Aurora mysql: Started cross AZ failover to DB instance event

Question

I have a Aurora db cluster with 2 instance, a writer and a reader.  
Since I migrated from version 1.23 (mysql 5.6) to 2.10.1 (mysql 5.7) 
I had some failover. 
Could you help me to understand what can cause this behavoral?
What event can trigger a automatic failover?

Answer

Hi, Good Question.

If the only thing that has changed is the version (2.10.1/MySQL 5.7 from 1.23/MySQL 5.6), check out:
https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/AuroraMySQL.Updates.2101.html.

Upgrading to 2.10.1 from 1.23 is considered a *major* version upgrade for Aurora and has some changes that could cause different behavior:
*https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/AuroraMySQL.Updates.MajorVersionUpgrade.html#AuroraMySQL.Updates.MajorVersionUpgrade.1to2

See the following for information about 2.10.1:
* https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/AuroraMySQL.Updates.2101.html

From a 5.6 -> 5.7 MySQL perspective, there also are some changes:
* https://dev.mysql.com/doc/refman/5.7/en/mysql-nutshell.html

Aurora mysql: Started cross AZ failover to DB instance event

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