FedRAMP Moderate provider failover and degradation architecture for enterprise LLM — Reference Architecture

Reference architecture · published 2026-10-16 · regulated enterprise · FedRAMP Moderate · layout spec_first · implementation executed in CI before publish

Technical parameters

Every value below is a parameter you can hold a vendor or an internal team to. Adjectives are not acceptance criteria.

The control that resolves this is a Labelled Degradation Ladder, evaluated before the request reaches a model provider rather than audited afterwards. In regulated enterprise the binding constraint is FedRAMP Moderate, and the question it actually asks is which NIST 800-53 control does each component satisfy. The shape below holds p95 ≤ 600ms over REST over HTTPS, and ships with a standard-library implementation that runs as written.

The architecture friction point

When the primary provider degrades, traffic fails over to a weaker model and the answers keep flowing. Nobody downstream is told the quality changed, so the incident is discovered in complaints.

What FedRAMP Moderate specifically requires

FedRAMP is control-by-control. Every component must map to a specific NIST 800-53 Rev 5 control identifier with an implementation statement, and anything crossing the authorisation boundary needs its own justification in the SSP.

The artifact that satisfies it is a control implementation summary mapped to control identifiers. The way teams most often fail it: a component outside the authorisation boundary that nobody documented, found during assessment.

Implementation artifact — Degradation ladder with circuit breaker and quality floor

Standard-library Python, no external dependencies, runs as written. Executed by the publish gate: if it raises, this page does not ship. Wire it behind REST over HTTPS; the failure mode it guards against is a retried POST creating a duplicate record. The output you hand the assessor is the SSP control implementation summary.

"""Degradation ladder with a circuit breaker and labelled quality tiers.

The failure: a provider degrades, traffic silently fails over to a weaker
model, and nobody downstream knows the answer came from a lower tier. The
control is that degradation is explicit and labelled on the response, so a
consumer can refuse a tier it cannot accept, and that a failing provider is
taken out of rotation rather than retried into the ground.
"""
import time


class ProviderDown(Exception):
    pass


class CircuitBreaker:
    def __init__(self, threshold: int = 3, cooldown_s: float = 30.0):
        self.threshold, self.cooldown_s = threshold, cooldown_s
        self.failures, self.opened_at = 0, None

    def record_failure(self, now: float) -> None:
        self.failures += 1
        if self.failures >= self.threshold and self.opened_at is None:
            self.opened_at = now

    def record_success(self) -> None:
        self.failures, self.opened_at = 0, None

    def closed(self, now: float) -> bool:
        if self.opened_at is None:
            return True
        if now - self.opened_at >= self.cooldown_s:
            self.opened_at, self.failures = None, 0   # half-open: allow a probe
            return True
        return False


class Tier:
    def __init__(self, name: str, quality: int, call):
        self.name, self.quality, self.call = name, quality, call
        self.breaker = CircuitBreaker()


class DegradationLadder:
    """Tiers in descending quality. The response always names the tier that
    produced it; a caller declaring min_quality gets a refusal rather than a
    quietly worse answer."""

    def __init__(self, tiers: list):
        self.tiers = sorted(tiers, key=lambda t: -t.quality)
        self.events: list[dict] = []

    def complete(self, prompt: str, min_quality: int = 0, now=None) -> dict:
        now = now if now is not None else time.monotonic()
        attempted = []
        for tier in self.tiers:
            if tier.quality < min_quality:
                continue
            if not tier.breaker.closed(now):
                attempted.append({"tier": tier.name, "skipped": "circuit open"})
                continue
            try:
                text = tier.call(prompt)
            except ProviderDown:
                tier.breaker.record_failure(now)
                attempted.append({"tier": tier.name, "failed": True})
                continue
            tier.breaker.record_success()
            degraded = tier is not self.tiers[0]
            self.events.append({"tier": tier.name, "degraded": degraded})
            return {"text": text, "tier": tier.name, "quality": tier.quality,
                    "degraded": degraded, "attempts": attempted}
        raise ProviderDown(
            f"no tier at or above quality {min_quality} available: {attempted}")


if __name__ == "__main__":
    def primary(p): raise ProviderDown("502 from primary")
    def secondary(p): return f"secondary:{p}"
    def local(p): return f"local-small:{p}"

    ladder = DegradationLadder([
        Tier("frontier", 100, primary),
        Tier("secondary", 70, secondary),
        Tier("local-small", 30, local)])

    r = ladder.complete("summarise", now=0.0)
    assert r["tier"] == "secondary" and r["degraded"] is True, r
    assert r["attempts"][0]["failed"], r

    # A caller that cannot accept degradation gets an error, not a worse answer.
    strict = DegradationLadder([Tier("frontier", 100, primary),
                                Tier("local-small", 30, local)])
    try:
        strict.complete("x", min_quality=90, now=0.0)
        raise AssertionError("served below the declared quality floor")
    except ProviderDown:
        pass

    # The breaker opens after repeated failures and stops the retry storm.
    t = Tier("flaky", 50, primary)
    for i in range(3):
        try:
            t.call("x")
        except ProviderDown:
            t.breaker.record_failure(now=float(i))
    assert not t.breaker.closed(now=3.0), "breaker should be open"
    assert t.breaker.closed(now=40.0), "breaker should half-open after cooldown"

    print("Degradation ladder + circuit breaker: OK")
    print(f"  served tier={r['tier']} degraded={r['degraded']}, "
          f"events {len(ladder.events)}")

The FedRAMP Moderate control, as code

NIST 800-53 control map with a boundary-crossing check. This is the artifact an assessor asks for under FedRAMP Moderate specifically — it is not the same control as the one above, and a system that implements one does not thereby implement the other. It executes under the same publish gate.

"""NIST 800-53 control satisfaction map with an authorisation-boundary check.

FedRAMP reviewers do not ask whether the system is secure. They ask which
control, by identifier, each component satisfies, and what crosses the
authorisation boundary. An external model endpoint is a boundary crossing, and
an undeclared crossing is the finding that stalls an ATO.
"""

MODERATE_BASELINE = {
    "AC-4": "Information flow enforcement",
    "AU-2": "Event logging",
    "AU-9": "Protection of audit information",
    "CA-3": "Information exchange / external connections",
    "SC-7": "Boundary protection",
    "SC-8": "Transmission confidentiality and integrity",
    "SC-28": "Protection of information at rest",
    "SI-4": "System monitoring",
}


class AuthorisationBoundary:
    def __init__(self, name: str):
        self.name = name
        self.components: dict[str, dict] = {}
        self.crossings: list[dict] = []

    def declare(self, component: str, inside: bool, controls: list[str]) -> None:
        unknown = [c for c in controls if c not in MODERATE_BASELINE]
        if unknown:
            raise KeyError(f"not in the Moderate baseline: {unknown}")
        self.components[component] = {"inside": inside, "controls": set(controls)}

    def connect(self, src: str, dst: str, declared: bool) -> None:
        for end in (src, dst):
            if end not in self.components:
                raise KeyError(f"undeclared component: {end}")
        crossing = self.components[src]["inside"] != self.components[dst]["inside"]
        self.crossings.append({"src": src, "dst": dst,
                               "boundary_crossing": crossing, "declared": declared})

    def undeclared_crossings(self) -> list[dict]:
        return [c for c in self.crossings if c["boundary_crossing"] and not c["declared"]]

    def coverage(self) -> dict:
        covered = set()
        for meta in self.components.values():
            covered |= meta["controls"]
        gaps = sorted(set(MODERATE_BASELINE) - covered)
        return {"covered": sorted(covered), "gaps": gaps,
                "ato_ready": not gaps and not self.undeclared_crossings()}


if __name__ == "__main__":
    b = AuthorisationBoundary("agency-llm-enclave")
    b.declare("gateway", True, ["AC-4", "SC-7", "SC-8"])
    b.declare("audit_store", True, ["AU-2", "AU-9", "SC-28"])
    b.declare("monitor", True, ["SI-4"])
    b.declare("external_model_api", False, ["CA-3"])

    b.connect("gateway", "audit_store", declared=True)
    b.connect("gateway", "external_model_api", declared=True)
    cov = b.coverage()
    assert cov["ato_ready"], cov
    assert cov["gaps"] == [], cov

    # The finding this exists to catch: a crossing nobody declared.
    b2 = AuthorisationBoundary("agency-llm-enclave")
    b2.declare("gateway", True, list(MODERATE_BASELINE))
    b2.declare("telemetry_sidecar", False, ["CA-3"])
    b2.connect("gateway", "telemetry_sidecar", declared=False)
    assert not b2.coverage()["ato_ready"], b2.coverage()
    assert len(b2.undeclared_crossings()) == 1, b2.undeclared_crossings()

    try:
        b2.declare("rogue", True, ["XX-1"])
        raise AssertionError("accepted a control outside the baseline")
    except KeyError:
        pass

    print("FedRAMP Moderate boundary + control map: OK")
    print(f"  controls covered {len(cov['covered'])}/{len(MODERATE_BASELINE)}, "
          f"undeclared crossings {len(b2.undeclared_crossings())}")

Reference architecture

Labelled Degradation Ladder — the request path, with the decision points that must exist before the first model call:

flowchart LR
    REQ[Request + min_quality] --> T1{Tier 1 breaker closed?}
    T1 -->|open| T2{Tier 2}
    T1 -->|closed| CALL1[Call tier 1]
    CALL1 -->|fails| BRK[Record failure<br/>maybe open breaker] --> T2
    T2 -->|below min_quality| REFUSE[Refuse: no acceptable tier]
    T2 -->|ok| CALL2[Call tier 2] --> LAB[Label response<br/>degraded=true]

Implementation components

1. Quality-ranked tiers — Explicit integer quality per provider, not an implicit order.
2. Circuit breaker — A failing tier leaves rotation instead of being retried into the ground.
3. Half-open probe — One probe after cooldown; recovery is tested, not assumed.
4. Tier label on response — Every answer names its tier and whether it was degraded.
5. Quality floor per caller — A caller declares a minimum; below it is a refusal.
6. Degradation events — Each failover recorded — the signal the incident needs.

Controls and acceptance parameters

Each row carries an acceptance parameter rather than an adjective, because "low latency" cannot be signed off. Retention here is bound by per the data class retention schedule, enforced automatically.

What the auditor will ask

• Which NIST 800-53 control does each component satisfy, and which components sit outside the authorisation boundary?
  Each component carries its control identifiers in configuration, and the boundary diagram is generated from that configuration so it cannot drift from reality.
• When the primary provider fails, how does a downstream consumer learn the answer came from a weaker model?
  The response names the tier that produced it and carries a degraded flag. A consumer reading the label can treat a degraded answer differently; silent failover is what this design exists to prevent.
• What stops a failing provider from being retried thousands of times a minute?
  The circuit breaker. After the failure threshold it opens and the tier is skipped entirely until the cooldown elapses, so a failing provider leaves rotation rather than absorbing retries.
• Can a caller that requires top-tier quality be served a degraded answer?
  No. The caller declares a minimum quality and tiers below it are never attempted — the ladder raises instead of serving, which is the correct outcome when no acceptable tier exists.
• How do you know a recovered provider is actually healthy before restoring full traffic?
  The breaker goes half-open after cooldown and admits a single probe. Full rotation is restored only after that probe succeeds, so recovery is tested rather than assumed.
• What prevents failover from moving data outside the contracted region?
  Each tier carries a residency attribute and policy excludes out-of-region tiers from the ladder, so a failover cannot quietly relocate processing.

Related architectures

• Part of enterprise ai compliance architecture.
• The same control appears in HIPAA provider failover and degradation architecture for enterprise LLM.
• A different failure mode of the same component: EU AI Act provider failover and degradation architecture for enterprise.
• A different failure mode of the same component: GDPR provider failover and degradation architecture for enterprise LLM.
• For the related constraint, see SOX provider failover and degradation architecture for enterprise LLM.
• If this is the blocker in front of you: enterprise AI infrastructure review.