July 2018
Intermediate to advanced
506 pages
16h 2m
English
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Health checks
In addition to member instances, target pools may be configured to use health checks, which periodically probe instances to determine the health of each instance within the target pool. With a health check configured, load balancers will only direct traffic to instances that are considered healthy. For NLBs, health checks take the form of HTTP requests to a specified URL and port. An instance is considered healthy if it responds with an HTTP status code 200. This has a few advantages:
- Dramatically reduces the number of failed requests due to server errors
- Instances do not receive traffic before they are fully operational
- Instances can be made to report as unhealthy before being removed from the target pool, in which case the ...