The database process was killed by the OS due to excessive memory consumpti

Hi,

The above error message makes it clear that the instance is crashing due to "Out of memory" (OOM) error on the Aurora instance.

To troubleshoot, I would recommend you to:

1. Check the CloudWatch graph for "FreeableMemory" to understand the memory usage.

2. Use monitoring tools like Enhanced monitoring which provides a process list (RDS, OS and MySQL processes) with details about CPU, memory etc consumed by each process (Note: EM is at an additional cost).

3. I understand you are using default parameter group but sometimes the available memory may not be enough to handle the workload, in this case you would need to scale up your instance class (with more memory resource). You may choose from:
   [+]https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/Concepts.DBInstanceClass.html#Concepts.DBInstanceClass.Summary

4. You can consider enabling "slow_query_log" with appropriate "long_query_time". Then dig into the slow query logs for the exact time (before the restart) and review them with your DBA to see if there were any long running transaction active at the time of the issue. (Note: Logs take up space on the instance)

5. Make use of Performance insights (if supported for the version/instance class) to identify the CPU bottle neck and troubleshoot performance issues.

6. Please upgrade your cluster if running an old version of Aurora (as it could be a bug as well). You can refer the below link to see what improvements have been made in later versions:
   [+]For Aurora 5.6: https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/AuroraMySQL.Updates.11Updates.html
   [+]For Aurora 5.7: https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/AuroraMySQL.Updates.20Updates.html

I recommend you to upgrade your Aurora cluster to the latest version available which has all the bug fixes, major improvements.
[+]https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/AuroraMySQL.Updates.html