Finally I want to activate SSL with GL 1.8.2 or so. Is there anything I have to consider? Do I have to use migrate.php to change the URL?

Besides changing all the URLs in the Configuration to use https you need to change the Cookie to Secure.

You should also run Migration as it will do the above (I believe but not sure due to the old version) along with changing any hard coded URL for internal links and images to the new URL for plugins that support it.

You should also check your theme files incase they link directly to images and change those as well. They shouldn't but you never know. This also includes the header.thtml file incase it links directly to any other resources like css and js files.

These should be easy to spot as when a page is loaded using https if anything is loaded from your website using only http the browser will display and error stating the website is not secure.

On a related note I would also updated your .htaccess file and create a URL rewrite rule to convert all incoming http requests to https. This will help the search engines greatly and keep any backlinks you have from other websites intact. (very important in terms of keeping your rankings in the search engines). There are tools available on the internet that help you test rewrite rules to ensure they are setup properly.

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One of the Geeklog Core Developers.

Usually, a dedicated IP address is required for SSL installation. However, if you have SNI technology available on your server, you can install your SSL certificate on a shared IP address. Check SNI availability for your hostname with your hosting provider prior to SSL certificate activation in order to avoid any of the known issues that may occur with this type of SSL certificate installation. Ensure to locate and back up the RSA private key that will arrive with your CSR code, as it will be required for the installation. It will not be possible to install the certificate without this code. Ask your hosting company to advise you on the server type (software your server is using for CSR generation) for your hostname. This will be useful information to have during installation. Note: Please make sure that your hosting provider supports third-party SSL certificates!