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+# S3 Rate Limiting
+
+SeaweedFS provides rate limiting features to control resource usage and prevent overload on the S3 API server. There are two mechanisms available:
+
+1. **Concurrent Upload Limiting** - Command-line flags for simple upload throttling
+2. **Circuit Breaker** - Advanced per-action and per-bucket rate limiting
+
+## Concurrent Upload Limiting
+
+These command-line flags control the total concurrent upload capacity when starting `weed s3`:
+
+| Flag | Default | Description |
+|------|---------|-------------|
+| `-concurrentUploadLimitMB` | 128 | Limit total concurrent upload data size in MB |
+| `-concurrentFileUploadLimit` | 0 | Limit number of concurrent file uploads (0 = unlimited) |
+
+### Example
+
+```bash
+# Limit concurrent uploads to 256MB total data and max 100 files
+weed s3 -filer=localhost:8888 -concurrentUploadLimitMB=256 -concurrentFileUploadLimit=100
+```
+
+### Behavior
+
+- These limits apply to **write operations** (PUT/POST)
+- When limits are exceeded, new requests **wait** until capacity is available (backpressure)
+- Requests are not rejected; they queue until the in-flight data/count drops below the limit
+- Metrics are exposed via Prometheus: `seaweedfs_s3_inflight_upload_count` and `seaweedfs_s3_inflight_upload_bytes`
+
+## Circuit Breaker
+
+The circuit breaker provides more granular rate limiting that can be configured globally or per-bucket, and by action type.
+
+### Configuration
+
+Circuit breaker is configured via `weed shell` and stored in the filer at `/etc/s3/circuit_breaker.json`. Changes are picked up dynamically by the S3 server.
+
+### Available Actions
+
+| Action | Description |
+|--------|-------------|
+| `Read` | GET/HEAD object operations |
+| `Write` | PUT/POST object operations |
+| `List` | List bucket/objects operations |
+| `Tagging` | Object tagging operations |
+| `Admin` | Administrative operations |
+
+### Limit Types
+
+| Type | Description |
+|------|-------------|
+| `count` | Maximum number of simultaneous requests |
+| `MB` | Maximum total content size (in MB) of simultaneous requests |
+
+### Examples
+
+#### Global Limits
+
+```bash
+# Limit globally: max 500 concurrent Read requests, max 200 concurrent Write requests
+weed shell
+> s3.circuitBreaker -global -type count -actions Read,Write -values 500,200 -apply
+
+# Limit by content size: max 1024MB concurrent Write data globally
+> s3.circuitBreaker -global -type MB -actions Write -values 1024 -apply
+
+# Apply same limit to all actions
+> s3.circuitBreaker -global -type count -actions Read,Write,List,Tagging,Admin -values 100 -apply
+```
+
+#### Per-Bucket Limits
+
+```bash
+# Limit specific buckets: max 200 concurrent Reads, 100 concurrent Writes
+> s3.circuitBreaker -buckets mybucket,otherbucket -type count -actions Read,Write -values 200,100 -apply
+
+# Different limits per action for a bucket
+> s3.circuitBreaker -buckets critical-bucket -type count -actions Read -values 50 -apply
+> s3.circuitBreaker -buckets critical-bucket -type count -actions Write -values 10 -apply
+```
+
+#### Managing Configuration
+
+```bash
+# View current configuration (without -apply)
+> s3.circuitBreaker
+
+# Disable circuit breaker for specific buckets
+> s3.circuitBreaker -buckets mybucket -disable -apply
+
+# Disable global circuit breaker
+> s3.circuitBreaker -global -disable -apply
+
+# Delete circuit breaker config for specific buckets
+> s3.circuitBreaker -buckets mybucket -delete -apply
+
+# Delete specific actions from global config
+> s3.circuitBreaker -global -actions Read -type count -delete -apply
+
+# Clear all circuit breaker configuration
+> s3.circuitBreaker -delete -apply
+```
+
+### Behavior
+
+- When limits are exceeded, the server returns **HTTP 429 (Too Many Requests)** with error code `SlowDown`
+- When byte limits are exceeded, returns error code `RequestBytesExceed`
+- Both global and bucket-specific limits are checked; the request must pass both
+- Configuration changes are applied dynamically without restarting the S3 server
+
+### Configuration File Format
+
+The circuit breaker configuration is stored as JSON. Here's an example of what the configuration looks like:
+
+```json
+{
+  "global": {
+    "enabled": true,
+    "actions": {
+      "Read:count": 500,
+      "Write:count": 200,
+      "Write:bytes": 1073741824
+    }
+  },
+  "buckets": {
+    "mybucket": {
+      "enabled": true,
+      "actions": {
+        "Read:count": 100,
+        "Write:count": 50
+      }
+    }
+  }
+}
+```
+
+## Choosing the Right Approach
+
+| Use Case | Recommended Approach |
+|----------|---------------------|
+| Simple upload throttling | `-concurrentUploadLimitMB` and `-concurrentFileUploadLimit` flags |
+| Per-bucket limits | Circuit breaker with `-buckets` |
+| Different limits per action type | Circuit breaker with `-actions` |
+| Dynamic configuration changes | Circuit breaker (no restart needed) |
+| Reject requests when overloaded | Circuit breaker (returns 429) |
+| Queue requests when overloaded | Concurrent upload flags (backpressure) |
+
+## Monitoring
+
+Rate limiting metrics are exposed via Prometheus when `-metricsPort` is configured:
+
+```bash
+weed s3 -filer=localhost:8888 -metricsPort=9327
+```
+
+Relevant metrics:
+- `seaweedfs_s3_inflight_upload_count` - Current number of in-flight uploads
+- `seaweedfs_s3_inflight_upload_bytes` - Current bytes of in-flight upload data
+- `seaweedfs_s3_request_total` - Total requests by action and status (look for 429 status)
+
diff --git a/_Sidebar.md b/_Sidebar.md
index 744e14e..2f02b58 100644
--- a/_Sidebar.md
+++ b/_Sidebar.md
@@ -82,6 +82,7 @@
 * [[S3 API Benchmark]]
 * [[S3 API FAQ]]
 * [[S3 Bucket Quota]]
+* [[S3 Rate Limiting]]
 * [[S3 API Audit log]]
 * [[S3 Nginx Proxy]]
 * [[Docker Compose for S3]]