq    1      0          0         
TCP  10.0.0.10:53 rr      
UDP  10.0.0.10:53 rr

Why kube-proxy can't start IPVS mode

People can do the following check list step by step:

1. Enable IPVS feature gateway

Currently IPVS-based kube-proxy is still in alpha phase, people need to enable --feature-gates=SupportIPVSProxyMode=true explicitly.

2. Specify proxy-mode=ipvs

Tell kube-proxy that proxy-mode=ipvs, please.

3. Load ipvs required kernel modules

The following kernel modules are required by IPVS-based kube-proxy:

ip_vs
ip_vs_rr
ip_vs_wrr
ip_vs_sh
nf_conntrack_ipv4

IPVS-based kube-proxy will load them automatically. If it fails to load them, please check whether they are compiled into your kernel.