SEO impact on using headless CMS for assets and images

Question

So I have a Gatsby site with the content managed by Contentful. When I upload images and documents to Contentful, I'm supposed to retrieve those from images.ctfassets.net and assets.ctfassets.net respectively.

Previously, when all those assets are self-hosted, I can see Google is able to discover and index those. I would like to know will Google be able to discover and index those assets if I store them in CMS instead?

Edit

Another question, by default Contentful returns the URL of the assets as //images.ctfassets.net/... instead of https://images.ctfassets.net/..... Although I have no issue with linking and displaying these assets on my website, will it affect SEO?

Answer 1

Yes these assets will be discovered and indexed, as long as the CDN does not explicitly do things to discourage or prevent indexing (such as by blocking crawling with robots.txt or blocking indexing with a robots noindex header.)

Google indexes images according to the page they appear on, so your images should still be considered a part of your site in the index, and theoretically there should be no change to your image ranking or indexation status (consider creating proper redirects to the CDN, though).

PDF documents, on the other hand, are treated as their own standalone web pages for purposes of indexation. So they will be indexed on the ctfassets.net domain, and are likely to inherit ranking signals from that domain rather than from your own domain. If you do not have the specific goal of trying to rank these PDF documents highly in the search results pages for competitive keywords, then it's nothing to worry about.

To answer your follow-up, linking by using the protocol-relative // url scheme will not affect your SEO in any negative way. It just means that your assets will be loaded as http when embedded/linked from http pages, and as https when embedded/linked from https pages. There are some non-seo-related reasons to always use https and avoid protocol-relative URLs, though it isn't a big deal in the big picture.