CONCEPT Cited by 1 source
Critical User Journey (CUJ)¶
A Critical User Journey (CUJ) is a user-workflow-centric design primitive: the full end-to-end sequence of steps a user takes to accomplish a business-critical task, described without reference to the underlying systems.
Originating in Google SRE practice, CUJs are the counterpart to SLOs at the product-design altitude — SLOs measure "is the service healthy enough?", CUJs measure "can the user still complete their goal?" The architectural payoff: when CUJs are the primary design target, systems can be re-architected underneath without disrupting user workflows — interface stability (see below) becomes the load-bearing property.
As a platform-design primitive¶
For infrastructure platforms specifically, designing around CUJs (rather than around storage layers / ingestion pipelines / query engines) produces architectures where:
- Users don't change tools — existing dashboards, alerting rules, ad-hoc queries, and IDE integrations keep working.
- Platform can swap substrates freely — the team can move data between storage tiers, switch query engines, refactor ingestion pipelines, without user-visible disruption.
- Migrations happen in-place — new capabilities land as invisible extensions of existing CUJs, not as parallel new systems the user has to adopt.
Load-bearing property: interface stability¶
The CUJ discipline pushes teams to treat the user-facing interface as the stable contract and everything below it as fungible. Concrete instance at Hydra: the CUJ is "engineer investigates an incident using Grafana + PromQL", so the storage substrate can be a lakehouse (not a TSDB), queried via a PromQL-to-SQL translation layer — invisible to the user.
Seen in¶
- sources/2026-05-05-databricks-10-trillion-samples-a-day-scaling-beyond-traditional-monitoring — canonical instance at the observability-platform design altitude. "Building Hydra was not just an infrastructure challenge; it was an interface design challenge. From the beginning, we designed Hydra around Critical User Journeys (CUJs) for our engineers rather than around storage layers or ingestion pipelines. Our goal was simple: engineers should be able to work with high-cardinality metrics using the same interfaces they already rely on."