Re: [PATCH] Sloppy TCP, SH rebalancing, SHP scheduling

To: Julian Anastasov <ja@xxxxxx>
Subject: Re: [PATCH] Sloppy TCP, SH rebalancing, SHP scheduling
Cc: lvs-devel@xxxxxxxxxxxxxxx
From: Aleksey Chudov <aleksey.chudov@xxxxxxxxx>
Date: Tue, 28 May 2013 16:41:01 +0300
On 28.05.2013 0:31, Julian Anastasov wrote:
On Fri, 24 May 2013, Aleksey Chudov wrote:

May be better to modify the sync algorithm to synchronize only persistence
templates for these specific cases? Is it possible at all?
        May be, with some flag and also sloppy_tcp. Then the
parametrized SH with netmask will do the same - we can avoid
the sync messages. Of course, with SH there is more risk
for imbalance and it can be exploited. Also SH requires
equal configuration for the real servers.

Currently we are using multiple active / standby server pairs and synchronize them with each other. So half of the servers are constantly doing nothing. We are searching how to use all the servers in active / active mode while maintaining high availability and sessions persistence in case of failure of one of the load balancers. Unfortunately the proposed stateless scheme with SH scheduler and Sloppy TCP is not suitable for as since we are using WLC and WRR schedulers. As you mentioned SH scheduler has several drawbacks because of which we can not use it. Also, we can not synchronize all connections between all servers, since it would require a lot of memory and the search for such a huge connection table is likely to be slower.

But we can solve the sync problem in such a way as done in the conntrackd which allows filtering by flow state. The easiest option is to make the filter only for IP_VS_CONN_F_TEMPLATE state. Thus if all the load balancers will sync persistent templates with each other then even if one of the load balancers fails most users will remain on the same real servers. Of course without the full sync clients must reestablish TCP connections, but for this case we can use Sloppy TCP to create a TCP connection state on any TCP packet.

What do you think of this idea?

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