If your website is available under more than one FQDN, standard SEO advice is to pick a canonical FQDN and redirect the others to it. You can see that in action on this website: johntobin.ie/blog/smarter_http_redirects will redirect you to https://www.johntobin.ie/blog/smarter_http_redirects/. The simplest way to do this in Apache is to configure a VirtualHost for johntobin.ie, and use a single RewriteRule:
RewriteRule ^(.*)$ https://www.johntobin.ie$1
This also works for redirecting all HTTP requests to HTTPS requests.
You can improve this approach in two easy ways. Firstly, heed the SEO advice and turn that temporary redirect (302) into a permanent redirect (301), which browsers and (more importantly) search engines’ crawlers are supposed to cache.
RewriteRule ^(.*)$ https://www.johntobin.ie$1 [L,R=301]
See https://en.wikipedia.org/wiki/HTTP_response_codes for a list of HTTP response codes.
The second change will reduce the load on your web server slightly, and more
importantly will also slightly speed up your readers’ browsing experience (and
should therefore have some SEO benefits). You may have noticed that when you
click on a URL like https://www.example.org/directory, your browser will
display https://www.example.org/directory/ (note the trailing / on the
second URL). When your browser makes a HTTP request for a directory, but the
request doesn’t end with a /, the web server will redirect your browser to the
same URL with a / appended. When you combine that with a redirection from
example.org to www.example.org, your web browser will have to make three
requests:
http://example.org/directory
http://www.example.org/directory
http://www.example.org/directory/
This is even worse if you subsequently redirect from http://www.example.org/ to https://www.example.org/ because that adds a fourth request.
We can reduce the sequence to two requests by appending a / whenever a request
is missing one and redirecting to HTTPS rather than HTTP.
Here’s the Apache config snippet:
# Add a trailing / if a request for a directory is missing one.
# This avoids an extra redirection: instead of
# http://johntobin.ie/blog -> https://www.johntobin.ie/blog ->
# https://www.johntobin.ie/blog/
# we get
# http://johntobin.ie/blog -> https://www.johntobin.ie/blog/
#
# If the request is for a directory . . .
RewriteCond %{DOCUMENT_ROOT}/%{REQUEST_URI} -d
# . . . and the URL doesn't end with a / . . .
RewriteCond %{REQUEST_URI} !/$
# append a /, and fall through to the next RewriteRule.
RewriteRule ^(.*)$ $1/
# Redirect as before.
RewriteRule ^(.*)$ https://www.johntobin.ie$1 [L,R=301]