Add documentation for ECS constraints option

docs/content/providers/ecs.md

@@ -137,6 +137,70 @@ providers:
 # ...
 ```
 
+### `constraints`
+
+_Optional, Default=""_
+
+The `constraints` option can be set to an expression that Traefik matches against the container labels (task),
+to determine whether to create any route for that container. 
+If none of the container labels match the expression, no route for that container is created. 
+If the expression is empty, all detected containers are included.
+
+The expression syntax is based on the `Label("key", "value")`, and `LabelRegex("key", "value")` functions,
+as well as the usual boolean logic, as shown in examples below.
+
+??? example "Constraints Expression Examples"
+
+    ```toml
+    # Includes only containers having a label with key `a.label.name` and value `foo`
+    constraints = "Label(`a.label.name`, `foo`)"
+    ```
+
+    ```toml
+    # Excludes containers having any label with key `a.label.name` and value `foo`
+    constraints = "!Label(`a.label.name`, `value`)"
+    ```
+
+    ```toml
+    # With logical AND.
+    constraints = "Label(`a.label.name`, `valueA`) && Label(`another.label.name`, `valueB`)"
+    ```
+
+    ```toml
+    # With logical OR.
+    constraints = "Label(`a.label.name`, `valueA`) || Label(`another.label.name`, `valueB`)"
+    ```
+
+    ```toml
+    # With logical AND and OR, with precedence set by parentheses.
+    constraints = "Label(`a.label.name`, `valueA`) && (Label(`another.label.name`, `valueB`) || Label(`yet.another.label.name`, `valueC`))"
+    ```
+
+    ```toml
+    # Includes only containers having a label with key `a.label.name` and a value matching the `a.+` regular expression.
+    constraints = "LabelRegex(`a.label.name`, `a.+`)"
+    ```
+
+For additional information, refer to [Restrict the Scope of Service Discovery](./overview.md#restrict-the-scope-of-service-discovery).
+
+```yaml tab="File (YAML)"
+providers:
+  ecs:
+    constraints: "Label(`a.label.name`,`foo`)"
+    # ...
+```
+
+```toml tab="File (TOML)"
+[providers.ecs]
+  constraints = "Label(`a.label.name`,`foo`)"
+  # ...
+```
+
+```bash tab="CLI"
+--providers.ecs.constraints=Label(`a.label.name`,`foo`)
+# ...
+```
+
 ### `defaultRule`
 
 _Optional, Default=```Host(`{{ normalize .Name }}`)```_

docs/content/providers/overview.md

@@ -213,6 +213,7 @@ you can do so in two different ways:
 List of providers that support these features:
 
 - [Docker](./docker.md#exposedbydefault)
+- [ECS](./ecs.md#exposedbydefault)
 - [Consul Catalog](./consul-catalog.md#exposedbydefault)
 - [Nomad](./nomad.md#exposedbydefault)
 - [Rancher](./rancher.md#exposedbydefault)
@@ -223,6 +224,7 @@ List of providers that support these features:
 List of providers that support constraints:
 
 - [Docker](./docker.md#constraints)
+- [ECS](./ecs.md#constraints)
 - [Consul Catalog](./consul-catalog.md#constraints)
 - [Nomad](./nomad.md#constraints)
 - [Rancher](./rancher.md#constraints)