keepalived：什麼是 fo 和 mh lvs 調度算法？

keepalived.conf 中的參數virtual_server.lvs_sched支持兩個我找不到解釋的選項： fo和md.

有人知道它們的含義嗎？

允許的值virtual_server.lvs_sched是 IPVS（IP 虛擬伺服器）調度程序的名稱。keepalived手冊頁提到 rr|wrr|lc|wlc|lblc|sh|mh|dh|fo|ovf|lblcr|sed|nq了調度程序的受支持名稱，這比原始 IPVS 文件描述的要多得多。

我不得不看一下核心原始碼，以了解那些較新的調度程序是什麼：

• fo是“加權故障轉移”——所有其他調度模組都實現了某種形式的負載平衡，而這提供了一個簡單的故障轉移解決方案。加權故障轉移調度算法將網路連接定向到目前可用權重最高的伺服器。

來源：https ://patchwork.ozlabs.org/patch/390597/

• mh是“磁懸浮雜湊”

/* The mh algorithm is to assign a preference list of all the lookup
* table positions to each destination and populate the table with
* the most-preferred position of destinations. Then it is to select
* destination with the hash key of source IP address through looking
* up a the lookup table.
*

該算法詳述於：3.4 一致性雜湊

為了完整起見，ipvasdm 手冊頁提供了其他調度程序的描述：

         scheduling-method   Algorithm for allocating TCP connections and
         UDP datagrams to real servers.  Scheduling algorithms are imple-
         mented as kernel modules. Ten are shipped with the Linux Virtual
         Server:

         rr - Robin Robin: distributes jobs equally amongst the available
         real servers.

         wrr - Weighted Round Robin: assigns jobs to real servers propor-
         tionally to there real  servers’  weight.  Servers  with  higher
         weights  receive  new  jobs first and get more jobs than servers
         with lower weights. Servers with equal weights get an equal dis-
         tribution of new jobs.

         lc  -  Least-Connection:  assigns more jobs to real servers with
         fewer active jobs.

         wlc - Weighted Least-Connection: assigns more  jobs  to  servers
         with  fewer  jobs  and  relative  to  the  real  servers’ weight
         (Ci/Wi). This is the default.

         lblc - Locality-Based Least-Connection:  assigns  jobs  destined
         for  the same IP address to the same server if the server is not
         overloaded and available; otherwise assign jobs to servers  with
         fewer jobs, and keep it for future assignment.

         lblcr   -   Locality-Based  Least-Connection  with  Replication:
         assigns jobs destined for the same IP address to the  least-con-
         nection  node  in  the server set for the IP address. If all the
         node in the server set are over loaded, it picks up a node  with
         fewer  jobs  in the cluster and adds it in the sever set for the
         target. If the server set has not been modified for  the  speci-
         fied  time, the most loaded node is removed from the server set,
         in order to avoid high degree of replication.

         dh - Destination Hashing: assigns jobs to servers through  look-
         ing  up a statically assigned hash table by their destination IP
         addresses.

         sh - Source Hashing: assigns jobs to servers through looking  up
         a statically assigned hash table by their source IP addresses.

         sed  -  Shortest  Expected Delay: assigns an incoming job to the
         server with the shortest expected delay. The expected delay that
         the  job  will  experience  is (Ci + 1) / Ui if  sent to the ith
         server, in which Ci is the number of jobs on the the ith  server
         and Ui is the fixed service rate (weight) of the ith server.

         nq  -  Never Queue: assigns an incoming job to an idle server if
         there is, instead of waiting for a fast one; if all the  servers
         are busy, it adopts the Shortest Expected Delay policy to assign
         the job.

引用自：https://serverfault.com/questions/950447