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I would like to know how these companies deploy new versions of their sites without downtime. I am aware of the BlueGreenDeployment model, however, I would like to know what these sites do to avoid/minimize downtime.

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I believe BlueGreeDeployment model is primarily meant to handle deployments of new systems. Its not meant to handle redundancy. –  wag2639 Jun 30 '10 at 2:40
    
@wag2639: we are discussing deployment, not redundancy. But some redundancy methods are very useful during deployment to present a seamless user experience. –  Chris S Jun 30 '10 at 15:57

3 Answers 3

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Google handles it in a few different manners. If you study their data center model, and the fact that they run 'clusters' of machines in each data center, they are able to shut down a data center so that it doesn't take requests, roll out the changes, turn on the data center, and do rolling upgrades. They can also do this with the clusters within a data center. Recently they upgraded the filesystems on their machines from ext3 to ext4 in-place by rolling things out on a per data center basis.

Google also does staged rollouts where clusters of people get different user experiences than other users. Facebook does this as well.

Ebay decommissions a large portion of their data center through load balancer changes, upgrades and migrates over decommissioning the other half. It has been said that they have enough redundancy to run their site on 1/3 of their available hardware. They may have more sophisticated methods now, this was a paper I read about 4 years ago.

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Websites as large as Google and eBay use much more complicated methods of serving their websites than the model presented in your Blue-Green link. There are proxy servers, failover hardware (or emulators), anycast, and many other technologies which keep things running seamlessly.

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Usuall by having multiple servers behind load balancers that handle the sites. In this way they can remove some servers from the load balancer to upgrade and then put them back into rotation and take out the others and upgrade them. In this manner the site never appears to go offline.

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