Randomize brokers to connect to from the connection seed

[fjuan]

In order to better spread connection load towards brokers, clients could randomize the one broker selected to initiate the connection from the seed brokers list.

kafkajs/src/cluster/connectionBuilder.js

Line 33 in 0b70749

const [seedHost, seedPort] = brokers[index++ % size].split(':')

The randomization mechanism should be aware of the possiblity that the selected broker is not available. A suggestion could be to change the default index value at

kafkajs/src/cluster/connectionBuilder.js

Lines 26 to 27 in 0b70749

	const size = brokers.length
	let index = 0

Maybe something like

let index = Math.floor(Math.random() * size)

[fjuan]

Another implementation idea would be to shuffle the list of brokers right after reading it and keep the current connectionBuilder.js as is. Suggestion from @matthiasfeist

[Nevon]

I'm of two minds on this.

On the one hand, this is probably the behavior you want in 90% of cases, so from that perspective it makes sense for us to handle it internally.

On the other hand, there may be situations where you actually want to prefer connecting to a certain broker, which would become impossible to do if we force a random order. If we don't do this in the client, it's still easily implementable in userland code by just shuffling the list before handing it to the client.

Of course there's always the option of shuffling the list by default and then introducing a way to disable that later if/when it becomes needed.

[tulios]

Out on pre-release 1.12.0-beta.21