Mark and Aditya,
On 10/18/23 04:21, Mark Thomas wrote:
On 17/10/2023 22:47, Aditya Shastri wrote:
Hello,
We have several tomcat instances that use a single CATALINA_HOME which
is a symlink for a specific version. The Tomcat instance we use is
very barebones and doesn't have any of the apps that come with it.
For example,
The CATALINA_HOME points to a symlink
/opt/tomcat/tomcat-9/tomcat-9-latest ->
/opt/tomcat/tomcat-9/apache-tomcat-9.0.80.
Now, if I want to upgrade to apache-tomcat-9.0.82, I normally do the
following steps:
1. Stop all the running instances of tomcat in the various
'CATALINA_BASE'.
2. Update the symlink /opt/tomcat/tomcat-9/tomcat-9-latest from
/opt/tomcat/tomcat-9/apache-tomcat-9.0.80 to
/opt/tomcat/tomcat-9/apache-tomcat-9.0.82.
3. Start all the instances.
This method appears to work, and I read it as the most appropriate
method.
My question is, can I change the symlink,
'/opt/tomcat/tomcat-9/tomcat-9-latest', while all the instances are
running and restart the instances when I have downtime?
Probably not. You might get away with it sometimes but sometimes you are
going to see errors.
Does Tomcat load all the CATALINA_HOME jar(s) (not including the
webapps folder) and config to memory thereby not caring if the
libraries have changed or does it realize that something has changed?
No. The JVM loads classes when they are first referenced.
The issue will be if you update the symlink, then Tomcat tries to load
another class and the class from the new version is not compatible with
the classes from the old version. A failure is unlikely but not
impossible. I wouldn't risk it.
I wonder if we could solve this, at least on *NIX, by resolving
CATALINA_HOME by using `readlink -f`. This would allow you to use a
symlink to point to Tomcat but after catalina.sh is invoked,
CATALINA_HOME could be replaced with a canonicalized one which does not
contain a symlink anymore. Maybe there is a similar
utility/command/path-mangling-magic available on Windows?
That would allow you to change the symlink and not disturb any
currently-running Tomcat instances. You would obviously not want to
remove the old version from the disk before shutting-down those
instances, of course.
-chris
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