There is a lot of optimism around Blue-Green deployments, particularly from luminaries like Martin Fowler.

The challenge with a financial services application, is that to make a blue-green deployment work, you have to guarantee that the old app will still be able to transact whilst the new app is being deployed - which requires testing the old app in light of the new code going in. (Potentially double the testing).

So basically blue-green deployments are infeasible for large financial services applications because you double your regression testing cost just to have extra availability during the release. Instead what you need is a compromise position, where you put the application into 'read-only' mode during the deployment, which reduces risk but still maximises availability.

What some designs do is a 'reporting database' with a web-app read-only mode - so the web app can still work providing information, but not transact.

When I google for this - I can't find this pattern, which makes me think I've got the wrong term.

My question is: What is the DevOps term for 'read-only-deployment' mode of a web application?

closed as primarily opinion-based by gnat, Bart van Ingen Schenau, Kilian Foth, amon, Doc Brown Dec 24 '16 at 12:22

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

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    Not everything is a well-defined pattern. There are some things that don't have "terms." – Robert Harvey Nov 27 '16 at 15:28
  • This actually does have a term, it's "Immutable Deployments". I don't see how it was closed as "opinion based". – Paul Sep 13 '17 at 2:09
  • Thanks Paul - if you have a reference for that then we can get this reopened. – hawkeye Sep 13 '17 at 8:57