Dependency blast radius

Definition

Dependency blast radius is the set of application functionality, data paths and user journeys that degrade or fail when a single external dependency degrades - including the parts that never call it directly, reached through shared workers, connection pools, queues and retry amplification.

The problem

The obvious blast radius is the feature that calls the dependency. The real one is larger: long-running calls hold connections and workers that unrelated features also need, so a partial upstream problem becomes a full application outage and produces an incident report naming the wrong component.

Why it matters

Blast radius is what makes a dependency a risk rather than a line item. It determines how much isolation an architecture needs, and it is usually discovered during an incident rather than designed for beforehand.

Practical example

A model provider degrades. Client timeouts hold sockets, retries multiply the load, queues grow, workers saturate - and the alert fires in a background job that never called the provider API, six hops from the cause.

How RELIASTRA approaches it

RELIASTRA keeps an independent, timestamped record of the dependency side of the timeline, so the outer edge of the blast radius can be correlated against the moment the dependency was independently observed failing rather than inferred from the alert that fired first.