PHP on Linux randomly fails to connect to Microsoft SQL Server 2005

Question

(Not a Linux guru!) At work we have for the past month had a serious issue that we haven't been able to solve. From a server running Ubuntu-Linux we are using PHP to connect to a server running Microsoft SQL Server 2005. This has been working without problems for a long time. At the start of February 2013 we moved the SQL Server machine into the same core network as the Linux-machine, which involved changing IP-address on the Windows-server running SQL Server 2005.

After this operation we've had issues connecting to the SQL Server from this particular Linux-machine. Maybe one out of 1000 connections fails with the following error message:

PHP Warning: mssql_connect(): Unable to connect to server

I'm not aware of any other changes to either of these two servers. We've tried to look at 'everything'.

• FreeTDS
• php.ini adjustments
• IP-address in SQL Server Configuration Manager
• Unlimited number of concurrent connections in SQL Server
• Network and firewall issues (No packet loss during 24 hours)

Any suggestions to how we can pursue error searching for this problem? Any more info anyone would like to know about this setup? It's kinda serious for us since many of our cronjobs fail to execute normally due to this random connection problem.

Rgds, Sven David, Norway

Answer 1

Very difficult to diagnose from an external perspective, however, it feels like a networking issue rather than php/sql config. Presumably, because it's intermittent, it's not mssql functions/extension. Very little is truly random!

Perhaps approach this by writing a script that monitors the servers (both hosts) vital stats - like a heartbeat: IPs, DNS, DHCP?, requests etc and setting it to record anomalies/alert you when any element changes on either host or connect requests fail...

Probably worth posting on other SE sites too - not just Stackoverflow.