Cloud Load Balancing, Part II

I wrote a post yesterday somewhat criticizing the statement by Radware. There was a very legitimate comment by the author asking about details, which I didn’t provide. This response is in a separate post, because it will get long. With a caveat that my knowledge of their product is minimal, here are the details:

• “key differences between a shared, cloud load balancer instance – offered by virtually all cloud providers (i.e. Amazon ELB, Rackspace CLB)” – that statement is misleading at best. AFAIK, Amazon didn’t disclose the architecture of their ELBs. It’s quite possible that they are shared, but that can’t be claimed for certain. In any case, it’s irrelevant. What matters is performance and features. ELB features are bare bones, whereas the performance is debatable and any argument in that regard should be test/data driven.

• “When a load balancer fails, a new one with an identical configuration takes over” – that really depends on the distinction between DR and high availability. Amazon doesn’t provide SLAs for their ELBs, but you could run a single ELB in multiple availability zones, multiple ELBs or ELBs in different regions. In these cases failover would typically be handled by DNS either by distributing multiple A records initially or updating DNS based on failure (albeit that depends on your RTO tolerance). There are other more obscure DNS methods as well. If you’re going with an HAProxy approach, then your failover method likely includes a monitoring daemon (for logs, service state, etc) and kicking off an API call that at a minimum includes DisassociateAddress and AssociateAddress.

• “a failure induced by any tenant can cause a broader failure impacting multiple tenants, (i.e Amazon ELB failure June-29th, 2012)” – In theory this might be true, but in practice its false. In almost any major cloud you’re in a shared environment. Typically another tenant can affect your workload, but if someone’s failure can impact another tenant, then it’s a security breach of gigantic proportions. More importantly: Amazon’s ELB failure on June 29th had nothing to do with shared tenants whatsoever. At least as far as ELB is concerned it’s a false statement. It was a bug in AWS and that can happen with anyone’s offering.

• “the need to redesign the application due to lack of advanced…functionality” – compared to ELB, that’s true (if you need these features). However, as with most AWS functions, they don’t claim more than what they do. If you use HAProxy, nginx or another load balancer you’ll get all of this functionality and more. If you’re willing to pay the price you could even run a Netscaler.

• “lack of control over the load balancer performance and capacity” – needs proof with tests/data. Again, with something like Haproxy you have full control, though your performance may be affected

• “inability to define custom health monitoring” – with ELB the functionality is limited, though you could hit an http page that executes a custom written and a more sophisticated health check. That does require more work. Again, I might sound like a broken record, but Haproxy and others will load balance whatever you want with very complex checks.

• “inability to load balance and optimize application delivery across multiple data centers” – this goes back to an old debate about GSLB and all the issues associated with it. However, that is largely true. Balancing across regions can get complicated, but in my experience it’s driven more by the application data model rather than load balancing itself.

• “The ADC’s enterprise features alleviate all the shortcomings of cloud based load balancer” – honestly, I am not even sure what to say here. FUD * Marketing-talk.