Why No shard becomes primary on second node when it is UP again?

I have configured two node cluster and created an index with 4 shards and 1 replica
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Elastic created 2 primary shards on each node, this is how it looks from head plugin. shard 1, shard 3 are primary on node 1(stephen1c7) AND shard 0 and shard 2 are primary on node 2(stephen2c7)

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Shutdown one Node

Now i have shutdown the node 2(stephen2c7) to see if all the shards on node 1(stephen1c7) became primary. Yes, all shards are now primary.

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UP the shutdown node

Now i have made the Node 2(stephen2c7) up again to see if any shards on this node will be primary. But surprisingly no shard on this node became primary. Waited for long time but still no shard is primary on Node 2.
Why so?

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Is there any configuration to set for making the shards primary again after a node is up?

Thanks in advance!

It's not really important where primaries and secondaries are allocated.

All will get the same load basically

@dadoonet is that true for write operations also? why can't elastic make any shard on node2 as primary?

is that true for write operations also?

Yes. Write operations will happen on both shards (primary and replica).

why can't elastic make any shard on node2 as primary?

Why would it do that if the load is the same?

Got it ! Thank you @dadoonet. Are write operations happening in synchronous or asynchronous?
(Writing to primary and then secondary OR start writing to primary and secondary at same time)

Writing to primary and then all secondaries in parallel

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