In this setup, you use only WordPress' administration and Gatsby as a front-end for your site. There shouldn't be any public traffic to your WordPress installation, only the editors should have access and whatever server or process is responsible for building your Gatsby site.
Do you need two domain names
You don't need multiple domain names, you can expose WordPress on, for example, subdomain (wp.example.com) or in subdirectory (example.com/wordpress). Or you can use whatever domain the hosting provides you with (e.g. example.wordpress.com).
Do you need […] double hosting in this case, one for the WP site and one for the Gatsby site?
It's not necessary to host Gatsby and WordPress separately, but it will be probably easier. For example, you can use a hosted WordPress solution like WP Engine, WordPress.com, or a shared PHP hosting like Bluehost, DreamHost, Hostgator… and deploy your Gatsby site using static hosting like Netlify, GitHub Pages, Cloudflare Pages, or Gatsby Cloud. You can also build Gatsby site using, for example, GitHub Actions, and upload generated files to the shared hosting.
Can you use the free hosted wordpress.com in this case?
You need to install GraphQL plugins to WordPress to be usable as a data source by Gatsby. This is possible only with the pro plan.
Either way, don't you just end up with a duplicate site and how do you redirect traffic to and index only your Gatsby site?
Make sure to prevent indexing of the WordPress installation by search engines (with robots.txt, for example). Additionally there are more plugins to help you setup the WordPress installation as a headless CMS, like WPGatsby and Headless Mode (which takes care of redirects to the production site).
Anyway, personally I don't recommend using WordPress as a headless CMS (some reasons I recently explained elsewhere), especially if you don't have much experience with this setup. There are many hosted headless CMSs with generous free tiers, so you don't need to care about additional hosting for the CMS.
In my experience, WordPress seems attractive to some clients because the CMS itself is free, but the costs of hosting, maintenance, and additional development work outweigh the cost of a hosted headless CMS eventually.
In this setup, you use only WordPress' administration and Gatsby as a front-end for your site. There shouldn't be any public traffic to your WordPress installation, only the editors should have access and whatever server or process is responsible for building your Gatsby site.
You don't need multiple domain names, you can expose WordPress on, for example, subdomain (
wp.example.com) or in subdirectory (example.com/wordpress). Or you can use whatever domain the hosting provides you with (e.g.example.wordpress.com).It's not necessary to host Gatsby and WordPress separately, but it will be probably easier. For example, you can use a hosted WordPress solution like WP Engine, WordPress.com, or a shared PHP hosting like Bluehost, DreamHost, Hostgator… and deploy your Gatsby site using static hosting like Netlify, GitHub Pages, Cloudflare Pages, or Gatsby Cloud. You can also build Gatsby site using, for example, GitHub Actions, and upload generated files to the shared hosting.
You need to install GraphQL plugins to WordPress to be usable as a data source by Gatsby. This is possible only with the pro plan.
Make sure to prevent indexing of the WordPress installation by search engines (with robots.txt, for example). Additionally there are more plugins to help you setup the WordPress installation as a headless CMS, like WPGatsby and Headless Mode (which takes care of redirects to the production site).
Anyway, personally I don't recommend using WordPress as a headless CMS (some reasons I recently explained elsewhere), especially if you don't have much experience with this setup. There are many hosted headless CMSs with generous free tiers, so you don't need to care about additional hosting for the CMS.
In my experience, WordPress seems attractive to some clients because the CMS itself is free, but the costs of hosting, maintenance, and additional development work outweigh the cost of a hosted headless CMS eventually.
thanks a lot for your reply!