Canary release strategy vs. Blue/Green

Question

My understanding of a canary release is that it's a partial release to a subset of production nodes with sticky sessions turned on. That way you can control and minimize the number of users/customers that get impacted if you end up releasing a bad bug.

My understanding of a blue/green release is that you have 2 mirrored production environments ("blue" and "green"), and you push changes out to all the nodes of either blue or green at once, and then use networking magic to control which environment users are routed to via DNS.

So, before I begin, if anything I have said so far is incorrect, please begin by correcting me!

Assuming I'm more or less on track, then a couple of questions about the two strategies:

• Are there scenarios where canary is preferred over blue/green, and vice versa?
• Are there scenarios where a deployment model can implement both strategies at the same time?

Answer 1

I have written a detailed essay on this topic here: http://blog.itaysk.com/2017/11/20/deployment-strategies-defined

In my opinion, the difference is whether or not the new 'green' version is exposed to real users. If it is, then I'd call it Canary. A common way to implement Canary is regular Blue/Green with the addition of smart routing of specific users to the new version. Read the post for a detailed comparison

Blue/Green:

Canary:

Answer 2

Blue-green releasing is simpler and faster.

You can do a blue-green release if you've tested the new version in a testing environment and are very certain that the new version will function correctly in production. Always using feature toggles is a good way to increase your confidence in a new version, since the new version functions exactly like the old until someone flips a feature toggle. Breaking your application into small, independently releaseable services is another, since there is less to test and less that can break.

You need to do a canary release if you're not completely certain that the new version will function correctly in production. Even if you are a thorough tester, the Internet is a large and complex place and is always coming up with unexpected challenges. Even if you use feature toggles, one might be implemented incorrectly.

Deployment automation takes effort, so most organizations will plan to use one strategy or the other every time.

So do blue-green deployment if you're committed to practices that allow you to be confident in doing so. Otherwise, send out the canary.

The essence of blue-green is deploying all at once and the essence of canary deployment is deploying incrementally, so given a single pool of users I can't think of a process that I would describe as doing both at the same time. If you had multiple independent pools of users, e.g. using different regional data centers, you could do blue-green within each data center and canary across data centers. Although if you didn't need canary deployment within a data center, you probably wouldn't need it across data centers.