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Patterns for Resilient Architecture — Part 3
Preventing service failures with health checks
What are we talking about?
In part 1, I discussed how to architect resilient architectures using the principle of redundancy, which is the duplication of components of a system in order to increase the overall availability of that system.
Such a principle implies that you use a load balancer to distribute network or application requests across a number of server instances. In order to determine whether a downstream server instance is capable of handling a request successfully, the load balancer uses health checks.
Health checks gather both local and dependency information in order to determine if a server instance can successfully handle a service request. For example, a server instance might run out of database connections. When this occurs, the load balancer should not route requests to that server instance, but instead, distribute the service traffic to other available server instances.
Health checks are important because if you have a fleet of 10 server instances behind a load balancer, and one of them…
