Multi-layer routing

Co-authored-by: Romain <rtribotte@users.noreply.github.com>

pkg/config/dynamic/http_config.go

@@ -69,6 +69,7 @@ type Router struct {
 	Middlewares []string `json:"middlewares,omitempty" toml:"middlewares,omitempty" yaml:"middlewares,omitempty" export:"true"`
 	Service     string   `json:"service,omitempty" toml:"service,omitempty" yaml:"service,omitempty" export:"true"`
 	Rule        string   `json:"rule,omitempty" toml:"rule,omitempty" yaml:"rule,omitempty"`
+	ParentRefs  []string `json:"parentRefs,omitempty" toml:"parentRefs,omitempty" yaml:"parentRefs,omitempty" label:"-" export:"true"`
 	// Deprecated: Please do not use this field and rewrite the router rules to use the v3 syntax.
 	RuleSyntax    string                     `json:"ruleSyntax,omitempty" toml:"ruleSyntax,omitempty" yaml:"ruleSyntax,omitempty" export:"true"`
 	Priority      int                        `json:"priority,omitempty" toml:"priority,omitempty,omitzero" yaml:"priority,omitempty" export:"true"`

pkg/config/dynamic/zz_generated.deepcopy.go

@@ -1369,6 +1369,11 @@ func (in *Router) DeepCopyInto(out *Router) {
 		*out = make([]string, len(*in))
 		copy(*out, *in)
 	}
+	if in.ParentRefs != nil {
+		in, out := &in.ParentRefs, &out.ParentRefs
+		*out = make([]string, len(*in))
+		copy(*out, *in)
+	}
 	if in.TLS != nil {
 		in, out := &in.TLS, &out.TLS
 		*out = new(RouterTLSConfig)

pkg/config/runtime/runtime_http.go

@@ -43,7 +43,8 @@ func (c *Configuration) GetRoutersByEntryPoints(ctx context.Context, entryPoints
 			entryPointsRouters[entryPointName][rtName] = rt
 		}
 
-		if entryPointsCount == 0 {
+		// Root routers must have at least one entry point.
+		if entryPointsCount == 0 && rt.ParentRefs == nil {
 			rt.AddError(errors.New("no valid entryPoint for this router"), true)
 			logger.Error().Msg("No valid entryPoint for this router")
 		}
@@ -80,6 +81,11 @@ type RouterInfo struct {
 	// It is the caller's responsibility to set the initial status.
 	Status string   `json:"status,omitempty"`
 	Using  []string `json:"using,omitempty"` // Effective entry points used by that router.
+
+	// ChildRefs contains the names of child routers.
+	// This field is only filled during multi-layer routing computation of parentRefs,
+	// and used when building the runtime configuration.
+	ChildRefs []string `json:"-"`
 }
 
 // AddError adds err to r.Err, if it does not already exist.