Testbed configration: IdPv4 works on Rocky8/JDK 11/Jetty 10/ but not Rocky9/JDK 17/Jetty 11/

[Kevin Buckley]

Having got my Shibboleth testbed going, with a 4.3.1 IdP
deployed on top of

OS:    Rocky 8
JDK:   java-11-openjdk
Jetty: 10

I thought I'd take a look at IdP v5, which came out as I
was creating the testbed.

I noted in the v5 docs that there's a suggestion that one
shouldn't (for now anyway) try and deploy a v5 IdP from
scratch, but upgrade on top of an existing v4 deployment.

However, I also noticed that the v5 requirements were

JDK:   java-17-openjdk
Jetty: 11

so I thought to go back and re-install IdP 4.3.1 on top of

OS:    Rocky 9
JDK:   java-17-openjdk
Jetty: 11

so as to have something viable to upgrade from.

I thought that I had followed the notes I'd made pretty
closely but am seeing, as the Jetty tries to fire up
the IdP WAR-file, the following in its console logging:

...
14:44:47.546 [INFO] :main: (org.eclipse.jetty.deploy.providers.ScanningAppProvider) - Deployment monitor [file:///opt/Jetty/11.0.16/webapps/]
14:44:48.601 [INFO] :main: (org.eclipse.jetty.annotations.AnnotationConfiguration) - Error:  for o.e.j.w.WebAppContext at 58ce9668{idp.xml,/idp,[file:///tmp/jetty-0_0_0_0-8080-idp_war-_idp-any-10475424063315095864/webinf/, jar:file:///opt/shibboleth-idp/war/idp.war!/],STARTING}{/opt/shibboleth-idp/war/idp.war}
14:44:50.998 [WARN] :main: (org.eclipse.jetty.webapp.WebAppContext) - Failed startup of context o.e.j.w.WebAppContext at 58ce9668{Shibboleth Identity Provider,/idp,[file:///tmp/jetty-0_0_0_0-8080-idp_war-_idp-any-10475424063315095864/webinf/, jar:file:///opt/shibboleth-idp/war/idp.war!/],UNAVAILABLE}{/opt/shibboleth-idp/war/idp.war}
java.lang.NoClassDefFoundError: javax/servlet/ServletContextListener
...

In case I am likely to have fallen foul of differences between
the JDK-s or the Jetty-s, or both, or just missed somthing that
I did before, I thought to ask if anyone has any insight or
supposition that might inform what I am seeing?

Kevin Buckley