Question

是否可以通过ACL匹配使用use_backend，但是如果后端不可用（关闭，维护等），则使用默认值？

例如：

    # Define hosts
    acl host_bacon hdr(host) -i ilovebacon.com
    acl host_milkshakes hdr(host) -i bobsmilkshakes.com

    ## figure out which one to use
    use_backend bacon_cluster if host_bacon
    use_backend milshake_cluster if host_milkshakes
    default_backend web-app-cluster

在上述情况下，如果培根和奶昔后端没有可用的服务器，该掉下来并使用web-app-cluster吗？

谢谢

Answer 1

是的，例如，您可以使用类似以下的内容：

acl host_bacon hdr(host) -i ilovebacon.com
acl host_milkshakes hdr(host) -i bobsmilkshakes.com

# check if bacon & milk ok
acl bacon_cluster_down nbsrv(bacon_cluster) lt 1 
acl milks_cluster_down nbsrv(milshake_cluster) lt 1 

# use default web-app if backon & milk down
use_backend web-app-cluster if bacon_cluster_down
use_backend web-app-cluster if milks_cluster_down

use_backend bacon_cluster if host_bacon
use_backend milshake_cluster if host_milkshakes

default_backend web-app-cluster
...

注意使用nbsrv([<backend>]) : integer

来自docs：

Returns an integer value corresponding to the number of usable servers of
either the current backend or the named backend. This is mostly used with
ACLs but can also be useful when added to logs. This is normally used to
switch to an alternate backend when the number of servers is too low to
to handle some load. It is useful to report a failure when combined with
"monitor fail".

在此HAproxy帖子中查看更多示例：failover and worst case management with HAProxy

HAProxy-use_backend（如果可用）

1 个答案: