Merge branch 'docs-ref-arch-non-official-methods' into 'master'

Add section on supported deviations from the ref architectures

See merge request gitlab-org/gitlab!47276

doc/administration/reference_architectures/index.md

@@ -151,7 +151,27 @@ is recommended.
 instance to other geographical locations as a read-only fully operational instance
 that can also be promoted in case of disaster.
 
-## Configuring select components with Cloud Native Helm
+## Deviating from the suggested reference architectures
+
+As a general rule of thumb, the further away you move from the Reference Architectures,
+the harder it will be get support for it. With any deviation, you're introducing
+a layer of complexity that will add challenges to finding out where potential
+issues might lie.
+
+The reference architectures use the official GitLab Linux packages (Omnibus
+GitLab) to install and configure the various components (with one notable exception being the suggested select Cloud Native installation method described below). The components are
+installed on separate machines (virtualized or bare metal), with machine hardware
+requirements listed in the "Configuration" column and equivalent VM standard sizes listed
+in GCP/AWS/Azure columns of each [available reference architecture](#available-reference-architectures).
+
+Running components on Docker (including Compose) with the same specs should be fine, as Docker is well known in terms of support.
+However, it is still an additional layer and may still add some support complexities, such as not being able to run `strace` easily in containers.
+
+Other technologies, like [Docker swarm](https://docs.docker.com/engine/swarm/)
+are not officially supported, but can be implemented at your own risk. In that
+case, GitLab Support will not be able to help you.
+
+### Configuring select components with Cloud Native Helm
 
 We also provide [Helm charts](https://docs.gitlab.com/charts/) as a Cloud Native installation
 method for GitLab. For the reference architectures, select components can be set up in this