使用 kube-proxy 进行负载均衡

Question

The official kubernetes docs clearly state that kube-proxy "will not scale to very large clusters with thousands of Services" , however when a LoadBalancer type Service is created on GKE the externalTrafficPolicy is set to Cluster by default (meaning that each request will be load-balanced by kube-proxy anyway in addition to external load balancing). As it is explained for example in this video from Next '17 , this is to avoid traffic imbalance (as Google's external load balancers are not capable of asking a cluster how many pods of a given service are on each node).

Hence the question: does it mean that:

a) by default GKE cannot be used for for "very large clusters with thousands of Services" and to do so I need to risk traffic imbalances by setting externalTrafficPolicy to Local

b) ...or the information about poor scalability of kube-proxy is incorrect or outdated

c) ...or something else that I couldn't come up with

Thanks!

Answer 1

will not scale to very large clusters with thousands of services quote refers to userspace proxy, which was the default mode long time ago before full iptables based implementation happened. So this statement is largely outdated, but...

iptables mode has it's own issues that come with scale (extreamly large iptables rule chains take a lot of time to update) which is one of the reasons why IPVS work made it into kube-proxy. You'd have to have a really hardcore scale to run into performance issues with kube-proxy.

Answer 2

According to the Kubernetes official documentation about externalTrafficPolicy the answer is a).

Since Cluster option obscures the client source IP and may cause a second hop to another node, but should have good overall load-spreading , and Local option preserves the client source IP and avoids a second hop for LoadBalancer and NodePort type services, but risks potentially imbalanced traffic spreading.