What are blue-green deployment, Canary release and a/b test

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        Blue and green deployment 、A/B test 、 Release of canary , And grayscale publishing 、 Flow segmentation, etc , Often confused with , Affect communication efficiency . The fundamental reason is that these nouns often appear , People are familiar with it and can talk about it skillfully , There is no agreement on the understanding of these terms .

Here's from Blue-green Deployments, A/B Testing, and Canary Releases The definitions sorted out in .

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Blue and green deployment

The purpose of the blue-green deployment is Reduce the outage time when publishing 、 The ability to quickly retract releases .

It’s basically a technique for releasing your application in a predictable manner with an goal of reducing any downtime associated with a release. It’s a quick way to prime your app before releasing, and also quickly roll back if you find issues.

Blue and green deployment , There are two systems ： One is the system that is providing services , Marked as “ green ”; The other is the system to be released , Marked as “ Blue ”. Both systems are fully functional , And the running system , Only the system version is different from the external service .

first , There's no system , There is no difference between blue and green .

then , The first system was developed , Go online directly , There is only one system for this process , There is no difference between blue and green .

later , Developed a new version , To replace the old online version with the new one , Outside of the online system , Build a new system using the new version of code . Now , There are two systems running , The old system that is providing services to the outside world is the green system , The newly deployed system is the blue system .

The blue system does not provide external services , What to do ？

For pre release testing , Any problems found during the test , It can be modified directly on the blue system , Do not interfere with the system the user is using .（ Be careful , Only when the two systems are not coupled can they be guaranteed not to interfere ）

The blue system has been tested over and over again 、 modify 、 verification , After confirming that the online standard is met , Switch users directly to the blue system ：

For a period of time after switching , It's still blue and green , But the user has access to the blue system . Observe the blue system during this time （ New system ） Working state , If something goes wrong , Switch directly back to the green system .

When you are sure that the blue system for external services is working , When the green system that does not provide external services is no longer needed , The blue system has officially become an external service system , Become a new green system . The original green system can be destroyed , Release resources , To deploy the next Blue System .

Blue green deployment is just one of the online strategies , It's not a panacea for all situations . The premise that blue-green deployment can be implemented simply and quickly is that the target system is very cohesive , If the target system is quite complex , So how to switch 、 Whether the data of the two systems need to be synchronized and so on , You need to think about it .

BlueGreenDeployment The picture given in is particularly vivid ：

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Release of canary

Release of canary （Canary） It's also a publishing strategy , And what is often said at home Grayscale Publishing It's the same kind of strategy .

Blue and green deployment is to prepare two systems , Switching between two systems , The Canary strategy is that there's only one system , Gradually replace the system .

for example , The target system is a group of stateless Web The server , But it's a lot , Suppose there are 10000 .

Now , Blue and green deployment will not work , Because you can't apply for 10000 servers to deploy the blue system （ In the definition of blue-green deployment , The blue system needs to be able to take all the access ）.

One way to think of it is ：

Just a few servers , Deploy a new version of the system on it and test it . After passing the test , Worried about accidents , I don't dare to update all the servers immediately . First of all, we'll take 10 Update to the latest system , Then observe and verify . After confirming that there is no exception , Then update all the remaining servers .

This method is Release of canary .

More control can be done in practice , for example , For the original update 10 Set a lower weight for each server 、 Control is sent to this 10 Number of requests per server , Then gradually increase the weight 、 Increase the number of requests .

This control is called “ Flow segmentation ”, It can be used for Canary release , It can also be used in the back A/B test .

Blue green deployment and Canary release are two release strategies , Not everything . Sometimes both can be used , Sometimes only one of them can be used .

In the above example, you can use Canary , You can't use blue and green , So when can I use blue and green , You can't use canaries ？ When there is only one server in the whole system .

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A/B test

The first thing to be clear is ,A/B Testing and blue-green deployment and Canary , It's totally different .

Blue green deployment and Canary are release strategies , The goal is to ensure the stability of the new online system , It's about the new system BUG、 hidden danger .

A/B The test is the effect test , There are multiple versions of the service at the same time , These services are well tested , Services that meet online standards , There are differences, but there is no distinction between the old and the new （ They may have been deployed blue and green when they went online ）.

A/B The test focuses on the actual effect of different versions of the service , For example, conversion rate 、 Orders, etc .

A/B When testing , Running multiple versions of the service online at the same time , These services usually have some differences in experience , For example, page styles 、 Color 、 The operation process is different . By analyzing the actual effect of each version of the service , Choose the best version .

stay A/B In the test , Need to be able to control the distribution of traffic , for example , by A Version allocation 10% Of traffic , by B Version allocation 10% Of traffic , by C Version allocation 80% Of traffic .

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Reprint ： Blue and green deployment 、 Release of canary （ Grayscale Publishing ）、A/B The exact definition of the test By Li ji'ao Li Jiao's blog : Blue and green deployment 、A/B test 、 Release of canary , And grayscale publishing 、 Flow segmentation, etc , Often confused with , People are familiar with it and can talk about it skillfully , There is no agreement on the understanding of these terms .. Li ji'ao 、 Blue and green deployment 、AB test 、 Release of canary https://www.lijiaocn.com/%E6%96%B9%E6%B3%95/2018/10/23/devops-blue-green-deployment-ab-test-canary.html

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