AWS Aurora Serverless - Communication Link Failure

Question

I'm using MySQL Aurora Serverless cluster (with the Data API enabled) in my python code and I am getting a communications link failure exception. This usually occurs when the cluster has been dormant for some time.

But, once the cluster is active, I get no error. I have to send 3-4 requests every time before it works fine.

Exception detail:

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server. An error occurred (BadRequestException) when calling the ExecuteStatement operation: Communications link failure

How can I solve this issue? I am using standard boto3 library

Answer 1

Here is the reply from AWS Premium Business Support.

Summary: It is an expected behavior

Detailed Answer:

I can see that you receive this error when your Aurora Serverless instance is inactive and you stop receiving it once your instance is active and accepting connection. Please note that this is an expected behavior. In general, Aurora Serverless works differently than Provisioned Aurora , In Aurora Serverless, while the cluster is "dormant" it has no compute resources assigned to it and when a db. connection is received, Compute resources are assigned. Because of this behavior, you will have to "wake up" the clusters and it may take a few minutes for the first connection to succeed as you have seen.

In order to avoid that you may consider increasing the timeout on the client side. Also, if you have enabled Pause, you may consider disabling it [2]. After disabling Pause, you can also adjust the minimum Aurora capacity unit to higher value to make sure that your Cluster always having enough computing resource to serve the new connections [3]. Please note that adjusting the minimum ACU might increase the cost of service [4].

Also note that Aurora Serverless is only recommend for certain workloads [5]. If your workload is highly predictable and your application needs to access the DB on a regular basis, I would recommend you use Provisioned Aurora cluster/instance to insure high availability of your business.

[2] How Aurora Serverless Works - Automatic Pause and Resume for Aurora Serverless - https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/aurora-serverless.how-it-works.html#aurora-serverless.how-it-works.pause-resume

[3] Setting the Capacity of an Aurora Serverless DB Cluster - https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/aurora-serverless.setting-capacity.html

[4] Aurora Serverless Price https://aws.amazon.com/rds/aurora/serverless/

[5] Using Amazon Aurora Serverless - Use Cases for Aurora Serverless - https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/aurora-serverless.html#aurora-serverless.use-cases