How do most browsers behave if they get multiple A-records from the DNS server? Do the stick to one IP as long as it is reachable (and only use another if the IP is down)? Or do they switch all the time for no reason?
If the majority current browsers stick to one IP, DNS-RR would be enough for me as a simple failover solution.
We received an interesting "requirement" from a client today.
They want 100% uptime with off-site failover on a web application. From our web application's viewpoint, this isn't an issue. It was designed to be able to scale out across multiple database servers, etc.
However, from a networking issue I just can't seem to figure out how to make it work.
In a nutshell, the application will live on servers within the client's network. It is accessed by both internal and external people. They want us to maintain an off-site copy of the system that in the event of a serious failure at their premises would immediately pick up and take over.
Now we know there is absolutely no way to resolve it for internal people (carrier pigeon?), but they want the external users to not even notice.
Quite frankly, I haven't the foggiest idea of how this might be possible. It seems that if they lose Internet connectivity then we would have to do a DNS change to forward traffic to the external machines... Which, of course, takes time.
Ideas?
UPDATE
I had a discussion with the client today and they clarified on the issue.
They stuck by the 100% number, saying the application should stay active even in the event of a flood. However, that requirement only kicks in if we host it for them. They said they would handle the uptime requirement if the application lives entirely on their servers. You can guess my response.
I am looking for a solution to load balancing and failover strategy, mainly for big web applications. We have many services to be balanced, such as web, MySQL, and many other HTTP or TCP based services. But I am not sure what their pros and cons are, and which I should choose.
I'm using nginx and NginxHttpUpstreamModule for loadbalancing. My config is very simple:
upstream lb {
server 127.0.0.1:8081;
server 127.0.0.1:8082;
}
server {
listen 89;
server_name localhost;
location / {
proxy_pass http://lb;
proxy_redirect off;
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
}
}
But with this config, when one of 2 backend server is down, nginx still routes request to it and it results in timeout half of the time :(
Is there any solution to make nginx to automatically route the request to another server when it detects a downed server.
Thank you.
Are there any production-quality iSCSI SANs suitable for use with Windows Server 2008/SQL Server for failover clustering?
So far, I've only seen Dell's MD3000i, and HP's MSA 2000 (2012i), which both are around $6K with a minimal disk configuration. Buffalo (yea, I know), has a $1000 device with iSCSI support, but they say it will not work for 2008 failover clustering.
I'm interested in seeing something suitable for failover in a production environment, but with very low IO requirements. (Clustering, say, a 30GB DB.)
As for using software: On Windows, StarWind seems to have a great solution. But it's actually more money than buying a hardware SAN. (As I understand, only the enterprise edition supports having replicas, and that's $3000 a license.)
I was thinking I could use Linux, something like DRBD + an iSCSI target would be fine. However, I haven't seen any free or low-cost iSCSI software that supports SCSI-3 persistent reservations, which Windows 2008 needs for failover clustering.
I know $6K isn't much at all, just curious to see if there are practical cheaper solutions out there. And finally, yes, the software is expensive, but many small business get MS BizSpark, so the Windows 2008 Enterprise / SQL 2008 licenses are completely free.