servicedepends

Servicedepends is the concept that describes the relationships between services in a system, indicating which services must be available for another service to operate correctly. It is a key aspect of service orchestration, deployment manifests, and runtime management in many architectures, including monolithic, microservices, and containerized environments. The core idea is to model dependencies as a graph where edges point from a dependent service to its prerequisites. This graph guides startup order, health checks, failure handling, and scaling decisions.

Dependencies can be hard or soft. A hard dependency requires the other service to be up and healthy for the dependent service to function, while a soft dependency provides optional capabilities or performance benefits. Version constraints, environment-specific requirements, and runtime states may also be part of a servicedepends specification.

Common ways to express servicedepends vary by platform. System managers like systemd use directives such as Requires and After to enforce startup order. Container orchestration platforms model dependencies via readiness probes, init sequences, and declarative manifests; Kubernetes, for example, relies on health checks and coordination patterns rather than strict startup order. Docker Compose allows depends_on to influence startup sequences, though it does not guarantee immediate readiness.

Implementing effective servicedepends involves cycle detection, proper error handling, and resilience strategies, such as timeouts, retries, and circuit breakers. Design best practices include keeping dependencies explicit, avoiding tight coupling, implementing idempotent startup procedures, and favoring asynchronous decoupling where possible. Challenges include circular dependencies, version skew, and cascading failures across services.

See also: service discovery, health checks, orchestration, and service mesh.