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13.1.5 pg 260

One thing is to have a hard drop-dead date for the old service otherwise you'll find yourself extending the life of the old service because there will always be someone who is too busy/too important/too arseholeish to be switched and you'll end up running new and old services in parallel forever

13.2.1 pg 264

(Actually this may be more relevant in 11.2.6 pg 226 but I didn't have much to say about this chapter, so I'll write it here :-)) The symlink approach to roll-back works well, but it doesn't allow parallel running if the systems are configured to access files via the symlink. eg if you have /opt/apache.1.2.3 and /opt/apache.1.3.6 and both are configured to use /opt/apache then only one can run at a time.

What we do is have /opt/apache/1.2.3 and /opt/apache/1.3.6 and both are configured to use those paths. We also have /opt/apache/current as a symlink so startup scripts or user commands or whatever can use /opt/apache/current/bin/apachectl etc etc and get the live version, but parallel running is always possible by the "real" path. (In fact we have something even more complicated than that, but I shouldn't describe it since it's home-grown tools quite prevalent in this company and may consititute company-secret).

-- StephenHarris - 17 Aug 2006