Application Delivery (ADX)

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Contributor
Posts: 39
Registered: ‎05-04-2009

Why do I see log messages related to a maximum amount of connections (max-conn) I have not configured?

Why do I see log messages related to a maximum amount of connections (max-conn) I have not configured? One of my real servers seems to flap up and down very often and the log messages are talking about the fact that the real server reached its maximum amount of connections which seems to be 10 but I have not configured any max-conn values for my real server. What is happening here?

Here are some of the log messages:

July 07 10:57:31 a.b.c.d SI1, L4 server xxx.xxx.xxx.xxx www-001 port 443 is up

July 0710:57:39 a.b.c.dSI1, Server xxx.xxx.xxx.xxxnamed www-001on port 443  has reached max-conn 10

July 0710:57:40 a.b.c.dSI1, L4 server xxx.xxx.xxx.xxxwww-001port 80 is up

July 0710:57:49 a.b.c.dSI1, Server xxx.xxx.xxx.xxxnamed www-001on port 80  has reached max-conn 10

Any ideas?

Super Contributor
Posts: 316
Registered: ‎05-01-2009

Re: Why do I see log messages related to a maximum amount of connections (max-conn) I have not configured?

I have seen this in the past already. This is most probably related to something called slowstart. Have a look at the documentation. Slowstart jumps in as soon as the real server goes down do to a health check problem. The ServerIron is going to allow the server to ramp up initially.

Out of the documentation:

When the ServerIron begins sending client requests to a real server that has recently gone online, it allows the server to ramp up by using the slow-start mechanism. The slow-start mechanism allows a server (or a port on the server) to handle a limited number of connections at first and then gradually handle an increasing number of connections until the maximum is reached.

There is a default slowstart mechanism which applies to all servers that just come online. The real server gets some time to come up to speed this way. Load balancing predictors like least connections would send all incoming request to this server as soon as it comes online without slowstart. A newly available real server does have less connections than the already active ones in most of the cases.

The initial limit for a real server is 10 connections per second for the first 10 seconds.

Have a look at the slowstart chapter in the SLB guide.

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