website fault tolerance

[somthing.random (Micah)]

Just wondering if anyone can clue me in on this, how does one provide a webserver with a redundant link. Suppose I run a website from home and my ISP has issues because someone cut through a cable, now my site is no longer accessible via my adsl link and my surfers get "page not found". If I had a second link in, say - cable, how would I effect the changeover.

I can think of two ways to do this, but I am really interested to know if there is a standard.

1. Routing.

I manage to convince both ISP to add the relevent routes into their routers routing tables. My home routers are also configured accordingly. Scenario still fails when my main ISP is completely down, since backup routes will never be seen by the surfer.

2. Dynamic DNS updates. Some kind of server at my home detects that main link is down and logs into DNS server and changes the IP that my website points to. TTL on A record is set to a very low level to effect a quick update. Home routers configured accordingly. Seems messy and a small amount of downtime is involved.

I'm not actually running a website from home, just curious as to the technologies at play. Can anyone explain how large websites handle a link down and seamlessly failover?

Thanks

[mswhin63 (Malcolm)]

I think these questions are better answered on a IP based forum. Try Whirlpool as they have quite an extensive IP based forum.

[multiweb (Marc)]

If you have one physical connection to your web server (at home) and the connection gets severed then there is no way. If you have two providers with two separate physical lines then the second would provide redundancy. At the end of the day your IP (static) is not dependent on the hardware that connects you to the internet (uplink).

What you mentioned with routing and other things. You can have multiple servers located in separate geographical locations and run what's called a round robin DNS. That would be what most companies do these days. But you have separate physical locations.

[OzRob (Rob)]

If you want redundancy you may want to look at cloud hosting as a solution.

[mithrandir (Andrew)]

You buy your own IP block, pay the two ISPs to provide BGP service for you, ensure the ISPs have different uplinks, and have a BGP capable router.

Or have some service provider do all that hard work for you.

[mswhin63 (Malcolm)]

I have a Dual WAN Router I wish to sell, just getting it checked and making sure all the gear is together.

[somthing.random (Micah)]

Thanks Mithrandir, BGP is pretty much the answer I was looking for. Round Robin DNS, while being a much easier implementation falls over when one of the links goes down due to DNS cacheing issues, still good to know

[tlgerdes (Trevor)]

For a home setup DynDns with a dual link router or 2 seperate links is your answer. No ISP is going to let you run BGP over am ADSL or consumer grade service. Plus you will need a whole lot more comms gear that makes it not worth it.