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From Christopher Schultz <ch...@christopherschultz.net>
Subject Re: Tomcat 5.5.17 migration to 6
Date Fri, 20 Jul 2018 15:33:32 GMT
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David,

On 7/14/18 4:53 PM, David Babooram wrote:
> Alright.
> 
> I guess the thought the process was to upgrade to 6, then 7, 8

Having gone through exactly this process a few years ago (from 4.1 to
5.0 and continuing on up the major-version ladder until I was
current), I can tell you that it was a collossal waste of our time to
do everything incrementally. We have a very conservative test-to-prod
pipeline at $work (where I'm personally responsible for that process)
and so that transition took a few years.

- From experience, I can tell you that going from 5.5 -> 6.0 is exactly
as difficult as it will be to go from 5.5 -> 8.5. I personally
recommend 8.5 over 9.0 due to some potential
backward-incompatibilities you may encounter with 9.0 that don't exist
in 8.5. An eventual migration from 8.5 -> 9.0 should be much less
"scary" and easy for you to do.

Here is exactly what you should do. There are 2 phases.

Phase I - Prep your environment

1. Read the RUNNING.txt file that comes with Tomcat, especially the
section titled "Advanced Configuration - Multiple Tomcat Instances".

2. Split your existing application configuration in Tomcat 5.5. such
that you have a stock, un-altered Tomcat 5.5.x installation as your
CATALINA_HOME and a CATALINA_BASE which contains your
instance-specific configuration to support your application.

3. Make sure you aren't using any deployments from conf/server.xml.
Specifically, there should be no <Context> elements in that file. If
you have them there, there are better ways of doing deployments.[1]

4. Make sure everything still works.

Once you have done this, everything else will be a lot easier.

Phase II - Upgrade to your target version

0. Throw our all your existing Tomcat configuration. Well, almost.

1. Download a copy of 8.5.32 (current as of this writing) and unpack
it into wherever it will eventually go. This will be your new
CATALINA_HOME for your 8.5.x-based service. Don't change anything. Ever.

2. Create a new CATALINA_BASE structure for your 8.5.x-based service.

3. Compare your existing conf/server.xml file to the stock one from
Phase I step 2 above. There shouldn't be really that many changes...
usually just a few <Connector> definitions. Make appropriate similar
changes to a *copy of* the conf/server.xml file that comes with the
stock Tomcat 8.5.32 distribution and put that file into your new
CATALINA_BASE/conf directory.

4. Stop your old 5.5-based service. Start your 8.5-based service.

5. Test everything.

With any luck, you will just be good to go. If you find any problems,
feel free to ask for some help on this list.

For your next upgrade (e.g. 8.5.32 -> 8.5.33), simply do the following:

1. Unpack the new distribution into a NEW directory (e.g.
apache-tomcat-8.5.33/).

2. Stop your 8.5.32-based service.

3. Change CATALINA_HOME to point to the new directory from step 1.

4. Start Tomcat.

Patch-level upgrades should be just that simple every time. Moving
between versions usually requires starting with a fresh
conf/server.xml from the distribution and making modifications similar
to those described in Phase II step 3.

I hope that helps.

- -chris


[1]
https://tomcat.apache.org/tomcat-8.5-doc/config/context.html#Defining_a_
context
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