Are you using VPC or EC2-Classic networking? The M3 supports EC2-Classic whereas the T3 family does not, and confusingly you get the ICE message because that is what EC2 returns to RDS when it asks EC2 to give it a EC2-Classic T3 instance.
I understand that you are receiving the below error while modifying your RDS instance from db.m3.medium instance to a db.t3.medium
Cannot modify the instance class because there are no instances of the requested class available in the current instance's availability zone. Please try your request again at a later time. (Service: AmazonRDS; Status Code: 400; Error Code: InsufficientDBInstanceCapacity; Request ID: 6696291a-8cd2-4005-aafc-ae42570e65cd)
I would like to inform you that, the above error can occur in two scenarios:
Scenario 1: If your current oracle DB instance (m3.medium) is residing in an EC2 classic network
-- As you might be aware of, that there are two types of platform supported by RDS instances namely "EC2-VPC and EC2-Classic Platform". The below link will check the environment of your DB instance:
[+] Determining Whether You Are Using the EC2-VPC or EC2-Classic Platform - https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_VPC.FindDefaultVPC.html
-- In "EC2-Classic Platform", there are only some specific RDS instance class types that are available for this platform.
1. db.m3 – Previous Generation Standard Instance Classes
2. db.m1 – Previous Generation Standard Instance Classes
3. db.r3 – Previous Generation Memory Optimized Instance Classes
4. db.m2 – Previous Generation Memory Optimized Instance Classes
\[+] Instance Types Available in EC2-Classic - https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-classic-platform.html#ec2-classic-instance-types
-- Further, the DB instance types belonging to the M5, M4, R4 , T3 and T2 family (current generation instances) can only be launched in a VPC. They cannot be launched in an EC2 classic network(Not in VPC).
-- Also, we cannot modify the instance types of existing RDS instances which are not in VPC to either M5 or M4 or T2 or T3 or R4 as these instance types are not supported by the Classic Network. They can be only launched in a VPC. This is the reason why you were receiving an error.
-- To be able to modify your DB instance from m3 to t3, you have to move your RDS instance from EC2 Classic to VPC platform. The below links will help you with the same:
[+] Moving a DB Instance Not in a VPC into a VPC - https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_VPC.html#USER_VPC.Non-VPC2VPC
\[+] Ec2 Classic to VPC with minimal downtime - https://d0.awsstatic.com/whitepapers/RDS/Moving_RDS_MySQL_DB_to_VPC.pdf
Scenario 2: The DB instance type db.t3.medium is currently not available in the availability zone eu-west-1
-- Alternatively, the error can occur times during times where there is high demand for RDS instance types in a given region.
-- In other words, the above error arises when the DB instance type db.t3.medium is not available in the availability zone in which the DB instance is residing (i.e. eu-west-1).
AWS does try to avoid this and have sufficient capacity for our customers but as this relates to the availability of physical hardware and the instances it takes time for us to physically increase the overall general capacity to meet new trends in customer demand. Unfortunately, we are not able to provide any kind of ETA when the instances will be available in your desired region.
-- In this case, you can consider one of the below options:
1. Try to upscale without specifying an Availability Zone.
2. Try up-scaling to a different instance type (which you can resize at a later stage).
I hope this helps.
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