Cancel/Undo A Pending Modifcation On AWS RDS - 2020-01-06

Canceling a pending modification isn’t described all that well in the AWS documentation, so gave it a try and wrote it down.

I tested it multiple times with RDS/Aurora instances and it works as expected, even without the --apply-immediately parameter (at least for the instance class modifications).

Full Example

Let’s change the instance class for an Aurora instance called database-2-instance-1 from db.t3.medium to db.r4.large and undo it again afterwards. None of these commands do impact the availability of the database.

Note: Using jq here to only output the important parts.

Check instance class

aws rds describe-db-instances --db-instance-identifier database-2-instance-1 | jq '.DBInstances[].DBInstanceClass'
"db.t3.medium"

Validate that there is no pending modification

aws rds describe-db-instances --db-instance-identifier database-2-instance-1 | jq '.DBInstances[].PendingModifiedValues'
{}

Modify instance class

This modification will result in a change of the instance class in the next maintenance window.

aws rds modify-db-instance --db-instance-identifier database-2-instance-1 --db-instance-class db.r4.large | jq '.DBInstance.PendingModifiedValues'
{
  "DBInstanceClass": "db.r4.large"
}

Validate again

Just to be sure, check if everything looks as expected.

aws rds describe-db-instances --db-instance-identifier database-2-instance-1 | jq '.DBInstances[].PendingModifiedValues'
{
  "DBInstanceClass": "db.r4.large"
}

Undo modify of instance class

This is the important part which modifies the instance class back to the old value. The documentation describes that a --apply-immediately is required, but it turns out that that is not the case. At least in this example.

aws rds modify-db-instance --db-instance-identifier database-2-instance-1 --db-instance-class db.t3.medium | jq '.DBInstance.PendingModifiedValues'
{}

Validate the removed pending modification

aws rds describe-db-instances --db-instance-identifier database-2-instance-1 | jq '.DBInstances[].PendingModifiedValues'
{}

At this point the pending modification is gone.