Yes, DNS can be cached at any point in the lookup chain. The TTL is supposed to be honored, but as discussed above this doesn’t always happen.

Would this reply be cached by the client’s ISP? So, next time 1.2.3.4 would be returned for MyDomainELB-918273645.us-east-1.elb.amazonaws.com from DNS cache without asking amazon?

Many thanks Shlomo for your reply.

All the best,
Ram

I’m glad you find this post helpful.

It sure would be great to use ELB as an internal component without incurring the extra bandwidth charge. Unfortunately that is not an option today. ELB is designed to be accessed via public IP addresses (which incur the internet bandwidth charge) because (presumably) the ELB system needs the ability to remap those public IP addresses to different virtual LB machines when one of them fails – exactly the same way you would remap an Elastic IP to recover from instance failure.

I guess it might be technically possible for AWS to deliver an ELB that is accessed via private IP addresses, for “internal-to-EC2″ use, but it would not be as resilient in the face of failure as “regular” ELB.

Awesome post!!

i’m using ec2 only for few month now and it keep on amaze me on how simple things are when using it correctly, i just implemented the ELB in our ec2 servers and it works perfectly, thank you for your great post!!!

one question though, from what i understand until now you can approach the load balancer only from the “outside” and i also would like to use the ELB to distribute internal requests between my instances within the cloud.. is it possible to create an EC2 load balancer which will work without going first outside the cloud?
i know it will work this way also but it will cost more and will take more time than if i could do it all internally.

once again, thank you for a great post!

Best,
Ram

If I understand correctly, you’re asking: “Is there a way to change the IP address of an instance from the AWS Management Console? And can you change the IP address of an instance whenever you want, for example once a day?”

Please correct me if I misunderstood your question.

Using the AWS Management Console (or the API, or the command-line tools) you can change the public IP address of an instance by associating and removing an Elastic IP. When you associate an Elastic IP, the original public IP address is released. When you remove an Elastic IP, a new public IP address is provided. Usually this new address is different from the original address (the address the instance had before the Elastic IP was associated), but sometimes it is the same.

To do this on a regular schedule you could write a script to call the appropriate command-line tools or API methods, and use standard scheduling tools (e.g. cron).

It’s likely that the tests are not causing the ELB to scale. This might be due to the DNS lookups on the JMeter hosts being improperly cached. Try launching the JMeter processes with the -D option to adjust the sun.net.inetaddr.ttl property as discussed in the article above.

I have not yet seen a ceiling for LB throughput in all the tests I’ve run and reviewed.

It looks to me that we are hitting the max throughput at ELB as we do not see any contention from the back end servers…

We are gardually increasing the request/seconds in 10 minutes duration.
Any Idea how to check what is the max throughput we can achieve from ELB?

Thanks a ton.