what device lets you add servers on the fly w/o waiting for IP/dns propagation?

Question

Is it a firewall or router that sits in front of the front-end servers, which basically gives you the ability to add/remove servers and not have to wait for DNS to propagate since you have your own little network with internal IPs?

Does this also give you the potential flexibility of routing traffic to another ISP? e.g. Say you have 2 front end servers, 1 db. You have another, identical setup, at another ISP for failover. (you synch. data every x minutes).

If ISP#1 db server goes down, can you route traffic to ISP#2 that is operational?

Answer 1

Switching between two different ISPs would be handled via BGP which would need to be done via a router.

A router (as long as it supports load ballancing) would also allow you to do put multiple machines behind a single public IP. If you will have a lot of traffic you'll want load balancers between the routers and the web servers to handle the actual load balancing.

Answer 2

Sounds like you are talking about NAT (Network address translation, which most routers and firewalls can do), having a private address space (such as 192.168.1.1-254) on your local network which 'Translates' to a real internet IP when traffic goes through the 'Device' onto the internet (or from the internet back in to your Lan).

This way you can have TCP Port 80 (Http) sent to one internal server, and TCP port 443 for example (https) sent to another.

However, I am not sure how this really helps you, sounds like you have two sites and want redundancy from site failure. If this is the case being able to change the port 'Mappings' between your internet IP and your local network IP's is not going to help you, as you are still only dealing with that one site.

DNS is your only real option for Internet side redundancy accross two sites (on the scale you are talking anyway, larger setups can use BGP for IP failover but this would require co-operation from both ISP's). You could always reduce the 'TTL' (Time to live) for your DNS servers. This is the time that other DNS servers will cache your DNS information for.

For example, if this is set to five minutes, every DNS server globally that caches your DNS information would expire after five minutes and any reauest after that would end up back at your DNS servers (and pickup any changes you may have made, such as site 2's IP). This of course greatly increases the load on your DNS servers and also means your online precence is reduced to 5 minutes if your authorotive DNS servers were all to go down for your domain.

Maybe try adding two A records (for both locations) to your DNS entry, if one cannot be found some browsers/dns libraries will try the other locaion anyway.

Answer 3

From an enterprise standpoint, the best way to accomplish what you're talking about is to have a load balancer in front of several servers, in a datacenter with redundant WAN links.