Lambda to RDS database connection takes 6 seconds.
I have a Lambda function and a Postgres Serverless V2 RDS instance in us-west-2. The Lambda function frequently takes 6 seconds to establish a database connection to the RDS instance with IAM Authentication, and I have profiled the code to confirm that the time is spent on the actual connection process, not on cold starts, or creating the IAM Authentication token. Below you can see a sample from X-Ray:
You can see that the connection function is taking 6 seconds. There is also a subsegment which is getting the IAM Auth token in 150ms. The rest of the time is spent connecting. This is a relatively new trend (last couple of days), because it just started tripping my Cloudwatch Alarms.
My backend code is Python 3.11, using psycopg2. After the IAM Auth token is negotiated, I immediately call psycopg2.connect and the function completes. So there is nothing else taking time, and I am fairly confident that there is something wrong with the network or the database.
How can I debug this? How can I improve this connection time?
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I had 2 pending database maintenance actions. One for a postgres minor version upgrade, and another for an OS patch. I applied both of those upgrades and the connectivity latency has dropped back down to sub-second. This suggests that the db or the OS had accumulated some connection cruft that was slowing down its ability to provision new connections. I hope this helps someone else.
