security: configurable rate limit fail policy via RATE_LIMIT_FAIL_POLICY

Add "deny" as alias for "closed" policy. Change fail-closed retry-after
from 1s to 60s to give Redis time to recover. Add from_env default test.
Document env var in CLAUDE.md.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -91,6 +91,7 @@ OPENAI_API_KEY=sk-... cargo run -p anyllm_proxy
 - `IP_ALLOWLIST`: Comma-separated CIDR ranges for IP allowlisting (e.g., `192.168.1.0/24,10.0.0.0/8`). Bare IPs also accepted. When set, only matching IPs can access the proxy.
 - `TRUST_PROXY_HEADERS`: Set to `true` or `1` to use `X-Forwarded-For` header for client IP when behind a reverse proxy. Only effective when `IP_ALLOWLIST` is set.
 - `WEBHOOK_URLS`: Comma-separated webhook URLs for request completion notifications. Fire-and-forget HTTP POST with `RequestLogEntry` JSON payload.
+- `RATE_LIMIT_FAIL_POLICY`: Behavior when Redis rate limiter is unavailable: `open` (default, allow requests) or `closed`/`deny` (reject with 503 and retry-after 60s).
 
 ### LiteLLM env var aliases
 

crates/proxy/src/ratelimit.rs

@@ -17,7 +17,7 @@ pub enum RateLimitFailPolicy {
 impl RateLimitFailPolicy {
     pub fn from_env_str(s: &str) -> Self {
         match s.to_lowercase().as_str() {
-            "closed" => Self::Closed,
+            "closed" | "deny" => Self::Closed,
             _ => Self::Open,
         }
     }
@@ -97,7 +97,7 @@ impl RedisRateLimiter {
                 }
                 RateLimitFailPolicy::Closed => {
                     tracing::error!(error = %e, "Redis RPM check failed, rejecting request (fail-closed)");
-                    Err(1)
+                    Err(60)
                 }
             },
         }
@@ -164,7 +164,7 @@ impl RedisRateLimiter {
                 }
                 RateLimitFailPolicy::Closed => {
                     tracing::error!(error = %e, "Redis TPM check failed, rejecting request (fail-closed)");
-                    Err(1)
+                    Err(60)
                 }
             },
         }
@@ -265,9 +265,25 @@ mod tests {
             RateLimitFailPolicy::from_env_str("CLOSED"),
             RateLimitFailPolicy::Closed
         ));
+        assert!(matches!(
+            RateLimitFailPolicy::from_env_str("deny"),
+            RateLimitFailPolicy::Closed
+        ));
+        assert!(matches!(
+            RateLimitFailPolicy::from_env_str("DENY"),
+            RateLimitFailPolicy::Closed
+        ));
         assert!(matches!(
             RateLimitFailPolicy::from_env_str("unknown"),
             RateLimitFailPolicy::Open
         ));
     }
+
+    #[test]
+    fn fail_policy_defaults_to_open() {
+        // When RATE_LIMIT_FAIL_POLICY is unset, from_env should return Open.
+        std::env::remove_var("RATE_LIMIT_FAIL_POLICY");
+        let policy = RateLimitFailPolicy::from_env();
+        assert_eq!(policy, RateLimitFailPolicy::Open);
+    }
 }