Keepalived：僅最高權重調度

我有一個 ip 後面的三台伺服器的 keepalived 設置。一個被設置為sorry server，只為維護頁面提供服務，另外兩個是實際的應用伺服器。我們希望它設置為使流量僅路由到一台伺服器，直到它出現故障，然後讓另一台伺服器接收流量，直到主伺服器重新聯機。

省略 lb_algo 會導致此錯誤並且 keepalived 拒絕啟動

Jan 23 17:15:22 fw001 kernel: IPVS: Scheduler module ip_vs_ not found

lb_algo 的唯一選項是：

rr|wrr|lc|wlc|lblc|sh|dh

所有這些都以某種方式在活動伺服器上進行負載平衡。

配置範例

virtual_server 203.0.113.0 80 {
   delay_loop 60
   lb_algo wrr
   lb_kind NAT
   nat_mask 255.255.255.0
   persistence_timeout 50
   protocol TCP

   sorry_server 10.0.0.3 8080

   real_server 10.0.0.1 8080 {
       weight 100

       HTTP_GET {
           url {
               path /alive
               digest 7a13a825b31584fe9b135ab53974d893
           }
           connect_timeout 30
           nb_get_retry 30
           delay_before_retry 10
       }
   }

   real_server 10.0.0.2 8080 {
       weight 0

       HTTP_GET {
           url {
               path /alive
               digest 7a13a825b31584fe9b135ab53974d893
           }
           connect_timeout 30
           nb_get_retry 30
           delay_before_retry 10
       }
   }
}

有沒有辦法做到這一點？

來自 LVS 郵件列表

None of the current IPVS schedulers do know "highest weight" balancing.

With the "weighted" schedulers, you can e.g. give your primary server 
a weight of max. 65535 and your secondary server a weight of 1. This way,
you've "almost" reached the point you're asking for - however, one out
of 64k of incoming connections will go for the "secondary" server even
while the primary server is still up and running.

If your application is balancing-ready, this behaviour may be a good thing.
For example, by automatically using the secondary system for a few live 
requests, you ensure your secondary system is actually working.
By sending some live traffic, you may also "warm up" application-specific
caches, so upon a "real" failover, the application will perform much better
than with empty caches.

If you really don't need (or your applications can't handle) the 
"balancing" part (distribute traffic to different servers at the same time),
you'd probably better run "typical" high availability/failover software 
like Pacemaker or some VRRP daemon.

For example, you might put all three boxes into the same VRPR instance
and assign them different VRRP priorities, and VRRP will sort out which box 
has the "best" priority and is going to be the only live system. This results
in some kind of "cascading" failover.


If you need balancing to distribute traffic among different servers,
and you'd still like to have this "cascading" failover, you'll need to run 
at least two balancer (pairs): one for the "primary" server farm, with the 
VIP of the other balancer being set as sorry server. The second balancer 
in turn balances to the "secondary" server farm and also has the maintenance 
server set as a sorry server.

One usecase for such scenarios are web farms with slightly different content: 
if the primary farm drops out of service (e.g. due to overload or some
bleeding-edge feature malfunctioning), the secondary farm may serve a less 
feature-rich version of the same service.

引用自：https://serverfault.com/questions/471886