As I understand tomcat documentation, parallel deployment is intended to be
used to smoothly rollout new versions of webapp. I've looked in source code and
it's written such that there is probably no way to custimize selection of
proper context version. If session is invalid then newest version is always
selected.
I wonder if it would be desirable to build in more flexibility in context
selection process. For example consider following scenario (real one in my
company). We develop complex CRM system and one ROOT.war is used by multiple
customers. Each customer has special ID that has to be part of URL address:
site.com?customer=A
site.com?customer=B
...
All customers A, B, C, ... use the same version 5.x of our app. Now we have
version 6 with massive changes in UI (+external API) and we want to gradually
move our customer base (with their consent) from version 5 to version 6. We
cannot afford to migrate all customers to v6 at once. Giving each of our
customers unique URL (a.site.com, b.site.com, ...) and use virtual hosting is
technically possible but it would complicate other things in our infrastructure.
What I would like to accomplish is to have multiple versions of the app, e.g.:
ROOT##571.war
ROOT##572.war // hotfix of 5.7.1
ROOT##573.war // hotfix of 5.7.2
ROOT##600.war
ROOT##601.war // hotfix of 6.0.0
and two-step process of context version selection.
Step 1)
Belong the request to customer with version 5? -> pre-select ##571,
##572, ##573
Belong the request to customer with version 6? -> pre-select ##600,
##601
Done by my custom ContextVersionSelector interface implementation
(which of coarse would check "customer" param in URI)
Step 2)
Use StandardContextVersionSelector on results from previous step
(current behavior ... it would be used always as last applied selector)
If I understand the code right, all context selection magic is done in
Mapper.java (which is now declared final) and it would have to be modified to
support customizable version selection.
My questions are:
Is there a better way how to accomplish "slow pace" rollout of new version? (I
mean with just Tomcat and nothing more)
If not, do you consider my proposed Mapper imrovement interesting/useful? (I
can try pull request)
Thanks
Tomas
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