Lab complete!
Now that you have completed this lab, make sure to update your Well-Architected review if you have implemented these changes in your workload.
Click here to access the Well-Architected Tool
What is the expected behavior? The previous time you simulated a complete failure of the RecommendationService
Now, with the new deep health check in place…
Refresh the web service multiple times
Refresh the health check URL multiple times
From the Target Groups console Targets tab note the health check status of all the servers (you may need ot refresh)
They all report unhealthy with http code 503. This is the code the deep health check is configured to return when the dependency is not available
Note the message at the top of the tab (if you do not see a message, try refreshing the entire page using the browser refresh function)
The Amazon Builders' Library: Implementing health checks |
---|
When an individual server fails a health check, the load balancer stops sending it traffic. But when all servers fail health checks at the same time, the load balancer fails open, allowing traffic to all servers. |
When we rely on fail-open behavior, we make sure to test the failure modes of the dependency heath check. |
A system set to fail-open does not shut down when failure conditions are present. Instead, the system remains “open” and operations continue. The AWS Application Load Balancer here exhibits this fail-open behavior and the service continues to serve requests sent to it by the load balancer.
Well-Architected for Reliability: Best practice |
---|
Implement emergency levers: These are rapid processes that may mitigate availability impact on your workload. They can be operated in the absence of a root cause. An ideal emergency lever reduces the cognitive burden on the resolvers to zero by providing fully deterministic activation and deactivation criteria. Example levers include blocking all robot traffic or serving a static response. Levers are often manual, but they can also be automated. |
Now that you have completed this lab, make sure to update your Well-Architected review if you have implemented these changes in your workload.
Click here to access the Well-Architected Tool