Merge current v2.3 branch into master

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                        |