How to prevent performance degradation while recovery

ElasticSearch is very awesome, but I really really want ElasticSearch to be
more robust with recovery situation.

Today, 2 elasticsearch instances were down. (don't worry, servers were
rebooted by AWS) and cluster status was gone to yellow.

The problem was, a lot of bulk index requests were dropped due to timeout
with 10s.

Is there anybody who knows how to mitigate this problem such as parameter
values?

Would it be better if I change c.r.a parameters? If so, what would be
tuning values?

Thank you
Best, Jae

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