+-------------------------+-------------+------------------------+
| Deployment Strategy | Instance | Blue/Green, Rolling |
+=========================+=============+========================+
| Testing Strategy | User | Canary, A/B, Shadow |
+-------------------------+-------------+------------------------+
Deployment Strategy
1. Blue/Green pattern
- Having two identical environments: V1 and V2, where both V1 and V2 are running, but only V1 has all traffic while V2 is in testing.
- V2 is released alongside V1, and traffic is routed to V2 after testing
- The load balancer will direct traffic between two environment
- Zero downtime and instant rollback
- Cost is high to maintain two environments and might lose use session during routing changes between versions.
To apply Blue/Green deployment strategy is fairly easy with Google App Engine platform, where it was build in with “Split Traffic” feature. If you are not very familiar with App Engine, I have this article demo deploying a Flutter WebApp on App Engine.
First you need a minimum of two versions of the application in App Engine.
Click “Split Traffic” button to enter the config page:
Now watching traffic being diverged with either version 1 or 2 of your WebApp
2. Rolling update pattern
- Slowly replacing the current running V1 instance with the new version, until V1 is completely moved after V2 has passed a health check.
- At any given time, there is always an N+1 instance running, because the actual deployment occurs over a period of time.
- Because V1 and V2 co-exist, users might be routed to both versions, so having V2 backward compatible is very important.
- Zero downtime and low risk
Testing Strategy
3. Canary pattern
- V2 is release alongside the Production version V1, but only to a small group of users, followed by a full rollout.
- Use load balancer to split a percentage of traffic from Prod to Canary
- Able to test live production traffic with zero downtime and fast rollback
Similar to Blue/Green deployment strategy, if you are using Google App Engine, you can try this testing strategy using the “Split Traffic” feature, instead of switching traffic all at once, you can diverge a small percentage from V1 to V2.
4. A/B pattern
- Both V1 and V2 are released to users.
- Help businesses to make decisions with collective data. It is beneficial when there are multiple implementation options for one set of features to decide which one is more effective.
- Complex validation metric
5. Shadow pattern
- Both V1 and V2 are released to users.
- V2 will receive real traffic, but features are hidden from users
- It won’t impact users on V2 as their requests are the same
