Tell me more ×
Server Fault is a question and answer site for professional system and network administrators. It's 100% free, no registration required.
up vote 2 down vote favorite

I have several server. We want set up new big service (word 'big' came from my boss :P ). I want use two Cisco LoadBalancer ACE 4700 but what will it happen if one of ACE is down? So I want setup DNS loadbalancing between this two device.

My goal is protect against failure of one Load Balancer using DNS.

Can you say - how to do? Use Round robin is good idea? or bad? Help me please.

Sorry for my english. Thanks for answer

share|improve this question

2 Answers

up vote 1 down vote accepted

We do DNS load balancing(sharing would be the right word) and DNS failover using dnsmadeeasy.com service. So we have multiple records for same DNS names and in DNS made easy you can configure failover and monitoring and is is not expensive either. We have had this save us multiple times.

Here is the catch: If you are using session persistence in your user sessions, don't use DNS load balancing. Only use DNS failover and that works great too.

And to answer Ladadadada's concern, you can set ttl very low. We use 60 seconds for the ttl.

share|improve this answer
Setting the TTL as low as 60 seconds should work well for a high percentage of your users. Some DNS servers ignore your TTLs and use their own, usually at around the 24 hour mark. There will also be some added latency in all requests every 60 seconds as users will need to go back to the authoritative nameservers again. As long as you can live with this, low TTLs are an adequate solution. – Ladadadada May 24 '12 at 9:22
up vote 1 down vote

DNS round robin load balancing is good for spreading load but it is not good for failover or redundancy. The reason for this is that DNS records are cached, usually for many hours. If one of your load balancers goes down, 50% of your users will already have that IP address as the result for your domain and will keep using it until their cache expires.

I know that the Cisco CSS load balancers can be configured to act as a redundant pair so that each of them monitors the health of the other. Only one of them handles traffic at any given time but if that one goes down, the other one takes over immediately. You only need one IP address for this kind of setup.

I don't know about the ACE product line but I would be surprised if they couldn't do the same sort of thing. A quick Google suggests that it does support some kind of failover.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.