Round Robin A Records

[Kevin Darcy]

Steve Ford wrote:

> Can someone please advise:
>
> We have two web servers mirrored. We have setup DNS (BIND 4.9.7) like
> this to round robin the requests:
>
> www    0300    IN A    198.141.222.111
>             0300    IN A    198.141.223.117
>
> When a client attempts to resolve the address of the hostname 'www' is
> it true that the client will receive one of the IP addresses on a round
> robin basis?
>
> If we lose one of the servers, say it is booted down, every second
> request will be the IP address of the unavailable server.

Modern clients will fail over to the second address, after a short delay.

> Does anyone know a way of configuring DNS so that if one server is down
> all requests are directed to the available server dynamically? Manually
> we remove the A record for the unavailable server.

If you want to spend a significant amount of money, you could buy one of
those "load balancer" devices.

Another thing to consider, if you're on a budget and the web servers
happen to be on the same segment, is just bringing up a virtual interface
on one web server when the other one is down. Poor man's clustering.

Of course, it's not very redundant for both servers to be the same segment
anyway; then the network itself becomes a single point of failure. But
this could work quite well with multiple clusters on different segments...


- Kevin