<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On 6 Nov 2008, at 13:57, Simon Perry wrote:</div><blockquote type="cite"><div>I need to come up with a hosting solution for a new site that offers <br>100% uptime but not having done this before I don't know what solutions <br>are available? What I have come up with so far is;<br><br>1) Two dedicated servers in separate data centres with a 3rd party round <br>robin DNS service</div></blockquote><div><br></div><div>If you're serious about this, at least pick two different hosting providers for the data centers.</div><div><br></div><div>I've experienced:</div><div> - hosting providers going bankrupt, forcing us to move servers at a days notice (dot com bubble... Luckily we *didn't* rely on a single provider)</div><div> - hosting providers that turn out to have systemic problems with the way they handle hardware or software upgrades that affect multiple of their sites at once, meaning the disaster recovery site would fail at the same time as the primary far more than you should expect.</div><div> - hosting providers who route all their outbound traffic from multiple data centres through the same network path, so failures with their network providers make everything fail at once.</div><div><br></div><div>Also consider that for two data centres to provide full failover you need at least twice the equipment needed to run the site - each data centre must be able to take the full load. If traffic is high enough going for three sites can be a cheaper alternative as it allows you to "only" have 50% extra capacity for each site and still be able to handle a full site failure (the tradeoff is a slightly higher risk of having to do a failover, of course, as you now have three sites that can fail).</div><div><br></div><div>DNS round robin is not entirely reliable, though providers like UltraDNS / Neustar do a decent (but expensive) job of handling failover. The problem is that you'll find many people cache DNS entries longer than they are supposed to. You *will* be unavailable to many people for at least a few minutes in the case a single site fails if you use DNS. If this is not acceptable your only real choice if you want to do it all yourself is to set up BGP (or have an ISP do it for you) so you can announce multiple routes and have both sites answer to the same IP. You may still get "blips" when the site fails over, but they can be made a lot shorter.</div><div><br></div><div>If your content is mainly static, you can sidestep (part of) the problem by using a content distribution network such as Panther Express which can be set up to cache everything that has been requested from your site more or less permanently (as a bonus you get geographic load balancing that can significantly speed up access from outside the UK - in one case I was testing Panther with a company I worked for and they served up content to our test script faster than our web server located on the local host). Most of these will use BGP to announce multiple routes, and so will be very reliable if well managed. Some of them can also be set up to talk to multiple backends at your end, so that _they_ handle the load balancing / failover between your sites. They are at best problematic for dynamic content though, as they are geared towards longer term caching.</div><div><br></div><div>Keep in mind that some data centres - especially smaller ones - in the London area are also vulnerable to failures in core infrastructure in Docklands - ask hard questions about where they get their connectivity. You might find both the data centres you pick get all their bandwidth from the exact same locations (one of the peering points in Docklands, typically - if you're extra unlucky they may be going via the same fibre bundles), and while the big peering points are typically very reliable there are enough alternatives that have backup paths that doesn't go via Docklands that there's no need to take the chance if the uptime is that critical to you.</div><div><br></div><blockquote type="cite"><div>2) A managed redundant hosting solution. Can anyone recommend a supplier?<br></div></blockquote></div><div><br></div>I don't know anyone that sells this as a "packaged" solution, due to all the data synchronization issues and complexities the moment dynamic data is involved that other people have pointed out - those issues tend to be very application specific.<br><div apple-content-edited="true"> <span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><br class="Apple-interchange-newline">-- </div><div>Vidar Hokstad</div><div>Technical Director</div><div>Aardvark Media Limited</div><div><div><br></div></div></div></span></div></body></html>