Article ID: 113154, created on Jan 14, 2012, last review on Apr 27, 2014

  • Applies to:
  • Operations Automation

Symptoms

Sometimes all sites on Shared Hosting NG server are opened with 503 error.

In Apache error logs on NG server there are records like:

[Thu Oct 20 02:26:39 2011] [error] [client 93.79.240.179] POA VHosts: [pid 232241]Maximum number of connection to 'web.site.com' (12.23.34.45) host has been reached.
[Thu Oct 20 16:27:05 2011] [error] POA VHosts: [pid 398071] Failed to get number of connections to host 'web.site.com' (12.23.34.45) : Wrong shstg session id 1318839119_64510 (should be 1319112903_428549)
[Mon Sep 19 23:27:30 2011] [error] POA VHosts: [pid 201194] Failed to increase number of connections to host 'web.site.com' (12.23.34.45) : Wrong shstg session id 1315894503_8420 (should be 1316460430_204965)
[Mon Sep 19 23:27:30 2011] [error] POA VHosts: [pid 201194] Failed to decrease number of connections to host 'web.site.com' (12.23.34.45) : Wrong shstg session id 1315894503_8420 (should be 1316460430_204965)


Apache restart solves the issue temporarily, and then it appears again.

Limit of simultaneous requests in Service Template of websites subscriptions is set to quite high value (e.g. 50), so the limit is not the reason why all sites can be down due to connection limit exceeding.

Cause

Two shstg_srv processes (NG Caching Service) are run on the web server simultaneously (with different PIDs), they are competing to process Apache requests for website connection counters. This results in counting errors, e.g. connection counter was increased in one shstg session, and attempt to decrease is performed by another shstg session.

Startup script /etc/init.d/shstg is not supposed to allow multiple shstg_srv processes, probably the second instance was started manually avoiding /etc/init.d/shstg.

Resolution

Restart the shstg service on Linux Shared Hosting NG web server:
# service shstg restart

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