I have a Java web app running in a Tomcat Server (8080 PORT), my server is linux and it's runing in the 80 port. I have configured the virtual host in apache2, because I want redirect the url, when I write www.domain.com go to www.domain.com:8080/app, my virtual host is:
The Apache webserver has several log files worth examining. The http_access and http_error files are a good start. You can also turn on redirection logging and look at its logfile, although since you are proxying, you probably won't find anything there.
The colors of a "404" page are worth noting as well, since the form of the default 404 page from Tomcat is visually quite different from the default 404 for Apache HTTPD, so that tells you whether the proxying worked.
And, of course, there are the various Tomcat logfiles as well, including the catalina.out and localhost logfiles. Plus you can (and probably should) turn on the access log filter so you can see what the URLs coming into Tomcat look like after the Apache proxy reshapes them.
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