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From "PURVIS, Robert (NHS DIGITAL)" <robert.pur...@nhs.net.INVALID>
Subject RE: Number of Web Applications in one Tomcat
Date Mon, 29 Oct 2018 08:49:35 GMT
We have had a single tomcat with multiple applications (10 or more) for many years (since 2002),
and are now separating them. The main reason being that when one application crashes it can
bring down the whole tomcat (e.g. oom errors).

Robert Purvis
robert.purvis@nhs.net<mailto:robert.purvis@nhs.net>



From: Ahmed, Tarek <tarek.ahmed@dimdi.de>
Sent: 29 October 2018 08:00
To: users@tomcat.apache.org
Subject: Number of Web Applications in one Tomcat


Hi all,

TLDR? Do you deploy one web application per tomcat instance or several?

-----------------------

The long story:

I'd like to sound out your opinion regarding the number of web applications deployed in one
tomcat instance. The reason is, that at my place of work the developers prefer one webapp
per tomcat, the admins would rather have as many webapps as possible in one tomcat instance
(yeah, that's devops at its finest ;-)  ). As a developer I'm probably prejudiced, but the
argument goes as follows:



OPS (one tomcat, many webapps):

- Saves memory (each tomcat has a memory footprint even without a web application running)

- Saves extra file systems for each tomcat (logs, tomcat installation, temp directory)

- Saves nagios monitoring configuration

- Saves separate ports (security considerations)

- Saves work distributing security patches



DEV (one webapp per tomcat)

- Start-up time of "fat tomcats" multiplies, which leads to worsened availablity (e.g., our
fattest tomcat contains 32 web services. It takes 4 minutes to start)

- If one webapp goes haywire, it may crash the rest of them (OOM, no more threads, etc.)

- For bug fixes in one application, you may need to restart the complete tomcat instance.
Auto (re)deploy takes you only so far, since loaded classes may not always be unloaded cleanly,
threads not closed etc. This is not always something that can be solved in your own code,
third party libraries may cause problems, too (we had some issues with quartz and infinispan
here).

- If you ever need to profile your application in production, there is much less noise when
analysing heap, thread dumps, cpu usage etc.

- I might even think there is some improved security if webapps are isolated in several processes
vs. being deployed in one VM (security arguments always work well with OPS :-)  )



So, I want to get away from the one-tomcat-multiple-webapps scenario. One thing I started
doing to subvert this policy is using spring boot with embedded tomcats which is cool in a
lot of ways but not always feasible.

What are your practices? Are there further pros and cons for one way or the other? Thanks
so much for any input,

many greetings,

tarek

--
Tarek Ahmed
Softwareentwicklung

DIMDI
Deutsches Institut für
Medizinische Dokumentation und Information
Waisenhausgasse 36-38a
50676 Köln

Tel.: +49 221 4724-268
Fax: +49 221 4724-444
tarek.ahmed@dimdi.de<mailto:tarek.ahmed@dimdi.de>
www.dimdi.de<https://www.dimdi.de>

[tick]

Das DIMDI unterstützt die Vereinbarkeit von Beruf und Familie und ist entsprechend zertifiziert.


Das DIMDI ist ein Institut im Geschäftsbereich des Bundesministeriums für Gesundheit (BMG).


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