168 lines
8.8 KiB
Markdown
168 lines
8.8 KiB
Markdown
# Master节点高可用
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作者：[mendickxiao](https://github.com/mendickxiao)
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经过部署Kubernetes集群章节我们已经可以顺利的部署一个集群用于开发和测试，但是要应用到生产就就不得不考虑master节点的高可用问题，因为现在我们的master节点上的几个服务`kube-apiserver`、`kube-scheduler`和`kube-controller-manager`都是单点的而且都位于同一个节点上，一旦master节点宕机，虽然不应答当前正在运行的应用，将导致kubernetes集群无法变更。本文将引导你创建一个高可用的master节点。
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在大神gzmzj的ansible创建kubernetes集群神作中有讲到如何配置多个Master，但是在实践过程中还是遇到不少坑。需要将坑填上才能工作。
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神作链接地址：[集群规划和基础参数设定](https://github.com/mendickxiao/kubeasz/blob/master/docs/00-%E9%9B%86%E7%BE%A4%E8%A7%84%E5%88%92%E5%92%8C%E5%9F%BA%E7%A1%80%E5%8F%82%E6%95%B0%E8%AE%BE%E5%AE%9A.md)。
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按照神作的描述，实际上是通过keepalived + haproxy实现的，其中keepalived是提供一个VIP，通过VIP关联所有的Master节点；然后haproxy提供端口转发功能。由于VIP还是存在Master的机器上的，默认配置API Server的端口是6443，所以我们需要将另外一个端口关联到这个VIP上，一般用8443。
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根据神作的实践，我发现需要在Master手工安装keepalived, haproxy。
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```bash
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yum install keepalived
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yum install haproxy
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```
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需要将HAProxy默认的配置文件balance从source修改为`roundrobin`方式。haproxy的配置文件`haproxy.cfg`默认路径是`/etc/haproxy/haproxy.cfg`。另外需要手工创建`/run/haproxy`的目录，否则haproxy会启动失败。
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**注意**
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- bind绑定的就是VIP对外的端口号，这里是8443。
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- balance指定的负载均衡方式是`roundrobin`方式，默认是source方式。在我的测试中，source方式不工作。
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- server指定的就是实际的Master节点地址以及真正工作的端口号，这里是6443。有多少台Master就写多少条记录。
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```ini
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# haproxy.cfg sample
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global
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log /dev/log local0
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log /dev/log local1 notice
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chroot /var/lib/haproxy
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*stats socket /run/haproxy/admin.sock mode 660 level admin
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stats timeout 30s
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user haproxy
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group haproxy
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daemon
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nbproc 1
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defaults
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log global
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timeout connect 5000
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timeout client 50000
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timeout server 50000
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listen kube-master
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**bind 0.0.0.0:8443**
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mode tcp
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option tcplog
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**balance roundrobin**
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server s1 **Master 1的IP地址**:6443 check inter 10000 fall 2 rise 2 weight 1
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server s2 **Master 2的IP地址**:6443 check inter 10000 fall 2 rise 2 weight 1
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```
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修改keepalived的配置文件，配置正确的VIP。keepalived的配置文件`keepalived.conf`的默认路径是`/etc/keepalived/keepalived.conf`
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**注意**
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- priority决定哪个Master是主，哪个Master是次。数字大的是主，数字小的是次。数字越大优先级越高。
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- `virtual_router_id`决定当前VIP的路由号，实际上VIP提供了一个虚拟的路由功能，该VIP在同一个子网内必须是唯一。
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- virtual_ipaddress提供的就是VIP的地址，该地址在子网内必须是空闲未必分配的。
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- `state` 决定初始化时节点的状态, 建议 `priority` 最高的节点设置为 `MASTER`。
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```ini
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# keepalived.cfg sample
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global_defs {
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router_id lb-backup
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}
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vrrp_instance VI-kube-master {
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state BACKUP
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**priority 110**
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dont_track_primary
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interface eth0
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**virtual_router_id 51**
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advert_int 3
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virtual_ipaddress {
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**10.86.13.36**
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}
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}
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```
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配置好后，那么先启动主Master的keepalived和haproxy。
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```bash
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systemctl enable keepalived
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systemctl start keepalived
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systemctl enable haproxy
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systemctl start haproxy
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```
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然后使用ip a s命令查看是否有VIP地址分配。如果看到VIP地址已经成功分配在eth0网卡上，说明keepalived启动成功。
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```bash
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[root@kube32 ~]# ip a s
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1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN qlen 1
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link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
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inet 127.0.0.1/8 scope host lo
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valid_lft forever preferred_lft forever
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inet6 ::1/128 scope host
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valid_lft forever preferred_lft forever
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2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000
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link/ether 00:50:56:a9:d5:be brd ff:ff:ff:ff:ff:ff
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inet 10.86.13.32/23 brd 10.86.13.255 scope global eth0
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valid_lft forever preferred_lft forever
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**inet 10.86.13.36/32 scope global eth0**
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valid_lft forever preferred_lft forever
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inet6 fe80::250:56ff:fea9:d5be/64 scope link
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valid_lft forever preferred_lft forever
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```
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更保险方法还可以通过`systemctl status keepalived -l`看看keepalived的状态
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```bash
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[root@kube32 ~]# systemctl status keepalived -l
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● keepalived.service - LVS and VRRP High Availability Monitor
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Loaded: loaded (/usr/lib/systemd/system/keepalived.service; enabled; vendor preset: disabled)
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Active: active (running) since Thu 2018-02-01 10:24:51 CST; 1 months 16 days ago
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Main PID: 13448 (keepalived)
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Memory: 6.0M
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CGroup: /system.slice/keepalived.service
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├─13448 /usr/sbin/keepalived -D
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├─13449 /usr/sbin/keepalived -D
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└─13450 /usr/sbin/keepalived -D
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Mar 20 04:51:15 kube32 Keepalived_vrrp[13450]: VRRP_Instance(VI-kube-master) Dropping received VRRP packet...
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**Mar 20 04:51:18 kube32 Keepalived_vrrp[13450]: (VI-kube-master): ip address associated with VRID 51 not present in MASTER advert : 10.86.13.36
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Mar 20 04:51:18 kube32 Keepalived_vrrp[13450]: bogus VRRP packet received on eth0 !!!**
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```
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然后通过systemctl status haproxy -l看haproxy的状态
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```bash
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[root@kube32 ~]# systemctl status haproxy -l
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● haproxy.service - HAProxy Load Balancer
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Loaded: loaded (/usr/lib/systemd/system/haproxy.service; enabled; vendor preset: disabled)
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Active: active (running) since Thu 2018-02-01 10:33:22 CST; 1 months 16 days ago
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Main PID: 15116 (haproxy-systemd)
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Memory: 3.2M
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CGroup: /system.slice/haproxy.service
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├─15116 /usr/sbin/haproxy-systemd-wrapper -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid
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├─15117 /usr/sbin/haproxy -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid -Ds
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└─15118 /usr/sbin/haproxy -f /etc/haproxy/haproxy.cfg -p /run/haproxy.pid -Ds
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```
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这个时候通过kubectl version命令，可以获取到kubectl的服务器信息。
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```bash
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[root@kube32 ~]# kubectl version
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**Client Version: version.Info{Major:"1", Minor:"9", GitVersion:"v1.9.1", GitCommit:"3a1c9449a956b6026f075fa3134ff92f7d55f812", GitTreeState:"clean", BuildDate:"2018-01-03T22:31:01Z", GoVersion:"go1.9.2", Compiler:"gc", Platform:"linux/amd64"}
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Server Version: version.Info{Major:"1", Minor:"9", GitVersion:"v1.9.1", GitCommit:"3a1c9449a956b6026f075fa3134ff92f7d55f812", GitTreeState:"clean", BuildDate:"2018-01-03T22:18:41Z", GoVersion:"go1.9.2", Compiler:"gc", Platform:"linux/amd64"}**
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```
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这个时候说明你的keepalived和haproxy都是成功的。这个时候你可以依次将你其他Master节点的keepalived和haproxy启动。
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此时，你通过ip a s命令去查看其中一台Master（*非主Master*）的时候，你看不到VIP，这个是正常的，因为VIP永远只在主Master节点上，只有当主Master节点挂掉后，才会切换到其他Master节点上。
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```bash
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[root@kube31 ~]# ip a s
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1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN qlen 1
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link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
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inet 127.0.0.1/8 scope host lo
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valid_lft forever preferred_lft forever
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inet6 ::1/128 scope host
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valid_lft forever preferred_lft forever
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2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000
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link/ether 00:50:56:a9:07:23 brd ff:ff:ff:ff:ff:ff
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inet 10.86.13.31/23 brd 10.86.13.255 scope global eth0
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valid_lft forever preferred_lft forever
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inet6 fe80::250:56ff:fea9:723/64 scope link
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valid_lft forever preferred_lft forever
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```
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在我的实践过程中，通过大神的脚本快速启动多个Master节点，会导致主Master始终获取不了VIP，当时的报错非常奇怪。后来经过我的研究发现，主Master获取VIP是需要时间的，如果多个Master同时启动，会导致冲突。这个不知道是否算是Keepalived的Bug。但是最稳妥的方式还是先启动一台主Master，等VIP确定后再启动其他Master比较靠谱。
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Kubernetes通过Keepalived + Haproxy实现多个Master的高可用部署，你实际上可以采用其他方式，如外部的负载均衡方式。实际上Kubernetes的多个Master是没有主从的，都可以提供一致性服务。Keepalived + Haproxy实际上就是提供了一个简单的负载均衡方式。
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