How to deploy a jhipster production website to https? - spring-boot

Question

Please could someone provide clear and working instructions to deploy a jhipster site (created with the most up-to-date version) to a server with the most recent LTS ubuntu.
Please note that I have read the documents https://www.jhipster.tech/production/ and https://www.jhipster.tech/production/#security.
I can change the server port to 443 application-prod.yml, but then I get an undertow error (my understanding is that on a linux server to use the port 443 from an application I would have to use sudo to run the application - I don't want/see why I would do that). I have tried port forwarding (Can zuul be configured to listening to port 80, I'm ok with using sudo for this)
sudo iptables -t nat -I OUTPUT -p tcp -d 127.0.0.1 --dport 443 -j REDIRECT --to-ports 8080
but this does not achieve the desired result.
I can access the website through https://111.1.1.1:8080 (not the real ip address), https://mywebsitename.com:8080 (but get self certification issues in the browser [firefox]). I have tried to create an external certificate using the jhipster instructions, but with no success. The jhipster site has 404's or the recommendations given to achieve this have no installation candidate.
How can I set up my jhipster application/server to get the address of the site to be https://mywebsitename.com without errors? Are there any working, up-to-date guides/tutorials I can follow?
edit 1:
Changing the port number to 443 in application-prod.yml gives the error when trying to run:
2020-10-14 16:10:38.151 ERROR 9574 --- [ main] o.s.boot.SpringApplication : Application run failed
org.springframework.boot.web.server.WebServerException: Unable to start embedded Undertow
at org.springframework.boot.web.embedded.undertow.UndertowServletWebServer.start(UndertowServletWebServer.java:155)
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.startWebServer(ServletWebServerApplicationContext.java:297)
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.finishRefresh(ServletWebServerApplicationContext.java:163)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:553)
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:315)
at com.mywebsitename.MywebsitenameApp.main(MywebsitenameApp.java:63)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.springframework.boot.loader.MainMethodRunner.run(MainMethodRunner.java:48)
at org.springframework.boot.loader.Launcher.launch(Launcher.java:87)
at org.springframework.boot.loader.Launcher.launch(Launcher.java:51)
at org.springframework.boot.loader.JarLauncher.main(JarLauncher.java:52) Caused by: java.lang.RuntimeException: java.net.SocketException: Permission denied
at io.undertow.Undertow.start(Undertow.java:247)
at org.springframework.boot.web.embedded.undertow.UndertowServletWebServer.start(UndertowServletWebServer.java:141)
... 16 common frames omitted Caused by: java.net.SocketException: Permission denied
at java.base/sun.nio.ch.Net.bind0(Native Method)
at java.base/sun.nio.ch.Net.bind(Net.java:455)
at java.base/sun.nio.ch.Net.bind(Net.java:447)
at java.base/sun.nio.ch.ServerSocketChannelImpl.bind(ServerSocketChannelImpl.java:227)
at java.base/sun.nio.ch.ServerSocketAdaptor.bind(ServerSocketAdaptor.java:80)
at org.xnio.nio.NioXnioWorker.createTcpConnectionServer(NioXnioWorker.java:190)
at org.xnio.XnioWorker.createStreamConnectionServer(XnioWorker.java:243)
at io.undertow.protocols.ssl.UndertowXnioSsl.createSslConnectionServer(UndertowXnioSsl.java:411)
at io.undertow.Undertow.start(Undertow.java:232)
... 17 common frames omitted
This is without and with including provided for undertow in pom.xml, as detailed in https://www.jhipster.tech/production/ section Building an executable JAR / WAR file
I do not care about zuul, and only referenced the stackoverflow page above to give an example of trying to pass through port 8080 to 443 on a system level. The example was using iptables, but this did not work.
On the page https://www.jhipster.tech/production/#security, generation of a certificate was given by using keytool,
me#mycomp:~mywebsitename$ sudo apt install keytool
[sudo] password for me:
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package keytool
This is on an up to date kubuntu 20.04 system.
On the page https://www.jhipster.tech/production/#security it is mentioned that there is tutorial to use Let's Encrypt, https://maximilian-boehm.com/hp2121/Create-a-Java-Keystore-JKS-from-Let-s-Encrypt-Certificates.htm, this returns a 404.
Further down the page, it is suggested that it is possible to use the Apache HTTP server,
me#comp:~/mywebsitename$ sudo apt-get install -y apache2 python-certbot-apache
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package python-certbot-apache is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
python3-certbot-apache
E: Package 'python-certbot-apache' has no installation candidate
I'll add more details later. Anyone know of any working guides out there?