尝试连接到 RDS 时出现 AWS EC2 Interminent UnknownHostException

Question

I am runnung Java Play on an ec2. When I started up my Play on prod, everything works great. However, after running it about a day, I will start seeing UnknownHostException when connecting to RDS instance. This prevents any transaction between ec2 and rds. If I restart the app again, it works fine again.

I already checked the connection pool and I am pretty sure it works fine. Also, I already tested this with networkaddress.cache.ttl = 0 and networkaddress.cache.negative.ttl = 0. However, I am still getting the error.

Anyone has thoughts on this?

Answer 1

Just moving this to an answer from the comments. This was fixed by stopping the EC2 instance and then restarting it. After which, the error was not seen again.

It did not fix itself in my case. I ended stopping/starting my ec2 instance and this fixed it permanently. My guess is that it got assigned to another (better configured) ec2 instance when I starting it back up.

What happens when you do this .

• New internal IP address, though could randomly be the same. [VPC instances keep same internal IP addresses through stop/start.]

• New external IP address (though could randomly be the same).

• If an Elastic IP address was associated with the instance before it was stopped, then you'll need to re-associate it after the start. [VPC instances keep Elastic IP addresses associated through stop/start.]

• Any contents on the instance's former ephemeral storage were wiped and you are given fresh ephemeral storage (often mounted as /mnt).

• You can leave an instance stopped for as long as you like and not get charged for run time (though you do get charged at a much lower rate for the EBS volume storage). See the next point.

• A fresh billing hour is started for the instance when you start it again. Eg, if you start a new instance and then stop/start it 3 times within the first 60 minutes, you'll get charged for 4 hours instead of 1.

• There is a small chance that EC2 will not have available slots of the correct instance type to run your instance when you want to start it again. I've had this happen and temporarily switched to a different, available instance type to get it running again.