If you read further in the article there appear to be 6 SQL Server machines (across 2 clusters). Those are some highly spec'd servers with huge amounts of RAM a

If you read further in the article there appear to be 6 SQL Server machines (across 2 clusters). Those are some highly spec'd servers with huge amounts of RAM and CPUs. With decent caching the SQL Server machines wouldn't be hit too often either, hence the Redis and Elasticsearch servers. Fewer, but larger DB servers would typically mean much less maintenance and dev ops headaches. As others have said, skipping best practices is typically reasoned out really well before proceeding. Not everyone needs every best practice.