There seems to be no standard. Looking back at the various diagrams that people used to represent the distributed cache, Cameron Purdy plots still seem like the best explanatory plots. Cameron launched Tangosol, which was later acquired by Oracle. I would go with a miniature cloud hiding or containing four database servers. Arrows may also be interconnected. You just want to make sure that it is not too similar to a “cloud” like Azure. You don’t want it to look like you are going through the Internet to get there, but rather that there are “4” database servers that “work together”. You can also just use database cylinders located one above the other.