Amazon RDS 中是否可以有超过 5 个只读副本？

Question

The Amazon RDS FAQ seems to suggest that you can't have more than 5 replicas. Is there any workaround?

Answer 1

No. Amazon only allows you to create up to 5 replicas, and need to be launched one by one.

If You need more than 5 you can create a Master-slave configuration using EC instances, then you can have as many replicas as you want.

Answer 2

Currently there is a workaround that allows to have more than 5 read replicas - by creating read replicas of existing read replicas. It's still up to 5 read replicas per DB, and up to 2 layers (so max 30 read replicas in total).

To enable read replica to have read replicas, automated backups must be turned on:

http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_ReadRepl.html#USER_ReadRepl.MySQL

Answer 3

Five read replica's are more than enough for most of the times. More than 5 can impact the performance.

Scale up technique: if you are using m1.xlarge, you can scale up to Quadrapule EXL and get better performance with 5 RR itslef.

If your system demands more than 5 you can solve this by refining your architecture in following ways:

P1) Functionally partition the DB and have read replica's accordingly

P2) Offload read traffic to Amazon ElastiCache and DynamoDB

Answer 4

One flavor of RDS Engine type - Aurora (for MySQL / PostgreSQL) supports up to 15 read replicas https://docs.amazonaws.cn/en_us/AmazonRDS/latest/AuroraUserGuide/Aurora.Replication.html

Answer 5

10 years later, RDS limits can be lifted. Look for "Yes" in the "Adjustable" column:

• https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_Limits.html#RDS_Limits.Limits

The usual caveats apply for measuring performance impact of additional replicas on the primary.