Why is Apache not proxying to Tomcat?

Two things:

1. The redirectPort="8443" attribute for the AJP Connector in Tomcat's server.xml is for SSL connections. Since I'm still working on the basic connection, I haven't enabled SSL yet, so this should be redirectPort="8080"

2. Between the two versions of Tomcat that I'm using, the attribute secretRequired for the AJP Connector was changed from a default of false to a default of true. Since I wasn't sending a password with the proxy connection, it failed. Discovered this when I finally remembered to check the Tomcat logs, too (/var/log/tomcat9/catalina.{date}.log on Ubuntu).

The following AJP config works and allows me to load the webapp reverse-proxied through Apache:

    <Connector protocol="AJP/1.3"
               port="8009"
               redirectPort="8080"
               enableLookups="false"
               URIEncoding="UTF-8"
               secretRequired="false" />