Change:
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. <ins> ## IPVS vs. IPTABLES IPVS mode was introduced in Kubernetes v1.8 and goes beta in v1.9. IPTABLES mode was added in v1.1 and become the default operating mode since v1.2. Both IPVS and IPTABLES are based on `netfilter`. Differences between IPVS mode and IPTABLES mode are as follows: - [IPVS](#ipvs) - [What is IPVS](#what-is-ipvs) - [IPVS vs. IPTABLES](#ipvs-vs-iptables) - [When ipvs falls back to iptables](#when-ipvs-falls-back-to-iptables) - [Run kube-proxy in ipvs mode](#run-kube-proxy-in-ipvs-mode) - [Prerequisite](#prerequisite) - [Local UP Cluster](#local-up-cluster) - [GCE Cluster](#gce-cluster) - [Cluster Created by Kubeadm](#cluster-created-by-kubeadm) - [Debug](#debug) - [Check IPVS proxy rules](#check-ipvs-proxy-rules) - [Why kube-proxy can't start IPVS mode](#why-kube-proxy-cant-start-ipvs-mode) 2. IPVS provides better scalability and performance for large clusters. 3. IPVS supports more sophisticated load balancing algorithms than iptables (least load, least connections, locality, weighted, etc.). 4. IPVS supports server health checking and connection retries, etc. ### When ipvs falls back to iptables IPVS proxier will employ iptables in doing packet filtering, SNAT and supporting NodePort type service. Specifically, ipvs proxier will fall back on iptables in the following 4 scenarios. **1. kube-proxy starts with --masquerade-all=true** If kube-proxy starts with `--masquerade-all=true`, ipvs proxier will masquerade all traffic accessing service Cluster IP, which behaves the same as what iptables proxier. Suppose there is a service with Cluster IP `10.244.5.1` and port `8080`, then the iptables installed by ipvs proxier should be like what is shown below. ```shell # iptables -t nat -nL Chain PREROUTING (policy ACCEPT) target     prot opt source               destination KUBE-SERVICES  all  --  0.0.0.0/0            0.0.0.0/0            /* kubernetes service portals */ Chain OUTPUT (policy ACCEPT) target     prot opt source               destination KUBE-SERVICES  all  --  0.0.0.0/0            0.0.0.0/0            /* kubernetes service portals */ Chain POSTROUTING (policy ACCEPT) target     prot opt source               destination KUBE-POSTROUTING  all  --  0.0.0.0/0            0.0.0.0/0            /* kubernetes postrouting rules */ Chain KUBE-POSTROUTING (1 references) target     prot opt source               destination MASQUERADE  all  --  0.0.0.0/0            0.0.0.0/0            /* kubernetes service traffic requiring SNAT */ mark match 0x4000/0x4000 Chain KUBE-MARK-DROP (0 references) target     prot opt source               destination MARK       all  --  0.0.0.0/0            0.0.0.0/0            MARK or 0x8000 Chain KUBE-MARK-MASQ (6 references) target     prot opt source               destination MARK       all  --  0.0.0.0/0            0.0.0.0/0            MARK or 0x4000 Chain KUBE-SERVICES (2 references) target     prot opt source               destination KUBE-MARK-MASQ  tcp  -- 0.0.0.0/0        10.244.5.1            /* default/foo:http cluster IP */ tcp dpt:8080 ``` **2. Specify cluster CIDR in kube-proxy startup** If kube-proxy starts with `--cluster-cidr=<cidr>`, ipvs proxier will masquerade off-cluster traffic accessing service Cluster IP, which behaves the same as what iptables proxier. Suppose kube-proxy is provided with the cluster cidr `10.244.16.0/24`, and service Cluster IP is `10.244.5.1` and port is `8080`, then the iptables installed by ipvs proxier should be like what is shown below. ```shell # iptables -t nat -nL Chain PREROUTING (policy ACCEPT) target     prot opt source               destination KUBE-SERVICES  all  --  0.0.0.0/0            0.0.0.0/0            /* kubernetes service portals */ Chain OUTPUT (policy ACCEPT) target     prot opt source               destination KUBE-SERVICES  all  --  0.0.0.0/0            0.0.0.0/0            /* kubernetes service portals */ Chain POSTROUTING (policy ACCEPT) target     prot opt source               destination KUBE-POSTROUTING  all  --  0.0.0.0/0            0.0.0.0/0            /* kubernetes postrouting rules */ Chain KUBE-POSTROUTING (1 references) target     prot opt source               destination MASQUERADE  all  --  0.0.0.0/0            0.0.0.0/0            /* kubernetes service traffic requiring SNAT */ mark match 0x4000/0x4000 Chain KUBE-MARK-DROP (0 references) target     prot opt source               destination MARK       all  --  0.0.0.0/0            0.0.0.0/0            MARK or 0x8000 Chain KUBE-MARK-MASQ (6 references) target     prot opt source               destination MARK       all  --  0.0.0.0/0            0.0.0.0/0            MARK or 0x4000 Chain KUBE-SERVICES (2 references) target     prot opt source               destination KUBE-MARK-MASQ  tcp  -- !10.244.16.0/24        10.244.5.1            /* default/foo:http cluster IP */ tcp dpt:8080 ``` **3. Load Balancer Source Ranges is specified for LB type service** When service's `LoadBalancerStatus.ingress.IP` is not empty and service's `LoadBalancerSourceRanges` is specified, ipvs proxier will install iptables which looks like what is shown below. Suppose service's `LoadBalancerStatus.ingress.IP` is `10.96.1.2` and service's `LoadBalancerSourceRanges` is `10.120.2.0/24`. ```shell # iptables -t nat -nL Chain PREROUTING (policy ACCEPT) target     prot opt source               destination KUBE-SERVICES  all  --  0.0.0.0/0            0.0.0.0/0            /* kubernetes service portals */ Chain OUTPUT (policy ACCEPT) target     prot opt source               destination KUBE-SERVICES  all  --  0.0.0.0/0            0.0.0.0/0            /* kubernetes service portals */ Chain POSTROUTING (policy ACCEPT) target     prot opt source               destination KUBE-POSTROUTING  all  --  0.0.0.0/0            0.0.0.0/0            /* kubernetes postrouting rules */ Chain KUBE-POSTROUTING (1 references) target     prot opt source               destination MASQUERADE  all  --  0.0.0.0/0            0.0.0.0/0            /* kubernetes service traffic requiring SNAT */ mark match 0x4000/0x4000 Chain KUBE-MARK-DROP (0 references) target     prot opt source               destination MARK       all  --  0.0.0.0/0            0.0.0.0/0            MARK or 0x8000 Chain KUBE-MARK-MASQ (6 references) target     prot opt source               destination MARK       all  --  0.0.0.0/0            0.0.0.0/0            MARK or 0x4000 Chain KUBE-SERVICES (2 references) target     prot opt source       destination ACCEPT  tcp  -- 10.120.2.0/24    10.96.1.2       /* default/foo:http loadbalancer IP */ tcp dpt:8080 DROP    tcp  -- 0.0.0.0/0        10.96.1.2       /* default/foo:http loadbalancer IP */ tcp dpt:8080 ``` **4. Support NodePort type service** For supporting NodePort type service, ipvs will recruit the existing implementation in iptables proxier. For example, ```shell # kubectl describe svc nginx-service Name:			nginx-service ... Type:			NodePort IP:			    10.101.28.148 Port:			http	3080/TCP NodePort:		http	31604/TCP Endpoints:		172.17.0.2:80 Session Affinity:	None # iptables -t nat -nL [root@100-106-179-225 ~]# iptables -t nat -nL Chain PREROUTING (policy ACCEPT) target     prot opt source               destination KUBE-SERVICES  all  --  0.0.0.0/0            0.0.0.0/0            /* kubernetes service portals */ Chain OUTPUT (policy ACCEPT) target     prot opt source               destination KUBE-SERVICES  all  --  0.0.0.0/0            0.0.0.0/0            /* kubernetes service portals */ Chain KUBE-SERVICES (2 references) target     prot opt source               destination KUBE-MARK-MASQ  tcp  -- !172.16.0.0/16        10.101.28.148        /* default/nginx-service:http cluster IP */ tcp dpt:3080 KUBE-SVC-6IM33IEVEEV7U3GP  tcp  --  0.0.0.0/0            10.101.28.148        /* default/nginx-service:http cluster IP */ tcp dpt:3080 KUBE-NODEPORTS  all  --  0.0.0.0/0            0.0.0.0/0            /* kubernetes service nodeports; NOTE: this must be the last rule in this chain */ ADDRTYPE match dst-type LOCAL Chain KUBE-NODEPORTS (1 references) target     prot opt source               destination KUBE-MARK-MASQ  tcp  --  0.0.0.0/0            0.0.0.0/0            /* default/nginx-service:http */ tcp dpt:31604 KUBE-SVC-6IM33IEVEEV7U3GP  tcp  --  0.0.0.0/0            0.0.0.0/0            /* default/nginx-service:http */ tcp dpt:31604 Chain KUBE-SVC-6IM33IEVEEV7U3GP (2 references) target     prot opt source               destination KUBE-SEP-Q3UCPZ54E6Q2R4UT  all  --  0.0.0.0/0            0.0.0.0/0            /* default/nginx-service:http */ Chain KUBE-SEP-Q3UCPZ54E6Q2R4UT (1 references) target     prot opt source               destination KUBE-MARK-MASQ  all  --  172.17.0.2           0.0.0.0/0            /* default/nginx-service:http */ DNAT       tcp  --  0.0.0.0/0            0.0.0.0/0            /* default/nginx-service:http */ tcp to:172.17.0.2:80 ``` </ins> ## Run kube-proxy in ipvs mode <del> Currently, local-up scripts and kubeadm support switching IPVS proxy mode via exporting environment variables or specifying flags. </del> <ins> Currently, local-up scripts, GCE scripts and kubeadm support switching IPVS proxy mode via exporting environment variables or specifying flags. ### Prerequisite Ensure the following kernel modules required by IPVS-based kube-proxy have been compiled into the node kernel (use `lsmod` to check): ```shell ip_vs ip_vs_rr ip_vs_wrr ip_vs_sh nf_conntrack_ipv4 ``` Packages such as `ipset` should also be installed on the node before using IPVS mode. Kube-proxy will fall back to IPTABLES mode if those requirements are not met. </ins> ### Local UP Cluster Kube-proxy will run in iptables mode by default in a [local-up cluster](https://github.com/kubernetes/community/blob/master/contributors/devel/running-locally.md). <del> Users should export the env `KUBE_PROXY_MODE=ipvs` to specify the ipvs mode before deploying the cluster if want to run kube-proxy in ipvs mode. </del> <ins> To use IPVS mode, users should export the env `KUBE_PROXY_MODE=ipvs` to specify the ipvs mode before [starting the cluster](https://github.com/kubernetes/community/blob/master/contributors/devel/running-locally.md#starting-the-cluster): ```shell #before running `hack/local-up-cluster.sh` export KUBE_PROXY_MODE=ipvs ``` ### GCE Cluster Similar to local-up cluster, kube-proxy in [clusters running on GCE](https://kubernetes.io/docs/getting-started-guides/gce/) run in iptables mode by default. Users need to  export the env `KUBE_PROXY_MODE=ipvs` before [starting a cluster](https://kubernetes.io/docs/getting-started-guides/gce/#starting-a-cluster): ```shell #before running one of the commmands chosen to start a cluster: # curl -sS https://get.k8s.io | bash # wget -q -O - https://get.k8s.io | bash # cluster/kube-up.sh export KUBE_PROXY_MODE=ipvs ``` </ins> ### Cluster Created by Kubeadm Kube-proxy will run in iptables mode by default in a cluster deployed by [kubeadm](https://kubernetes.io/docs/setup/independent/create-cluster-kubeadm/). If you are using kubeadm with a [configuration file](https://kubernetes.io/docs/reference/setup-tools/kubeadm/kubeadm-init/#config-file), you can specify the ipvs mode adding `SupportIPVSProxyMode: true` below the `kubeProxy` field. <del> Then the configuration file is similar to: </del> ```json kind: MasterConfiguration

Discussion:
/kind documentation What happened: IPVS needs to be documented more. Specifically, the existing documentation needs to be updated to properly describe how to bring up a cluster with ipvs in the kubeadm, local and gce case. Furthermore, there needs to be another piece of documentation that describes the main differences between iptables and ipvs and also dives into implementation differences between the two (ex. ipset). It would also be really nice if there could be some screenshots detailing the difference between iptables and ipvs rules (i.e bring up a cluster, create a service, dump iptables and ipvs rules, compare) All this documentation should be to pkg/proxy/ipvs /assign /area ipvs /sig network