Add Throttling to LISA Serve

lib/api-base/fastApiContainer.ts

@@ -111,7 +111,12 @@ export class FastApiContainer extends Construct {
             USER_GROUP: config.authConfig!.userGroup,
             RAG_ADMIN_GROUP: config.authConfig!.ragAdminGroup,
             JWT_GROUPS_PROP: config.authConfig!.jwtGroupsProperty,
-            MANAGEMENT_KEY_NAME: managementKeyName
+            MANAGEMENT_KEY_NAME: managementKeyName,
+            // Per-user rate limiting (in-process token bucket)
+            RATE_LIMIT_RPM: (config.restApiConfig.rateLimitRpm ?? 60).toString(),
+            RATE_LIMIT_BURST: (config.restApiConfig.rateLimitBurst ?? 10).toString(),
+            RATE_LIMIT_ENABLED: (config.restApiConfig.rateLimitEnabled ?? true).toString(),
+            RATE_LIMIT_OVERRIDES: JSON.stringify(config.restApiConfig.rateLimitOverrides ?? {}),
         };
 
         if (tokenTable) {

lib/schema/configSchema.ts

@@ -746,6 +746,25 @@ const FastApiContainerConfigSchema = z.object({
                     'APIs. Please do not define the dbHost field for the FastAPI container DB config.',
             },
         ),
+    rateLimitRpm: z.number().int().positive().default(60).describe(
+        'Per-user sustained request rate limit in requests per minute. Each ECS task enforces this independently.'
+    ),
+    rateLimitBurst: z.number().int().nonnegative().default(10).describe(
+        'Per-user burst allowance above the sustained rate limit. Allows short spikes without throttling.'
+    ),
+    rateLimitEnabled: z.boolean().default(true).describe(
+        'Enable or disable per-user rate limiting on the serve API.'
+    ),
+    rateLimitOverrides: z.record(
+        z.string(),
+        z.object({
+            rpm: z.number().int().positive().optional().describe('Override RPM for this user/token.'),
+            burst: z.number().int().nonnegative().optional().describe('Override burst for this user/token.'),
+        })
+    ).default({}).describe(
+        'Per-user rate limit overrides. Keys use the format "token:<tokenUUID>" for API tokens, ' +
+        '"oidc:<sub>" for OIDC users, or "user:<username>". Values can override "rpm" and/or "burst".'
+    ),
 }).describe('Configuration schema for REST API.');
 
 /** Custom domain / TLS for the MCP Workbench ALB only (separate from Serve’s `restApiConfig`). */

lib/serve/rest-api/src/main.py

@@ -24,6 +24,7 @@
 from middleware import (
     auth_middleware,
     process_request_middleware,
+    rate_limit_middleware,
     register_exception_handlers,
     security_middleware,
     validate_input_middleware,
@@ -82,12 +83,23 @@ async def lifespan(app: FastAPI):  # type: ignore
 ##############
 
 
+@app.middleware("http")
+async def rate_limit(request, call_next):  # type: ignore
+    """Per-user rate limiting middleware.
+
+    Runs after authentication (user identity is available) to enforce
+    per-API-key / per-user request rate limits.
+    """
+    return await rate_limit_middleware(request, call_next)
+
+
 @app.middleware("http")
 async def authenticate(request, call_next):  # type: ignore
     """Authentication middleware.
 
     Validates tokens and sets user context on request.state.
-    Runs after security checks but before request processing.
+    NOTE: Function middleware executes in reverse registration order in FastAPI,
+    so this must be declared *after* rate_limit() to run first on requests.
     """
     return await auth_middleware(request, call_next)
 

lib/serve/rest-api/src/middleware/__init__.py

@@ -16,12 +16,14 @@
 from .auth_middleware import auth_middleware, require_admin, require_auth
 from .exception_handlers import register_exception_handlers
 from .input_validation import validate_input_middleware
+from .rate_limit_middleware import rate_limit_middleware
 from .request_middleware import process_request_middleware
 from .security_middleware import security_middleware
 
 __all__ = [
     "auth_middleware",
     "process_request_middleware",
+    "rate_limit_middleware",
     "register_exception_handlers",
     "require_admin",
     "require_auth",

lib/serve/rest-api/src/middleware/rate_limit_middleware.py

@@ -0,0 +1,267 @@
+#   Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+#
+#   Licensed under the Apache License, Version 2.0 (the "License").
+#   You may not use this file except in compliance with the License.
+#   You may obtain a copy of the License at
+#
+#       http://www.apache.org/licenses/LICENSE-2.0
+#
+#   Unless required by applicable law or agreed to in writing, software
+#   distributed under the License is distributed on an "AS IS" BASIS,
+#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#   See the License for the specific language governing permissions and
+#   limitations under the License.
+
+"""Per-user rate limiting middleware using an in-memory token bucket.
+
+Runs after authentication so the caller identity is available on ``request.state``.
+Each ECS task tracks limits independently — the effective per-user limit across the
+fleet is ``N_tasks × RATE_LIMIT_RPM``, which naturally scales with capacity.
+
+Configuration (environment variables):
+    RATE_LIMIT_RPM   – sustained requests per minute per user (default 60)
+    RATE_LIMIT_BURST – extra burst allowance above the sustained rate (default 10)
+    RATE_LIMIT_ENABLED – set to "false" to disable (default "true")
+    RATE_LIMIT_OVERRIDES – JSON map of per-user/per-token overrides (default "{}")
+        Keys match the user_key format: "token:<tokenUUID>" or "oidc:<sub>" or "user:<username>"
+        Values are objects with optional "rpm" and "burst" fields.
+        Example: {"token:abc-123": {"rpm": 120, "burst": 20}, "oidc:user-456": {"rpm": 10}}
+"""
+
+import json
+import os
+import threading
+import time
+from collections.abc import Callable
+
+from fastapi import Request, Response
+from fastapi.responses import JSONResponse
+from loguru import logger
+from starlette.status import HTTP_429_TOO_MANY_REQUESTS
+
+# ---------------------------------------------------------------------------
+# Configuration
+# ---------------------------------------------------------------------------
+RATE_LIMIT_RPM = int(os.environ.get("RATE_LIMIT_RPM", "60"))
+RATE_LIMIT_BURST = int(os.environ.get("RATE_LIMIT_BURST", "10"))
+RATE_LIMIT_ENABLED = os.environ.get("RATE_LIMIT_ENABLED", "true").lower() == "true"
+
+
+# Per-user overrides: { "token:<uuid>": {"rpm": N, "burst": N}, ... }
+def _parse_overrides(raw: str) -> dict[str, dict[str, int]]:
+    """Parse the RATE_LIMIT_OVERRIDES JSON env var into a validated dict."""
+    if not raw:
+        return {}
+    try:
+        parsed = json.loads(raw)
+        if not isinstance(parsed, dict):
+            logger.warning("RATE_LIMIT_OVERRIDES is not a JSON object, ignoring")
+            return {}
+        result: dict[str, dict[str, int]] = {}
+        for key, val in parsed.items():
+            if not isinstance(val, dict):
+                logger.warning(f"RATE_LIMIT_OVERRIDES[{key}] is not an object, skipping")
+                continue
+            entry: dict[str, int] = {}
+            if "rpm" in val:
+                entry["rpm"] = int(val["rpm"])
+            if "burst" in val:
+                entry["burst"] = int(val["burst"])
+            result[str(key)] = entry
+        return result
+    except (json.JSONDecodeError, ValueError) as e:
+        logger.warning(f"Failed to parse RATE_LIMIT_OVERRIDES: {e}")
+        return {}
+
+
+RATE_LIMIT_OVERRIDES: dict[str, dict[str, int]] = _parse_overrides(os.environ.get("RATE_LIMIT_OVERRIDES", ""))
+
+# Derived: tokens added per second (system default)
+_REFILL_RATE = RATE_LIMIT_RPM / 60.0
+
+# Paths exempt from rate limiting
+_EXEMPT_PATHS = {"/health", "/health/readiness", "/health/liveliness"}
+
+# Maximum number of tracked users before we prune stale entries
+_MAX_BUCKETS = 10_000
+# Entries older than this (seconds) are eligible for pruning
+_STALE_SECONDS = 300.0
+
+
+# ---------------------------------------------------------------------------
+# Token bucket implementation
+# ---------------------------------------------------------------------------
+
+
+class _TokenBucket:
+    """Simple token bucket for a single user.
+
+    Not thread-safe on its own — callers must hold ``_lock``.
+    """
+
+    __slots__ = ("tokens", "last_refill")
+
+    def __init__(self, max_tokens: float) -> None:
+        self.tokens: float = max_tokens
+        self.last_refill: float = time.monotonic()
+
+    def try_consume(self, max_tokens: float, refill_rate: float) -> tuple[bool, float]:
+        """Refill and attempt to consume one token.
+
+        Returns ``(allowed, retry_after_seconds)``.
+        """
+        now = time.monotonic()
+        elapsed = now - self.last_refill
+        self.tokens = min(max_tokens, self.tokens + elapsed * refill_rate)
+        self.last_refill = now
+
+        if self.tokens >= 1.0:
+            self.tokens -= 1.0
+            return True, 0.0
+
+        # How long until one token is available
+        wait = (1.0 - self.tokens) / refill_rate
+        return False, wait
+
+
+# Global bucket store — keyed by user identity string
+_buckets: dict[str, _TokenBucket] = {}
+_lock = threading.Lock()
+
+
+def _get_max_tokens() -> float:
+    """Max tokens = sustained rate (per minute converted to bucket size) + burst.
+
+    Returns the system default. For per-user values use ``_get_user_limits``.
+    """
+    return float(RATE_LIMIT_RPM) + float(RATE_LIMIT_BURST)
+
+
+def _get_user_limits(user_key: str) -> tuple[float, float, float]:
+    """Return (max_tokens, refill_rate, rpm) for a specific user.
+
+    Checks ``RATE_LIMIT_OVERRIDES`` first, falls back to system defaults.
+    """
+    override = RATE_LIMIT_OVERRIDES.get(user_key)
+    if override:
+        rpm = override.get("rpm", RATE_LIMIT_RPM)
+        burst = override.get("burst", RATE_LIMIT_BURST)
+    else:
+        rpm = RATE_LIMIT_RPM
+        burst = RATE_LIMIT_BURST
+    max_tokens = float(rpm) + float(burst)
+    refill_rate = rpm / 60.0
+    return max_tokens, refill_rate, float(rpm)
+
+
+def _prune_stale_buckets() -> None:
+    """Remove buckets that haven't been touched recently. Must hold ``_lock``."""
+    now = time.monotonic()
+    stale_keys = [k for k, b in _buckets.items() if (now - b.last_refill) > _STALE_SECONDS]
+    for k in stale_keys:
+        del _buckets[k]
+
+
+def _check_rate_limit(user_key: str) -> tuple[bool, float]:
+    """Check whether *user_key* is within its rate limit.
+
+    Returns ``(allowed, retry_after_seconds)``.
+    Uses per-user overrides from ``RATE_LIMIT_OVERRIDES`` when available.
+    """
+    max_tokens, refill_rate, _ = _get_user_limits(user_key)
+
+    with _lock:
+        if len(_buckets) >= _MAX_BUCKETS:
+            _prune_stale_buckets()
+
+        bucket = _buckets.get(user_key)
+        if bucket is None:
+            bucket = _TokenBucket(max_tokens)
+            _buckets[user_key] = bucket
+
+        return bucket.try_consume(max_tokens, refill_rate)
+
+
+# ---------------------------------------------------------------------------
+# User identity extraction
+# ---------------------------------------------------------------------------
+
+
+def _get_user_key(request: Request) -> str | None:
+    """Derive a rate-limit key from the authenticated request.
+
+    Returns ``None`` for requests that should bypass rate limiting
+    (management tokens, unauthenticated/public paths).
+    """
+    # Management tokens bypass rate limiting — they're internal automation
+    if not hasattr(request.state, "authenticated"):
+        return None
+
+    # API token users — key on tokenUUID (unique per key)
+    if hasattr(request.state, "api_token_info"):
+        token_info = request.state.api_token_info
+        token_uuid = token_info.get("tokenUUID")
+        if token_uuid:
+            return f"token:{token_uuid}"
+        # Fallback to username if no UUID (shouldn't happen for valid tokens)
+        return f"token:{token_info.get('username', 'unknown')}"
+
+    # OIDC users — key on subject claim
+    jwt_data = getattr(request.state, "jwt_data", None)
+    if jwt_data and isinstance(jwt_data, dict):
+        sub = jwt_data.get("sub") or jwt_data.get("username")
+        if sub:
+            return f"oidc:{sub}"
+
+    # Fallback to username set by auth middleware
+    username = getattr(request.state, "username", None)
+    if username:
+        return f"user:{username}"
+
+    return None
+
+
+# ---------------------------------------------------------------------------
+# Middleware entry point
+# ---------------------------------------------------------------------------
+
+
+async def rate_limit_middleware(request: Request, call_next: Callable[[Request], Response]) -> Response:
+    """Per-user rate limiting middleware.
+
+    Must run **after** authentication middleware so that ``request.state``
+    contains the caller identity.
+    """
+    if not RATE_LIMIT_ENABLED:
+        return await call_next(request)
+
+    # Skip exempt paths
+    if request.url.path in _EXEMPT_PATHS:
+        return await call_next(request)
+
+    # Skip OPTIONS (CORS preflight)
+    if request.method == "OPTIONS":
+        return await call_next(request)
+
+    user_key = _get_user_key(request)
+    if user_key is None:
+        # Can't identify user or exempt category — let it through
+        return await call_next(request)
+
+    allowed, retry_after = _check_rate_limit(user_key)
+
+    if not allowed:
+        logger.warning(f"Rate limit exceeded for {user_key}, retry_after={retry_after:.1f}s")
+        return JSONResponse(
+            status_code=HTTP_429_TOO_MANY_REQUESTS,
+            content={
+                "error": {
+                    "message": "Rate limit exceeded. Please slow down and retry.",
+                    "type": "rate_limit_error",
+                    "code": "rate_limit_exceeded",
+                }
+            },
+            headers={"Retry-After": str(int(retry_after) + 1)},
+        )
+
+    return await call_next(request)