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If you're wondering how many master nodes I've seen in a single cluster, it would have to one of my clients who is running in the 100s of worker nodes. When we were designing the cluster layout they let me know I had 24 nodes designated to be master nodes (this is excluding any edge/ingestion nodes, too). I was blow blown away and I talked them back down to 15 which is PLENTY as you can see by the following layout.
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