Broker Gateways, Service Meshes, and Event Reliability

A multi-provider quantum platform eventually becomes a brokered system. Users should not hard-code every provider API, queue policy, or evidence convention. The broker exposes a stable operating contract, then routes to providers, simulators, reservations, and internal services.

Gateway and service-mesh patterns are useful references. Kubernetes Gateway API is an official Kubernetes project for expressive, role-oriented L4/L7 routing [R235]. Envoy describes itself as a high-performance distributed proxy and universal data plane for service mesh architectures [R236]. Quantum platforms can adapt these ideas, but must treat scientific semantics as part of routing.

flowchart LR
    User[User or service] --> Gateway[Quantum gateway]
    Gateway --> Auth[Identity and policy]
    Auth --> Broker[Quantum broker]
    Broker --> ProviderA[Provider A]
    Broker --> ProviderB[Provider B]
    Broker --> Simulator[Simulator]
    Broker --> Evidence[Evidence pipeline]

Quantum gateway responsibilities

flowchart TB
    Request[Workload request] --> Validate[Validate contract]
    Validate --> Authorize[Authorize]
    Authorize --> Route[Route]
    Route --> Execute[Execute]
    Execute --> Observe[Trace and events]
    Observe --> Evidence[Evidence]

Service mesh fit

A service mesh can help with identity propagation, retries, mTLS, traffic splitting, and telemetry between platform microservices. It cannot decide whether a QAOA result is scientifically acceptable. Keep scientific policy in the quantum broker and evidence layer.

flowchart LR
    Mesh[Service mesh] --> Transport[Transport reliability]
    Mesh --> MTLS[mTLS and identity]
    Mesh --> Traces[Traces]
    Broker[Quantum broker] --> Semantics[Scientific routing]
    Broker --> Policy[Quantum policy]
    Broker --> EvidenceRules[Evidence rules]

Event reliability

Quantum systems produce events that must not silently disappear: admission decisions, provider job IDs, result availability, evidence signatures, advisory matches, and claim status transitions.

sequenceDiagram
    participant Broker as Broker
    participant Bus as Event bus
    participant Store as Durable store
    participant Evidence as Evidence service
    participant Relay as Outbox relay
    Broker->>Store: atomically persist workload state and outbox event
    Relay->>Store: read committed outbox event
    Relay->>Bus: workload.admitted with stable event ID
    Bus->>Evidence: deliver event, possibly more than once
    Evidence->>Store: atomically deduplicate and persist evidence ID

Commit workload state and its outbox event together, then relay committed events and deduplicate consumer effects. For submission retries, retain the provider idempotency token where supported and reconcile ambiguous responses against provider job IDs before resubmitting. Local deduplication alone cannot guarantee exactly-once QPU execution or billing across a provider boundary. Transactional outbox pattern; Braket submission API.

Routing semantics

flowchart TB
    Route[Route decision] --> Fidelity[Fidelity requirement]
    Route --> Queue[Queue and deadline]
    Route --> Cost[Cost policy]
    Route --> Governance[Governance policy]
    Route --> Evidence[Evidence requirement]

Backpressure

Backpressure protects scarce resources and trust pipelines.

flowchart LR
    Load[High load] --> Detect[Detect saturation]
    Detect --> Shed[Shed low-priority work]
    Detect --> Delay[Delay non-urgent jobs]
    Detect --> Reserve[Protect reservations]
    Detect --> Alert[Alert owners]

Backpressure should distinguish between broker saturation, provider queue saturation, evidence lag, and budget exhaustion. Each has different remediation.

Operating rule

Route by contract, not by convenience. A provider route is acceptable only when it satisfies the workload’s target, evidence, budget, and governance constraints.