Comments on: A/B Technique for Web Application Deployment

by: dmitry

Fri, 26 Jan 2007 19:38:48 +0000

what’s the “empty cache” problem? I have a vague feeling for what it is, but would like to read more about it. Any references? thanks.

by: Nikodem

Thu, 25 Jan 2007 17:29:19 +0000

I used similar approach as described in the response to Hani’s question. Instead of A/B Technique it might be called A/B/C Technique.
A - Old version of the web application and old DB schema
B1 - Version of the web app which can handle the old schema and the new schema together with O L D DB schema
B2 - Version of the web app which can handle the old schema and the new schema together with N E W DB schema
C - New web app together with new DB schema.
Many times the DB changes are just extensions to the existing schema and old version of a web app work with it without problems.

by: Creigh

Tue, 23 Jan 2007 06:28:09 +0000

Still, there are things that will have to be duplicated, like static xml xsl (besides dbase schema changes). Im not sure I would want to mantain all that. Besides, my version A is sitting in cvs under an old tag. I think its a good idea and had some similar ideas along the way. I also like the fact that it keeps environments steady. If B fails in a prod environment then you can revert back to A with min impact. I dont know if its worth redesigning our (complex) deployment proccess just for that though.

by: kyle

Mon, 22 Jan 2007 15:29:06 +0000

Good question, Hani. I added a new section to the post to explain this. The short answer is that if the need is there and the budget is there, you can make nearly any kind of upgrade (possibly as a series of steps) without ever turning a whole system off.

by: Hani

Mon, 22 Jan 2007 15:14:12 +0000

This is fine for simple updates where you can have the two versions (a and b) of your application running. What happens if the update to your application actually changes things like your database schema, making running both A and B impossible?