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Auto-scaling is not working with Neptune cluster except when primary writer instance type db.r5d.xlarge.

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Issue: Scale-up actions work fine with any instance size, the scale-in action is triggered by the CloudWatch but is not able to remove the readers except r5d.xlarge.

I am trying to Auto-scale the Amazon Neptune database to meet workload demands, But I'm getting issues while the Neptune writer is r5d.xlarge then it's working fine but when I changed the writer instance size then it's not working.

I did not set neptune_autoscaling_config on the cluster parameter group. Applied the same configuration which is in the reference blog post, but the one thing is different when I created the auto-scaling the first time was that time Writer instance was on r5d.xlarge. after that, I changed the writer instance size to t3.medium and then I deleted the old configuration of the auto-scaling app and scaling policy, deregistered the scale targets, and then created new everything about autoscaling, then after the scale-up action is working fine, but the scale-in action is not working except r5d.xlarge.

I am not getting any error from the CloudWatch, CloudWatch action triggered successfully but it does not remove the Neptune reader which was created while the scale-up action, and also I'm not getting scaling activities which policy action is not able to delete the reader.

This same thing is working fine on our Prod and Stage accounts but this issue has only occurred on the Dev account.

Note: Scale-in(remove neptune reader) is working fine through a scheduled action https://docs.aws.amazon.com/autoscaling/application/userguide/examples-scheduled-actions.html

Can anyone please help me with this?

Thanks in advance!

Below blog which I am using for reference https://aws.amazon.com/blogs/database/auto-scale-your-amazon-neptune-database-to-meet-workload-demands/

  • When you say "scale-up", do you mean "scale-out"? Neptune auto-scaling only supports scaling-out and scaling-in read replicas. The writer instance is not affected during these operations. You also must have at least one read-replica already provisioned before enabling auto-scaling. Auto-scaling can then scale-in the number of replicas to 0, but it needs this first replica online to start with.

  • Hello Taylor-AWS, Thanks for your response. Yes, when I say scale-up means scale-out. Here I am talking about Neptune read replicas scale-out and scale-in process. I didn't set up anything to an auto-scaling application in which a fixed instance type reader will be added, It's default setting will take instance size as the same writer instance size so, I mentioned about writer here. when my writer instance is r5d.xlarge then the auto-scale application trigger action for scale-out and scale-in it's working fine but when my writer instance is running on except r5d.xlarge then only scale-out is working fine but scale-in is not working. I already have one reader and writer instance with Neptune cluster at the time of configurations and I set min-capacity as 1 and max-capacity as 2. Also as I mentioned in my question it is working fine with our prod and stage accounts but the issue occurs in the Dev environment.

    Thanks!