Moving Provider Namespace documentation topic to Configuration Discovery section

docs/content/middlewares/overview.md

@@ -11,6 +11,11 @@ There are several available middleware in Traefik, some can modify the request,
 
 Pieces of middleware can be combined in chains to fit every scenario.
 
+!!! warning "Provider Namespace"
+
+    Be aware of the concept of Providers Namespace described in the [Configuration Discovery](../providers/overview.md#provider-namespace) section. 
+    It also applies to Middlewares.
+
 ## Configuration Example
 
 ```yaml tab="Docker"
@@ -128,106 +133,6 @@ http:
           - url: "http://127.0.0.1:80"
 ```
 
-## Provider Namespace
-
-When you declare a middleware, it lives in its provider's namespace.
-For example, if you declare a middleware using a Docker label, under the hoods, it will reside in the docker provider namespace.
-
-If you use multiple providers and wish to reference a middleware declared in another provider
-(aka referencing a cross-provider middleware),
-then you'll have to append to the middleware name, the `@` separator, followed by the provider name.
-
-```text
-<resource-name>@<provider-name>
-```
-
-!!! important "Kubernetes Namespace"
-
-    As Kubernetes also has its own notion of namespace, one should not confuse the "provider namespace"
-    with the "kubernetes namespace" of a resource when in the context of a cross-provider usage.
-    In this case, since the definition of the middleware is not in kubernetes,
-    specifying a "kubernetes namespace" when referring to the resource does not make any sense,
-    and therefore this specification would be ignored even if present.
-    On the other hand, if you declare the middleware as a Custom Resource in Kubernetes and use the 
-    non-crd Ingress objects, you'll have to add the kubernetes namespace of the middleware to the 
-    annotation like this `<middleware-namespace>-<middleware-name>@kubernetescrd`.
-
-!!! abstract "Referencing a Middleware from Another Provider"
-
-    Declaring the add-foo-prefix in the file provider.
-
-    ```toml tab="File (TOML)"
-    [http.middlewares]
-      [http.middlewares.add-foo-prefix.addPrefix]
-        prefix = "/foo"
-    ```
-    
-    ```yaml tab="File (YAML)"
-    http:
-      middlewares:
-        add-foo-prefix:
-          addPrefix:
-            prefix: "/foo"
-    ```
-
-    Using the add-foo-prefix middleware from other providers:
-
-    ```yaml tab="Docker"
-    your-container: #
-      image: your-docker-image
-
-      labels:
-        # Attach add-foo-prefix@file middleware (declared in file)
-        - "traefik.http.routers.my-container.middlewares=add-foo-prefix@file"
-    ```
-
-    ```yaml tab="Kubernetes Ingress Route"
-    apiVersion: traefik.containo.us/v1alpha1
-    kind: IngressRoute
-    metadata:
-      name: ingressroutestripprefix
-
-    spec:
-      entryPoints:
-        - web
-      routes:
-        - match: Host(`example.com`)
-          kind: Rule
-          services:
-            - name: whoami
-              port: 80
-          middlewares:
-            - name: add-foo-prefix@file
-            # namespace: bar
-            # A namespace specification such as above is ignored
-            # when the cross-provider syntax is used.
-    ```
-    
-    ```yaml tab="Kubernetes Ingress"
-    apiVersion: traefik.containo.us/v1alpha1
-    kind: Middleware
-    metadata:
-      name: stripprefix
-      namespace: appspace
-    spec:
-      stripPrefix:
-        prefixes:
-          - /stripit
-    
-    ---
-    apiVersion: networking.k8s.io/v1
-    kind: Ingress
-    metadata:
-      name: ingress
-      namespace: appspace
-      annotations:
-        # referencing a middleware from Kubernetes CRD provider: 
-        # <middleware-namespace>-<middleware-name>@kubernetescrd
-        "traefik.ingress.kubernetes.io/router.middlewares": appspace-stripprefix@kubernetescrd
-    spec:
-      # ... regular ingress definition
-    ```
-
 ## Available Middlewares
 
 | Middleware                                | Purpose                                           | Area                        |

docs/content/providers/overview.md

@@ -22,6 +22,106 @@ Even if each provider is different, we can categorize them in four groups:
 - Annotation based (a separate object, with annotations, defines the characteristics of the container)
 - File based (the good old configuration file)
 
+## Provider Namespace
+
+When you declare certain objects, in Traefik dynamic configuration,
+such as middleware, service, TLS options or servers transport, they live in its provider's namespace.
+For example, if you declare a middleware using a Docker label, under the hoods, it will reside in the docker provider namespace.
+
+If you use multiple providers and wish to reference such an object declared in another provider 
+(aka referencing a cross-provider object, e.g. middleware), then you'll have to append the `@` separator, 
+followed by the provider name to the object name.
+
+```text
+<resource-name>@<provider-name>
+```
+
+!!! important "Kubernetes Namespace"
+
+    As Kubernetes also has its own notion of namespace,
+    one should not confuse the "provider namespace" with the "kubernetes namespace" of a resource when in the context of a cross-provider usage.  
+    In this case, since the definition of a traefik dynamic configuration object is not in kubernetes,
+    specifying a "kubernetes namespace" when referring to the resource does not make any sense,
+    and therefore this specification would be ignored even if present.  
+    On the other hand, if you, say, declare a middleware as a Custom Resource in Kubernetes and use the non-crd Ingress objects,
+    you'll have to add the Kubernetes namespace of the middleware to the annotation like this `<middleware-namespace>-<middleware-name>@kubernetescrd`.
+
+!!! abstract "Referencing a Traedik dynamic configuration object from Another Provider"
+
+    Declaring the add-foo-prefix in the file provider.
+
+    ```toml tab="File (TOML)"
+    [http.middlewares]
+      [http.middlewares.add-foo-prefix.addPrefix]
+        prefix = "/foo"
+    ```
+    
+    ```yaml tab="File (YAML)"
+    http:
+      middlewares:
+        add-foo-prefix:
+          addPrefix:
+            prefix: "/foo"
+    ```
+
+    Using the add-foo-prefix middleware from other providers:
+
+    ```yaml tab="Docker"
+    your-container: #
+      image: your-docker-image
+
+      labels:
+        # Attach add-foo-prefix@file middleware (declared in file)
+        - "traefik.http.routers.my-container.middlewares=add-foo-prefix@file"
+    ```
+
+    ```yaml tab="Kubernetes Ingress Route"
+    apiVersion: traefik.containo.us/v1alpha1
+    kind: IngressRoute
+    metadata:
+      name: ingressroutestripprefix
+
+    spec:
+      entryPoints:
+        - web
+      routes:
+        - match: Host(`example.com`)
+          kind: Rule
+          services:
+            - name: whoami
+              port: 80
+          middlewares:
+            - name: add-foo-prefix@file
+            # namespace: bar
+            # A namespace specification such as above is ignored
+            # when the cross-provider syntax is used.
+    ```
+    
+    ```yaml tab="Kubernetes Ingress"
+    apiVersion: traefik.containo.us/v1alpha1
+    kind: Middleware
+    metadata:
+      name: stripprefix
+      namespace: appspace
+    spec:
+      stripPrefix:
+        prefixes:
+          - /stripit
+    
+    ---
+    apiVersion: networking.k8s.io/v1
+    kind: Ingress
+    metadata:
+      name: ingress
+      namespace: appspace
+      annotations:
+        # referencing a middleware from Kubernetes CRD provider: 
+        # <middleware-namespace>-<middleware-name>@kubernetescrd
+        "traefik.ingress.kubernetes.io/router.middlewares": appspace-stripprefix@kubernetescrd
+    spec:
+      # ... regular ingress definition
+    ```
+
 ## Supported Providers 
 
 Below is the list of the currently supported providers in Traefik.