feat: add in flight connection middleware

docs/content/middlewares/tcp/inflightconn.md

@@ -0,0 +1,63 @@
+# InFlightConn
+
+Limiting the Number of Simultaneous connections.
+{: .subtitle }
+
+To proactively prevent services from being overwhelmed with high load, the number of allowed simultaneous connections by IP can be limited.
+
+## Configuration Examples
+
+```yaml tab="Docker"
+labels:
+  - "traefik.tcp.middlewares.test-inflightconn.inflightconn.amount=10"
+```
+
+```yaml tab="Kubernetes"
+apiVersion: traefik.containo.us/v1alpha1
+kind: Middleware
+metadata:
+  name: test-inflightconn
+spec:
+  inFlightConn:
+    amount: 10
+```
+
+```yaml tab="Consul Catalog"
+# Limiting to 10 simultaneous connections
+- "traefik.tcp.middlewares.test-inflightconn.inflightconn.amount=10"
+```
+
+```json tab="Marathon"
+"labels": {
+  "traefik.tcp.middlewares.test-inflightconn.inflightconn.amount": "10"
+}
+```
+
+```yaml tab="Rancher"
+# Limiting to 10 simultaneous connections.
+labels:
+  - "traefik.tcp.middlewares.test-inflightconn.inflightconn.amount=10"
+```
+
+```yaml tab="File (YAML)"
+# Limiting to 10 simultaneous connections.
+tcp:
+  middlewares:
+    test-inflightconn:
+      inFlightConn:
+        amount: 10
+```
+
+```toml tab="File (TOML)"
+# Limiting to 10 simultaneous connections
+[tcp.middlewares]
+  [tcp.middlewares.test-inflightconn.inFlightConn]
+    amount = 10
+```
+
+## Configuration Options
+
+### `amount`
+
+The `amount` option defines the maximum amount of allowed simultaneous connections.
+The middleware closes the connection if there are already `amount` connections opened.

docs/content/middlewares/tcp/overview.md

@@ -131,4 +131,5 @@ tcp:
 
 | Middleware                                | Purpose                                           | Area                        |
 |-------------------------------------------|---------------------------------------------------|-----------------------------|
-| [IPWhiteList](ipwhitelist.md)             | Limit the allowed client IPs                      | Security, Request lifecycle |
+| [InFlightConn](inflightconn.md)           | Limits the number of simultaneous connections.    | Security, Request lifecycle |
+| [IPWhiteList](ipwhitelist.md)             | Limit the allowed client IPs.                     | Security, Request lifecycle |

docs/content/reference/dynamic-configuration/traefik.containo.us_middlewaretcps.yaml

@@ -36,6 +36,13 @@ spec:
           spec:
             description: MiddlewareTCPSpec holds the MiddlewareTCP configuration.
             properties:
+              inFlightConn:
+                description: TCPInFlightConn holds the TCP in flight connection configuration.
+                properties:
+                  amount:
+                    format: int64
+                    type: integer
+                type: object
               ipWhiteList:
                 description: TCPIPWhiteList holds the TCP ip white list configuration.
                 properties: