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High Availability (HA), multiple servers, multiple data centers, multiple providers, DNS failover etc etc.
Usually HA, Load Balancing, multiple providers in diff countries to ensure speed (& in case of emergency, somewhere to handle the excess traffic being directed there)
Dont put all your eggs in one basket .
If you only host static content or a few PHP/HTML pages it's pretty easy. I use Sucuri for "loadbalancing". It always checks if my main IP is responding - if it starts responding slow or goes offline it just put my backup server as main.
It will get more complicated if you have databases and other applications.
Its all about how much money you willing to burn.
This is one of those situations you can mark availability levels (90%, 99%, 99.9%, etc.) on one axis, cost/difficulty on the other, and draw an exponent function graph.
That is to say, 90% is easy/cheap, 99% is pretty easy/pretty cheap, 99.9% is expensive/hard, 99.99% is very expensive/very hard, 99.999% is extremely expensive/extremely hard, etc.
Skeptics would say that the curve asymptotically approaches 100% but never quite reaches it...
I happen to run such a service and can tell you some things (which in one way or another have already been hinted at here).
Besides proper dns the "secret sauce" is in a) wise choice of DB, proper conception (and of course configuration) and b) good choice of hosting providers (which is an art in itself), and c) (in our case) a custom web server. The "custom" however is for security purposes not for being reliable and resilient; that is achieved by multiple cross-synchronizing front-ends as well as a shadowed back-end. From what I can see so far that whole system is beyond 4/9 and on a good way to 5/9 (99.999%). But again, our focus was/is on security and while resilience/availability is important we didn't expressely strive for anything beyond 4/9.
Custom, as in "I built it from scratch"? If so, I wouldn't say that's a plus on the secure part
If by custom, you mean "compiled only what's needed into it", I agree.
The world of formally verifiable software is a rather different one from some C or php hacking. Translating it into the normal world one might say that we used a (well tested and verified) library for the foundation.
But yes, custom built and compiled, not scripted.
The whole concept and custom building it also allows for some other desirable gadgets like the site being able to survive a "slashdot tsunami" and generally quite extreme load spikes or feeding offenders directly into the edge firewall. Another very important goal of the client was to not have any data of his customers online; any vital data are encrypted at all times except for the few microseconds when they are actually needed/processed.
"slashdot tsunami"
Slashdot tsunami in the old days; now its slashdot trickle and Reddit tsunami.
OK, you got me. I don't care about all those social services or about slashdot, reddit, etc. and "slashdotted" is somewhat of a established term for "massive load spike"
Slashdot is still around? I'll do a Lycos search in my Netscape Navigator and surf the information superhighway over there.
@raindog308
Bragger! Lycos? altavista not good enough for Mr. always-the-newest, huh? *g
altavista is dead.
Easiest way to do this would simply be to just use cloud flare. Its free, try it out! There are better options as stated above but cloudflare is hands down the easiest.
Impossible. I have it in my Viola bookmarks.
You must be one them hypermodern people who use 33 K modems because 9.6 is not fast enough for their bloated modern Mosaic browsers.
One thing is sure: No bloat-crap on my Vax!
No, using (or recommending) CloudFlare is a terrible idea. It also isn't going to do jackshit for the availability of a dynamic site.
Please read what I have said, I said there are better options but cf is the easiest. No need to come after me when I am merely showing options.
Except it isn't the easiest, because it doesn't actually do what the OP asked.
Please don't turn this thread into an argument but cf does have an always online feature that does work (I've used it before)
.
That's the ugly part. One might, for instance, anycast. The problem though is that the machines must update each other or else one is playing lottery.
I have a hint for anyone who is really interested and has the knowledgable people to pull it off: You want to avoid tcp and go sctp instead to keep the front-ends cross-updated and to connect them to the back-ends.
@cam246 Are you okay? CloudFlare does not provide HA. HA is when you have MULTIPLE systems setup so if one fails, it fails over onto the remaining system(s).
Yes, CloudFlare has an "Always Online" feature, but it does not help when there is a notice from CloudFlare saying that your site is down and displaying content cached hours ago. Dynamic sites don't work well with the Always Online feature anyway, so throw that off the list, you smart alec.
Always Online doesn't work for anything other than static content, which means it doesn't give you high availability unless your website is 100% static (which neither you nor the OP specified, and isn't true for most sites). Hence, a recommendation for CloudFlare doesn't really answer the question that's asked, other than in very narrow circumstances.
(Aside from that, Always Online doesn't work reliably either, and it's a bit of a mystery when CF empties their caches.)
You can set when cf empties their cache in the settings.
I hope this finally clears up where I was coming from.
Thank you both for being so closeminded in my suggestion. I use cf and it will save a static copy of any type of site. Like people have stated many times it won't work for everything which I agree with as I said in my OP
In my experience, this does not work reliably. Caches are also isolated to a PoP, so if a given page was never visited by somebody through a given PoP (since it last expired), that PoP will not have a copy of it. And so on.
Interesting I haven't had that problem. I will do some tests of my own to see if it's still like that. If so that's not good..... I'll let you know when I have time later today. Thanks for telling me this.
Thank you for clarifying
Yeah, I'll admit that I jumped to a conclusion. Another tip: CloudFlare Always Online always f*cks itself up when there's AJAX. I've tried it on my site before, and the main area (loaded via/ an AJAX request) ended up just showing a 522 error.
No hard feelings!
Ahh ok thanks. I'm gonna do my test on some of my websites to see how reliable it is. I was under the impression that they had made it pretty much bulletproof I guess I'll find out how well it works for my sites.
No hard feels as always