Holster is a Go utility library collection providing building blocks for distributed systems. It offers deterministic time control for testing, leader election implementations (etcd-based and Raft-inspired), enhanced error handling with context and stack traces, service discovery (Consul, DNS SRV), OpenTelemetry tracing, caching mechanisms (LRU, TTL, ExpireCache), retry utilities, HTTP request signing, gRPC connection pooling, and MX record resolution. Designed as drop-in replacements for standard library components with enhanced functionality, it focuses on solving common infrastructure challenges in microservices architectures. The library maintains a clear separation of concerns with each package addressing a specific cross-cutting concern.