nats.docs/developer/reconnect/random.md

Avoiding the Thundering Herd

When a server goes down, there is a possible anti-pattern called the Thundering Herd where all of the clients try to reconnect immediately creating a denial of service attack. In order to prevent this, most NATS client libraries randomize the servers they attempt to connect to. This setting has no effect if only a single server is used, but in the case of a cluster, randomization, or shuffling, will ensure that no one server bears the brunt of the client reconnect attempts.

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