> On 19 Sep 2016, at 23:42, Dmitry Sivachenko <trtrmi...@gmail.com> wrote:
>
> Hello,
>
> imagine the following configuration:
>
> frontend F1
> use_backend BACKUP_B1 if B1_IS_FULL
> default_backend B1
>
> backend B1
> server s_i
> ...
> server s_j
>
> backend BACKUP_B1
> server b_i
> ...
> server b_j
>
> ---------
> frontend F2
> use_backend BACKUP_B2 if B2_IS_FULL
> default_backend B2
>
> backend B2
> server s_k
> ...
> server s_m
>
> backend BACKUP_B2
> server b_k
> ...
> server b_m
> ----------
> <...>
>
> So basically I have a number of backends B1 ... Bn which use different
> subsets of the same server pool s_1 ... s_N.
> Each backend have "BACKUP_" backend pair, which should be used only when each
> server in primary backend has more than a defined number of active sessions
> (each server may have active sessions via different backends: B1, B2, ...,
> Bn).
>
> What is the easiest way to define Bn_IS_FULL acl?
>
> So far I came with the following solution: in each frontend Fn section write:
>
> tcp-request content set-var(sess.s_1_conn) srv_conn(B1/s_1)
> tcp-request content set-var(sess.s_1_conn) srv_conn(B2/s_1),add(sess.s_1_conn)
> # <...> repeat last line for each backend which has s_1. We will have total
> number of active connections to s_1
>
> # Repeat the above block for each server s_2, ..., s_N
>
> #Then define acl, assume the max number of active sessions is 7:
> acl F1_IS_FULL var(sess.s_1_conn) ge 7 var(sess.s_2_conn) ge 7 <...>
>
> but it looks ugly, we need to replicate the same logic in each frontend and
> use a lot of code to count sessions. There should probably be a simpler way
> to track down the total number of active sessions for a server which
> participates in several backends.
>
BTW, it would be convenient to have an ability to have one "super"-backend
containing all servers
backend SUPER_B
server s1
...
server sN
and let other backends reference these servers similar to what we can do with
health checks ("track SUPER_B/s1"):
backend B1
server s_1 SUPER_B/s_1
....
As another benefit this would allow balance algorithm to take into account
connections each server receives via different backends.
