Resilience4j is a lightweight fault tolerance library inspired by Netflix Hystrix. We like its lightweight and modular structure where we pull in specific modules for specific capabilities such as circuit-breaking, rate-limiting, retry, and bulkhead. While service meshes are taking on some of the fault tolerance capabilities, fault tolerance libraries continue to remain a key component of our systems for more nuanced domain-specific fault tolerance behavior and for non-containerized services. With Hystrix going into maintenance mode, Resilience4j becomes a default choice in the Java ecosystem. It can work with synchronous APIs as well as reactive ones. It also surfaces metrics to dropwizard metrics, Prometheus and others using additional modules.