Reflex
Datadog Labs Rust library for observability control loops where Jev recommends an action and declared guards decide if it commits.
Overview
Reflex is a Rust library from Datadog Labs for control loops that act on observability data. Metrics queried from Datadog and forecasts from Toto become typed state, a judge such as TypeSafe's Jev recommends an action, and an executor commits it only if the state machine's legality checks, guards and invariants hold. Optional effects then perform external work. Target uses are circuit breaking, scheduling, autoscaling and retries, where the right action depends on changing conditions but execution must obey fixed constraints.
The included simulator shows a gateway with Catalog, Payments and Search circuits. Every 10 seconds Jev returns Open, Probe or NoChange per service, carrying the Datadog evidence and timestamps it saw and the circuit revision it applies to. Reflex rejects the action if the circuit changed meanwhile, the evidence is stale or missing, or the 10-second execution deadline has passed, and it enforces cooldowns and a five-probe close. The simulator also includes a resource scheduler and cluster autoscaler, and Reflex emits OpenTelemetry counters and spans. It is not the same project as other entries named Reflex.
What the decision model decides
| Type | Question | Answers |
|---|---|---|
| Choice | Should this service's circuit open, probe, or stay unchanged? | Open · Probe · NoChange |
How it works
- Query Datadog metrics and Toto forecasts into typed state
- Jev recommends a typed action with its evidence attached
- Executor checks the transition's guard (freshness, cooldown, probe limits) and invariants
- Commit a verified state transition or reject it with a reason
- Emit OpenTelemetry spans for evaluations and transitions
Strengths
- Model output cannot violate declared invariants
- Stale or out-of-date recommendations are rejected
- Every decision is inspectable with its evidence
Caveats
- Demonstrated in a simulator rather than production traffic
- Licence not stated in the fetched README
At a glance
- Type
- Library
- Status
- prototype
- Language
- Rust
- Runtime
- Rust library + simulator
- Has code
- yes
Use cases and integrations
How curated lists describe it
Rust library for control loops over observability data: metrics and forecasts become typed state, a model recommends an action, and it is committed only if the guards and invariants you declared hold. Not the same project as the open model of the same name.
MrJev/awesome-jev
Frequently asked questions
What does Jev decide?
In the circuit-breaker example, whether each service's circuit should open, probe or stay unchanged.
Can Jev force an unsafe transition?
No; Reflex commits the action only if the guards and invariants pass.
Is this related to the open model named reflex?
No, it is a different project.
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