Problem description
When using gh-ost for lock-free DDL changes in RDS MySQL, you might encounter an error similar to: Scan error on column index 0, name "@@global.port": converting NULL to int is unsupported.
Cause
This issue occurs because certain parameters are not configured when executing the gh-ost command.
Solution
When using gh-ost for lock-free DDL changes in RDS MySQL, you need to include the following parameters:
--allow-on-master
--assume-rbr
--assume-master-host
--aliyun-rds