# pt-online-schema-change for RDS instance with Read Replica behind VPC

**URL:** <https://forums.percona.com/t/pt-online-schema-change-for-rds-instance-with-read-replica-behind-vpc/4362>\
**Category:** Percona Toolkit\
**Created:** [August 20, 2015, 7:24am UTC](https://forums.percona.com/t/pt-online-schema-change-for-rds-instance-with-read-replica-behind-vpc/4362 "2015-08-20T07:24:07Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Shakkalakka](https://avatars.discourse-cdn.com/v4/letter/s/ccd318/32.png) [@Shakkalakka](https://forums.percona.com/u/Shakkalakka)\
**Post date:** [August 20, 2015, 7:24am UTC](https://forums.percona.com/t/pt-online-schema-change-for-rds-instance-with-read-replica-behind-vpc/4362/1 "2015-08-20T07:24:07Z")

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Hi,

I require running pt-online-schema-change for a MySQL 5.6 DB instance under AWS RDS.  
The same instance is behind a VPC, and it has a Read Replica. AWS manages its VPC read replicas under a different subnet than the original instance.

How would you go about executing this tool in this case?  
When I tried doing it using --recursion-method  
No slaves found. See --recursion-method if host has slaves.  
Not checking slave lag because no slaves were found and --check-slave-lag was not specified.  
Can’t use an undefined value as an ARRAY reference at /usr/bin/pt-online-schema-change line 7135, line 1.

Is it possible that the replication under the VPC works with a different IP than the “public IP” of the Replica, and that’s why Percona is unable to discover the replica?

Thanks for your assistance,  
Eran