Fallback to default DB to fallback db if shard is down

[rahul-mishra1]

We encountered one issue, one of our shard is down due to heavy load due to which all instances gets down as every instance has same database.yml is it possible that we add one fallback DB if any shard is down when we sent the fallback db for that so that it will impact user of only that shard and things will work for other shard also we Add some configuration to send notification in case of fallback mechanism

Any help will be appreciated