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The second article is too old, so, I think we should refer to the first article. But as far as I am concerned, both UDP and TCP randomly allocated high ports can be used for cluster service. It all depends on your requirement.
TCP is more reliable since it guarantees the delivery of data to the destination and manages retransmissions in case of lost parts. However, UDP is faster, simpler, and more efficient than TCP as it avoids the unnecessary overheads of TCP transport. UDP is incredibly efficient in terms of bandwidth, and much less demanding of poor performing networks, as well.
Hope above information can help you.
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