Параметр virtual_server.lvs_sched в keepalived.conf поддерживает два варианта, для которых я не могу найти объяснения: fo и md.
Кто-нибудь знает их значение?
Допустимые значения virtual_server.lvs_sched - это имена планировщиков IPVS (IP Virtual Server). Keepalived страница руководства упоминает rr|wrr|lc|wlc|lblc|sh|mh|dh|fo|ovf|lblcr|sed|nq как поддерживаемые имена для планировщиков, это немного больше, чем описано в исходной документации IPVS.
Мне пришлось взглянуть на исходники ядра чтобы увидеть, что это за новые планировщики:
fo "Weighted Fail Over" - все остальные модули планирования реализуют некоторую форму балансировки нагрузки, в то время как это предлагает простое решение для аварийного переключения. Алгоритм взвешенного планирования переключения при отказе направляет сетевые подключения к серверу с наивысшим доступным в настоящее время весом.
Источник: https://patchwork.ozlabs.org/patch/390597/
mh такое "Маглев Хеширование"
/* 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.
*
Алгоритм подробно описан в: 3.4 Последовательное хеширование
Для полноты из ipvasdm страница руководства предоставляет описания других планировщиков:
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.