Assume you are running Apache? If so lots of instructions out there for enabling SSL there.
For observium, I have a redirect rule for anything on tcp/80 as follows that does the redirect for me in the apache conf file (see the bottom virtual host to see the redirect rule). I'm sure there's 20 other ways to do it but this is working for me
NameVirtualHost *:443
<IfModule mod_ssl.c>
<VirtualHost *:443>
DocumentRoot /opt/observium/html/
CustomLog /opt/observium/logs/access_log combined
ErrorLog /opt/observium/logs/error_log
<Directory "/opt/observium/html/">
AllowOverride All
Options FollowSymLinks MultiViews
</Directory>
SSLEngine on
SSLCertificateFile /etc/ssl/localcerts/apache.pem
SSLCertificateKeyFile /etc/ssl/localcerts/apache.key
<FilesMatch "\.(cgi|shtml|phtml|php)$">
SSLOptions +StdEnvVars
</FilesMatch>
<Directory /usr/lib/cgi-bin>
SSLOptions +StdEnvVars
</Directory>
BrowserMatch "MSIE [2-6]" \
nokeepalive ssl-unclean-shutdown \
downgrade-1.0 force-response-1.0
BrowserMatch "MSIE [17-9]" ssl-unclean-shutdown
Alias /provision /var/www/provision
<Directory /var/www/provision>
Order allow,deny
Allow from all
</directory>
Alias /phpmyadmin /var/www/phpmyadmin
<Directory /var/www/phpmyadmin>
Order allow,deny
Allow from all
</Directory>
</VirtualHost>