How can I detect and survive being “Slashdotted”?

问题:

What's a good way to survive abnormally high traffic spikes?

My thought is that at some trigger, my website should temporarily switch into a "low bandwidth" mode: switch to basic HTML pages, minimal graphics, disable widgets that might put unnecessary load on the database, and so-on.

My thoughts are:

• Monitor CPU usage
• Monitor bandwidth
• Monitor requests / minute

Edit: I am familiar with options like caching, switching to static content or a content delivery network, and so on as a means to survive, so perhaps the question should focus more on how one detects when the website is about to become overloaded. (Although answers on other survival methods are of course still more than welcome.) Lets say that the website is running Apache on Linux and PHP. This is probably the most common configuration and should allow the maximum number of people to gain assistance from the answers. Lets also assume that expensive options like buying another server and load balancing are unavailable - for most of us at least, a mention on Slashdot is going to be a once-in-a-lifetime occurrence, and not something we can spend money preparing for.

回答1:

1. Don't give anyone the URL
2. Build something so useless that if rule 1 gets broken nobody will come anyway.

回答2:

1. install munin to monitor load/memory consumption etc and notify on overloads.
2. install monit to restart apache2 if it crashes
3. install nginx as apache2 frontend, it will massively decrease memory requirements under heavy load

回答3:

It's worth mentioning that clever caching and low bandwidth modes will be useless if you simply don't have enough bandwidth on your connection, so make sure the connection to your server is fat enough. Don't host it on your home DSL connection, for example.

I speak from experience of being slashdotted. It's not fun when you can't access the Internet at all because thousands of people are simultaneously trying to download photos of a computer your housemate mounted inside a George Foreman grill. No amount of firewalling will save you.

回答4:

The basics:

1. Don't try to host high-volume sites on Windows unless you are a true Windows guru. It can be done, but it's a time versus cost issue.
2. Use static content (i.e., no database queries) everywhere you can.
3. Learn about cache-control headers and use them properly for images and other static assets.
4. At the very least, use Apache, but if you can, use lighttpd or another high-performance webserver.

The real answers:

1. Really know your SQL, and spend time analyzing slow queries. Most page loads shouldn't require more than a second of straight queries.
2. Determine where your load really is. If it's a media-heavy site, consider hosting content elsewhere (like Akamai, or some other service). If it's a database-heavy site, consider replication.
3. Know what kind of replication will work for you. If you have a read-heavy site, standard MySQL master/slave replication should be fine. If you have a lot of writes going on, you'll need some kind of multi-master setup, like MySQL Cluster (or investigate 'cascading' or 'waterfall' replication).
4. If you can, avoid calling PHP - i.e. have a cached static (HTML) copy of the page (which is what most of the Wordpress caching plugins do). Apache is much faster serving static files than even the simplest hello world PHP script.

回答5:

Here's a rather lengthy but highly informative article about surviving "flash crowds".

Here's their scenario for the situation their proposed solutions address:

In this paper, we consider the question of scaling through the eyes of a character we call the garage innovator. The garage innovator is creative, technically savvy, and ambitious. She has a great idea for the Next Big Thing on the web and implements it using some spare servers sitting out in the garage. The service is up and running, draws new visitors from time to time, and makes some meager income from advertising and subscriptions. Someday, perhaps, her site will hit the jackpot. Maybe it will reach the front page of Slashdot or Digg; maybe Valleywag or the New York Times will mention it.

Our innovator may get only one shot at widespread publicity. If and when that happens, tens of thousands of people will visit her site. Since her idea is so novel, many will become revenue-generating customers and refer friends. But a flash crowd is notoriously fickle; the outcome won't be nearly as idyllic if the site crashes under its load. Many people won't bother to return if the site doesn't work the first time. Still, it is hard to justify paying tens of thousands of dollars for resources just in case the site experiences a sudden load spike. Flash crowds are both the garage innovator's bane and her goal.

One way out of this conundrum has been enabled by contemporary utility computing.

The article then proposed a number of steps the garage innovator can take, such as using storage delivery networks and implementing highly-scalable databases.

回答6:

I rewrite all URLs referred by several popular sites to be redirected through the coralCDN.

An example for Apache:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /

RewriteCond %{HTTP_USER_AGENT} !^Googlebot
RewriteCond %{HTTP_USER_AGENT} !^CoralWebPrx
RewriteCond %{QUERY_STRING} !(^|&)coral-no-serve$
RewriteCond %{HTTP_REFERER} ^http://([^/]+\.)?digg\.com [OR]
RewriteCond %{HTTP_REFERER} ^http://([^/]+\.)?slashdot\.org [OR]
RewriteCond %{HTTP_REFERER} ^http://([^/]+\.)?slashdot\.com [OR]
RewriteCond %{HTTP_REFERER} ^http://([^/]+\.)?fark\.com [OR]
RewriteCond %{HTTP_REFERER} ^http://([^/]+\.)?somethingawful\.com [OR]
RewriteCond %{HTTP_REFERER} ^http://([^/]+\.)?kuro5hin\.org [OR]
RewriteCond %{HTTP_REFERER} ^http://([^/]+\.)?engadget\.com [OR]
RewriteCond %{HTTP_REFERER} ^http://([^/]+\.)?boingboing\.net [OR]
RewriteCond %{HTTP_REFERER} ^http://([^/]+\.)?del\.icio\.us [OR]
RewriteCond %{HTTP_REFERER} ^http://([^/]+\.)?delicious\.com
RewriteRule ^(.*)?$ http://example.com.nyud.net/$1 [R,L]
</IfModule>

回答7:

There's simply no way to know whether or not your website will survive heavy loads unless you stress test it. Use something like siege and see where your performance problems lie. Does it grow in memory too quickly? Does it start slowing down with a bunch of concurrent connections? Does it start taking forever to access the database?

Once you know where the performance problems lie, then it becomes a matter of getting rid of them. Unfortunately, it's difficult to go into much more detail than that without knowing more about your particular situation, but keep in mind that you ARE talking about optimizations here. Thus, you should only act when you KNOW there are performance problems.

And I would argue that you're not necessarily just preparing for a once in a lifetime event. DOS attacks still happen, so it's good to have preparations in place even if your site doesn't get slashdotted.

The only thing that I can think of off the top of my head that will help you in almost all situations is if you gzip your content. That will save a lot of bandwidth and all modern browsers will support it without too much of a performance problem.

回答8:

The real question is "What is the single most effective way to be Slashdotted"

If it's a real problem, redirect the traffic to my site.

回答9:

I think the premise is wrong: you really really want to get slashdotted, otherwise you wouldn't have a web site in the first place. A much better question is how do you handle the extra traffic? And even that is really two questions:

1. How do you technically manage the additional server load?
2. How do you greet the new users, so that you can hopefully get some of them to stick around??

回答10:

Don't write content or provide a service that may appeal to geeks ;)

回答11:

Put it in the cloud!

This probably isn't relevant for personal blogs etc but for bigger sites cloud hosting will solve this. Amazon EC2 for example, thing about this strategy is that it will cost you a ton of money.

On a smaller scale, using a CDN for all your images/static content might help a bit too, again evaluating the price is important. Amazon S3 is the CDN i hear about the most.

回答12:

For sites that experience high traffic, Akamai is a good solution to make the site fast, extraordinarily scalable, and reliable in spite of your own infrastructure. Akamai is a service (not free) which will cache your site a locations around the world. At my last job, our e-commerce catalog was cached via them and our servers could go down and nobody would know unless they tried adding to their cart. Also, we had our image servers go down once and Akamai's caching saved us again.

回答13:

Never become popular.

While that will work, it's not real helpful. What you need infrastructure that can scale on very short. Something like Google Gears or Amazon's web services seems ideal for this, since even Slashdot's not going to overwhelm Google or Amazon. If you want your own server make sure your network provider isn't going to cut you off at any preset bandwidth limit. Buy enough hardware so that you're not straining just to carry your normal traffic without any slack to handle sudden spikes.

回答14:

There are a number of ways this can be done, or at least helped. Search Google for "slashdot-proof" and you'll find a number of them:

• Slashdot-proof your server with FreeCache - Boing Boing
• Simple Thoughts Blog is now Slashdot Proof

etc.

回答15:

Cache... hard. Record hits, and if a spike occurs, write out a completely static copy of the page being hit, then serve that. Cutting DB queries from 100 to 2 with a good caching system can survive a weak slashdotting, but having any DB queries at all will still result in a dead site under serious load that you aren't prepared for.

回答16:

Increase the level of caching from the DB so that the content might me slightly more out of date but faster accessed. Naturally, this only applies if the content does not have to be 100% consistent.

回答17:

You can also use Nagios to monitor the server health. Based on your requirements, at certain conditions, you can trigger an existing SQL file to switch modes for your website.

For example, add "UPDATE settings_table SET bandwidth = 'low';" into that SQL file and run it in mysql and do the opposite when the conditions get back to normal.

回答18:

nearlyfreespeech.net is a semi-cloud so to speak and helps a ton in situations like this. As others above mentioned, layered caching helps a lot. Pull chunks of information from memcached instead of the database, have a reverse proxy (or a distributed reverse proxy aka CDN, Panther Networks is cheap) in front of you.

回答19:

netstat -plant | awk '$4 ~ /:80\>/ {print}' | wc -l

This will show you all of the connections to the Apache server. You can create a cgi script that will calculate the total number of connections to the Apache service and issue a warning once it reaches a certain threshold. What to do at that point is another question.

Hopefully your server is prepared.

回答20:

Use caching!

If you're using WordPress (for example), you can use something like WP-Super-Cache. If you're using regular PHP there are still a number of options you can use including memcache. Or you can just use regular squid proxy style caching.

Any caching you use will help bulletproof (or slashdot/digg-proof) your site :-)

回答21:

I know with Digg you can contact them and request they blacklist your site. You can probably do the same with Slashdot.

回答22:

Make sure all pages you build are static, no database, and don't use images.

Actually, this place isn't doing THAT bad.

回答23:

Cache data.

Unnecessary Trips to database to display something that gets displayed the same every load is what kills a server. Write its output to a file and use that instead. Most CMSs and frameworks have caching built in (but you have to turn it on) but rolling your own is not the most challenging task.

回答24:

Auto-redirect to Coral CDN, unless the request is from coral cdn.

回答25:

There are a number of ways this can be done, or at least helped. Search Google for "slashdot-proof" and you'll find a number of them:

• Slashdot-proof your server with FreeCache - Boing Boing
• Simple Thoughts Blog is now Slashdot Proof

etc.

回答26:

.htaccess:

RewriteEngine on
RewriteCond %{HTTP_REFERER} slashdot\.org [NC]
RewriteRule .* - [F]

回答27:

One word: Knipex

回答28:

No one has mentioned load balancing... haproxy, etc. Optimize, cache and load balance should survive almost anything. That being said, I'm not sure if stackoverflow is behind a load balancer ;)

回答29:

About surviving you are right: switch or redirect the slashdotted link to a static html page without graphics. You might even want to put this page on an other webserver, so your original server will not take too much load.

I'd use a temporary redirection for this, and remove the redirection when the traffic wears off.

But how to detect this, this I'd like to know, too! Just counting the hits in the last few seconds might not be enough?

回答30:

Make sure your pages support Last-Modified & If-Modified-Since and/or ETag & If-None-Match headers. With these you can avoid many computations and transfers totally.

Search for HTTP conditional GET for more information.