With the focus on all sites to be secure (ie, via HTTPS), the conversion of existing sites to be SSL based connections is becoming virtually mandatory for all sites. If you've seen "Not Secure" listed in your URL bar for your site, this is an indication that you need to convert your site over.
There are a few tasks involved to convert your site over, which we have detailed below.
1. Install the SSL Certificate
This can be done in two different ways. The first is with a generated certificate (for example, an EV certificate) which needs to be uploaded to Plesk. To do this, you can follow our handy guide: https://www.conetix.com.au/support/article/plesk-onyx-install-ssl-certificate
The second way is to use the free service from Let's Encrypt: https://www.conetix.com.au/support/article/plesk-onyx-how-install-lets-encrypt-ssl As this automatically renews
2. Correct all hard-coded links
If these links aren't set to HTTPS, you may see a mixed-content error. We have an article on how to find these links: https://www.conetix.com.au/support/article/how-find-insecure-http-based-calls-mixed-content
3. Update Google Search Console
Unfortunately the Google Search Console (previously known as the Google Webmaster Tools) doesn't detect that you've changed from HTTP to HTTPS. As of October 2017 (when this article was written), there's no easy way to edit your existing settings. This is considered to be a "site move", which Google have a documented procedure for here: https://support.google.com/webmasters/answer/6033049
4. Google Analytics
While your tracking code won't change, but it can be beneficial to ensure the default property is set to HTTPS and after updating the Google Search Console that the site is correctly linked. You can find further assistance in the Google Analytics help area: https://support.google.com/analytics.
5. SEO Ranking
As theres potential Search Engine Optimisation (SEO) implications for the move, you should ensure that all links back to your HTTP based site automatically redirect (using a 301) to HTTPS. Within Plesk, this can be achieved by simply selecting a tick box: https://www.conetix.com.au/support/article/plesk-onyx-redirect-http-https.
Overall, there's measurable SEO boost by converting your site to HTTPS to take advantage of the latest speed improvements as well as Google ranking indicators. There's also the potential for a temporary dip in rankings, but based on what we've seen this doesn't affect all sites and those who have it's a 1-2 day dip.
Google Best Practices for HTTPS: https://support.google.com/webmasters/answer/6073543?hl=en
Moz.com SEO HTTPS Tips: https://moz.com/blog/seo-tips-https-ssl
KeyCDN Guide: https://www.keycdn.com/blog/http-to-https/