Implementing Secure Sockets Layer (SSL) across part or all of your website is a recommended security goal to use on the vast majority of Drupal websites. Creating an encrypted link for data protects your website and users' information and assets. Acquia Cloud customers can and should add SSL to their websites. There are several important factors to consider when implementing SSL:
- Varnish - If you are an Acquia Cloud user, you can use Varnish through SSL. This can impact your caching strategy, and as always, you should plan your caching strategy with care and implement reasonable levels of testing before submitting a website to heavy or above average traffic loads. Without Varnish through SSL, assets and pages viewed over HTTPS will not be served from Varnish, even if external caching is enabled and visitors are anonymous. Using the Varnish through SSL feature allows Acquia Cloud to serve all pages and assets, secured or not, over HTTPS, which reduces server load.
Adding SSL to Varnish has a minor impact to performance, but this impact is generally well within normal hardware tolerances.
One method of ensuring that embedded resources are served using the correct protocol is to use the Pathologic module. You can learn more about how to use Pathologic on its documentation page. When setting this up, Correct URLs with Pathologic should be the last filter. Set Processed URL format to whichever method is most appropriate for your website. If you are switching to a fully SSL website, then set this option to Full URL.
- Redirects - Ensure that you have proper 301 redirects from your HTTP pages to HTTPS. If a website was already in production on HTTP, Google and other search engines most likely have indexed your public-facing pages. If you start serving everything over HTTPS, Google will treat these pages as a completely separate website. This can lead to duplicate content penalties, which can be frustrating and difficult to dig out from.
To ensure that this doesn't happen, add RewriteRule directives in your
.htaccessfile that rewrite all requests with a 301 status code to the old HTTP website back to HTTPS with the full query string intact. The next time Google crawls the page, it will see the permanent redirect status and update your website to be indexed under HTTPS, rather than creating a duplicate. If you are an Acquia Cloud user, read Redirecting traffic between HTTP and HTTPS on Acquia Cloud to find out how to set this up.
- Resources in general - Combine as many resource requests as possible. Serving content over HTTPS requires a slightly increased amount of overhead to account for the SSL handshake and negotiation. This results in a minimal amount of additional time required for asset transmission, but when you are sending hundreds of assets, such as images and stylesheets, it can quickly add up to a measurable amount. To solve this, combine as many images into sprites as is reasonable and ensure that CSS/JS Aggregation is enabled in Drupal to serve as few stylesheets as possible.
For websites with many images and resources, sourcing them from off server (that is, S3) is an alternative approach to reduce issues with negotiation speeds. However, this requires another SSL certificate for the second asset domain, although a wildcard could work for both domains. An example is the scenario in which you use
www.example.comfor the main website and
images.example.comas a second domain for only the images.
With the preceding in mind, you should have no issues switching your websites over to be protected by SSL across the board, rather than only protecting a few pages using modules.