Blue Green Deployment Strategy.md

title	notetype	date
Blue Green Deployment Strategy	feed	16-08-2022

Blue/Green is a [[Deployment Strategy]] where version B is deployed alongside version A, after which the traffic is switched from A to B.

How it works

• before we start, we have 2 instances of A running and serving traffic
• we deploy 2 instances of B alongside them, which are still not serving any traffic
• we confirm that version B deployment looks good
• we switch traffic flow from version A to version B on [[Load Balancer]] side

Tradeoffs

Pros:

• zero downtime
• instant rollout and rollback
• entire application is changed in one go, no different api versions running at the same time

Cons:

• it expects us to run 2 identical environments alongside one another, which can be expensive
• it doesn't make much sense to run two databases, so you have to figure out how to run both versions connected to a single database (backwards-compatible db updates, decoupled db migrations from application deployment)

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Status: #💡

References:

• Six Strategies for Application Deployment