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Kubernetes IPVS和IPTABLES
什么是IPVS
IPVS（IP Virtual Server，IP虚拟服务器）实现了传输层的负载平衡，通常称为4 LAN（四层局域网）交换，是Linux内核的一部分。
IPVS在主机上运行，在真实服务器集群前面充当负载平衡器。IPVS可以将基于 TCP 和 UDP 的服务请求定向到真实服务器上。
IPVS vs IPTABLES
IPVS 模式在 Kubernetes v1.8中引入，在v1.9中成为测试版，在v1.11中成为GA。
IPTABLES模式是在v1.1版本中加入的，从v1.2版本开始成为默认的操作模式。
IPVS和IPTABLES都是基于netfilter的。IPVS模式和IPTABLES模式的区别如下：
-
IPVS为大型集群提供更好的可扩展性和性能。
-
IPVS比IPTABLES支持更复杂的负载平衡算法（最小负载、最小连接、定位、加权等）。
-
IPVS 支持服务器健康检查和连接重试等。
IPVS 对 IPTABLES 的依赖
IPVS代理使用IPTABLES做数据包过滤、SNAT或伪装。具体来说，IPVS代理将使用ipset来存储需要DROP或做伪装的流量的源地址或目的地址，以确保无论我们有多少服务，IPTABLES规则的数量不变。
下面是IPVS代理服务器使用的ipset集的表格。
| set name | members | usage |
|---|---|---|
| KUBE-CLUSTER-IP | All service IP + port | Mark-Masq for cases that masquerade-all=true or clusterCIDR specified |
| KUBE-LOOP-BACK | All service IP + port + IP | masquerade for solving hairpin purpose |
| KUBE-EXTERNAL-IP | service external IP + port | masquerade for packages to external IPs |
| KUBE-LOAD-BALANCER | load balancer ingress IP + port | masquerade for packages to load balancer type service |
| KUBE-LOAD-BALANCER-LOCAL | LB ingress IP + port with externalTrafficPolicy=local
|
accept packages to load balancer with externalTrafficPolicy=local
|
| KUBE-LOAD-BALANCER-FW | load balancer ingress IP + port with loadBalancerSourceRanges
|
package filter for load balancer with loadBalancerSourceRanges specified |
| KUBE-LOAD-BALANCER-SOURCE-CIDR | load balancer ingress IP + port + source CIDR | package filter for load balancer with loadBalancerSourceRanges specified |
| KUBE-NODE-PORT-TCP | nodeport type service TCP port | masquerade for packets to nodePort(TCP) |
| KUBE-NODE-PORT-LOCAL-TCP | nodeport type service TCP port with externalTrafficPolicy=local
|
accept packages to nodeport service with externalTrafficPolicy=local
|
| KUBE-NODE-PORT-UDP | nodeport type service UDP port | masquerade for packets to nodePort(UDP) |
| KUBE-NODE-PORT-LOCAL-UDP | nodeport type service UDP port with externalTrafficPolicy=local
|
accept packages to nodeport service with externalTrafficPolicy=local
|
在以下情况下，IPVS 代理将依赖 IPTABLES。
1. kube-proxy以–masquerade-all=true启动
如果kube-proxy以--masquerade-all=true启动，IPVS代理将伪装所有访问服务集群IP的流量，这与IPTABLES代理的行为相同。假设kube-proxy指定了标志--masquerade-all=true，那么IPVS代理安装的IPTABLES应该如下所示：
# 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-MARK-MASQ (2 references)
target prot opt source destination
MARK all -- 0.0.0.0/0 0.0.0.0/0 MARK or 0x4000
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
MASQUERADE all -- 0.0.0.0/0 0.0.0.0/0 match-set KUBE-LOOP-BACK dst,dst,src
Chain KUBE-SERVICES (2 references)
target prot opt source destination
KUBE-MARK-MASQ all -- 0.0.0.0/0 0.0.0.0/0 match-set KUBE-CLUSTER-IP dst,dst
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 match-set KUBE-CLUSTER-IP dst,dst
2. 在kube-proxy启动时指定集群CIDR
如果kube-proxy以--cluster-cidr=<cidr>启动，IPVS代理将伪装访问服务集群IP的非集群流量，其行为与IPTABLES代理相同。假设kube-proxy提供的集群cidr是10.244.16.0/24，那么IPVS代理安装的IPTABLES应该如下所示。
# 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-MARK-MASQ (3 references)
target prot opt source destination
MARK all -- 0.0.0.0/0 0.0.0.0/0 MARK or 0x4000
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
MASQUERADE all -- 0.0.0.0/0 0.0.0.0/0 match-set KUBE-LOOP-BACK dst,dst,src
Chain KUBE-SERVICES (2 references)
target prot opt source destination
KUBE-MARK-MASQ all -- !10.244.16.0/24 0.0.0.0/0 match-set KUBE-CLUSTER-IP dst,dst
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 match-set KUBE-CLUSTER-IP dst,dst
3. loadBalancer类型的服务
对于loadBalancer类型的服务，IPVS代理将安装IPTABLES与ipset KUBE-LOAD-BALANCER匹配。特别是当服务的LoadBalancerSourceRanges被指定或指定externalTrafficPolicy=local时，IPVS代理将创建ipset集KUBE-LOAD-BALANCER-LOCAL/KUBE-LOAD-BALANCER-FW/KUBE-LOAD-BALANCER-SOURCE-CIDR并相应地安装IPTABLES，它应该看起来像下面所示。
# 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-FIREWALL (1 references)
target prot opt source destination
RETURN all -- 0.0.0.0/0 0.0.0.0/0 match-set KUBE-LOAD-BALANCER-SOURCE-CIDR dst,dst,src
KUBE-MARK-DROP all -- 0.0.0.0/0 0.0.0.0/0
Chain KUBE-LOAD-BALANCER (1 references)
target prot opt source destination
KUBE-FIREWALL all -- 0.0.0.0/0 0.0.0.0/0 match-set KUBE-LOAD-BALANCER-FW dst,dst
RETURN all -- 0.0.0.0/0 0.0.0.0/0 match-set KUBE-LOAD-BALANCER-LOCAL dst,dst
KUBE-MARK-MASQ all -- 0.0.0.0/0 0.0.0.0/0
Chain KUBE-MARK-DROP (1 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 (2 references)
target prot opt source destination
MARK all -- 0.0.0.0/0 0.0.0.0/0 MARK or 0x4000
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
MASQUERADE all -- 0.0.0.0/0 0.0.0.0/0 match-set KUBE-LOOP-BACK dst,dst,src
Chain KUBE-SERVICES (2 references)
target prot opt source destination
KUBE-LOAD-BALANCER all -- 0.0.0.0/0 0.0.0.0/0 match-set KUBE-LOAD-BALANCER dst,dst
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 match-set KUBE-LOAD-BALANCER dst,dst
4. NodePort类型的服务
对于NodePort类型的服务，IPVS代理将安装IPTABLES与ipset KUBE-NODE-PORT-TCP/KUBE-NODE-PORT-UDP的匹配。当指定externalTrafficPolicy=local时，IPVS代理将创建ipset集KUBE-NODE-PORT-LOCAL-TCP/KUBE-NODE-PORT-LOCAL-UDP并相应地安装IPTABLES，这应该是如下所示的：
假设服务的TCP类型为nodePort。
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-MARK-MASQ (2 references)
target prot opt source destination
MARK all -- 0.0.0.0/0 0.0.0.0/0 MARK or 0x4000
Chain KUBE-NODE-PORT (1 references)
target prot opt source destination
RETURN all -- 0.0.0.0/0 0.0.0.0/0 match-set KUBE-NODE-PORT-LOCAL-TCP dst
KUBE-MARK-MASQ all -- 0.0.0.0/0 0.0.0.0/0
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
MASQUERADE all -- 0.0.0.0/0 0.0.0.0/0 match-set KUBE-LOOP-BACK dst,dst,src
Chain KUBE-SERVICES (2 references)
target prot opt source destination
KUBE-NODE-PORT all -- 0.0.0.0/0 0.0.0.0/0 match-set KUBE-NODE-PORT-TCP dst
5. 指定externalIP的服务
对于指定了外部IP的服务，IPVS代理将安装IPTABLES与ipset KUBE-EXTERNAL-IP匹配，假设我们有指定了外部IP的服务，IPTABLES规则应该如下所示：
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-MARK-MASQ (2 references)
target prot opt source destination
MARK all -- 0.0.0.0/0 0.0.0.0/0 MARK or 0x4000
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
MASQUERADE all -- 0.0.0.0/0 0.0.0.0/0 match-set KUBE-LOOP-BACK dst,dst,src
Chain KUBE-SERVICES (2 references)
target prot opt source destination
KUBE-MARK-MASQ all -- 0.0.0.0/0 0.0.0.0/0 match-set KUBE-EXTERNAL-IP dst,dst
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 match-set KUBE-EXTERNAL-IP dst,dst PHYSDEV match ! --physdev-is-in ADDRTYPE match src-type !LOCAL
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 match-set KUBE-EXTERNAL-IP dst,dst ADDRTYPE match dst-type LOCAL
安装IPVS
CentOS
yum install ipset ipvsadm -y
Ubuntu
apt-get install ipset ipvsadm -y
设置
cat > /etc/sysconfig/modules/ipvs.modules <<EOF
#!/bin/bash
modprobe -- ip_vs
modprobe -- ip_vs_rr
modprobe -- ip_vs_wrr
modprobe -- ip_vs_sh
modprobe -- nf_conntrack_ipv4
EOF
chmod 755 /etc/sysconfig/modules/ipvs.modules && bash /etc/sysconfig/modules/ipvs.modules && lsmod | grep -e ip_vs -e nf_conntrack_ipv4
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