Add "fallback read" mode.

If `Origin.EnableFallbackRead` is set, then the origin will be selected by the director
to serve clients if there are no available caches.

Fixes #608

director/cache_ads.go

@@ -46,14 +46,15 @@ type (
 	}
 
 	ServerAd struct {
-		Name        string
-		AuthURL     url.URL
-		URL         url.URL // This is server's XRootD URL for file transfer
-		WebURL      url.URL // This is server's Web interface and API
-		Type        ServerType
-		Latitude    float64
-		Longitude   float64
-		EnableWrite bool
+		Name               string
+		AuthURL            url.URL
+		URL                url.URL // This is server's XRootD URL for file transfer
+		WebURL             url.URL // This is server's Web interface and API
+		Type               ServerType
+		Latitude           float64
+		Longitude          float64
+		EnableWrite        bool
+		EnableFallbackRead bool // True if reads from the origin are permitted when no cache is available
 	}
 
 	ServerType   string

director/origin_api.go

@@ -41,11 +41,12 @@ import (
 
 type (
 	OriginAdvertise struct {
-		Name        string        `json:"name"`
-		URL         string        `json:"url"`               // This is the url for origin's XRootD service and file transfer
-		WebURL      string        `json:"web_url,omitempty"` // This is the url for origin's web engine and APIs
-		Namespaces  []NamespaceAd `json:"namespaces"`
-		EnableWrite bool          `json:"enablewrite"`
+		Name               string        `json:"name"`
+		URL                string        `json:"url"`               // This is the url for origin's XRootD service and file transfer
+		WebURL             string        `json:"web_url,omitempty"` // This is the url for origin's web engine and APIs
+		Namespaces         []NamespaceAd `json:"namespaces"`
+		EnableWrite        bool          `json:"enablewrite"`
+		EnableFallbackRead bool          `json:"enable-fallback-read"` // True if the origin will allow direct client reads when no caches are available
 	}
 )
 

director/redirect.go

@@ -179,7 +179,7 @@ func RedirectToCache(ginCtx *gin.Context) {
 
 	authzBearerEscaped := getAuthzEscaped(ginCtx.Request)
 
-	namespaceAd, _, cacheAds := GetAdsForPath(reqPath)
+	namespaceAd, originAds, cacheAds := GetAdsForPath(reqPath)
 	// if GetAdsForPath doesn't find any ads because the prefix doesn't exist, we should
 	// report the lack of path first -- this is most important for the user because it tells them
 	// they're trying to get an object that simply doesn't exist
@@ -189,13 +189,22 @@ func RedirectToCache(ginCtx *gin.Context) {
 	}
 	// If the namespace prefix DOES exist, then it makes sense to say we couldn't find a valid cache.
 	if len(cacheAds) == 0 {
-		ginCtx.String(404, "No cache found for path\n")
-		return
-	}
-	cacheAds, err = SortServers(ipAddr, cacheAds)
-	if err != nil {
-		ginCtx.String(500, "Failed to determine server ordering")
-		return
+		for _, originAd := range originAds {
+			if originAd.EnableFallbackRead {
+				cacheAds = append(cacheAds, originAd)
+				break
+			}
+		}
+		if len(cacheAds) == 0 {
+			ginCtx.String(http.StatusNotFound, "No cache found for path")
+			return
+		}
+	} else {
+		cacheAds, err = SortServers(ipAddr, cacheAds)
+		if err != nil {
+			ginCtx.String(http.StatusInternalServerError, "Failed to determine server ordering")
+			return
+		}
 	}
 	redirectURL := getRedirectURL(reqPath, cacheAds[0], namespaceAd.RequireToken)
 
@@ -462,12 +471,13 @@ func registerServeAd(engineCtx context.Context, ctx *gin.Context, sType ServerTy
 	}
 
 	sAd := ServerAd{
-		Name:        ad.Name,
-		AuthURL:     *ad_url,
-		URL:         *ad_url,
-		WebURL:      *adWebUrl,
-		Type:        sType,
-		EnableWrite: ad.EnableWrite,
+		Name:               ad.Name,
+		AuthURL:            *ad_url,
+		URL:                *ad_url,
+		WebURL:             *adWebUrl,
+		Type:               sType,
+		EnableWrite:        ad.EnableWrite,
+		EnableFallbackRead: ad.EnableFallbackRead,
 	}
 
 	hasOriginAdInCache := serverAds.Has(sAd)

docs/parameters.yaml

@@ -309,6 +309,14 @@ type: bool
 default: true
 components: ["origin"]
 ---
+name: Origin.EnableFallbackRead
+description: >-
+  Set to `true` if the origin permits clients to directly read from it
+  when no cache service is available
+type: bool
+default: false
+components: ["origin"]
+---
 name: Origin.Multiuser
 description: >-
   A bool indicating whether an origin is "multiuser", ie whether the underlying XRootD instance must be configured in multi user mode.

origin_ui/advertise.go

@@ -53,7 +53,6 @@ func (server *OriginServer) CreateAdvertisement(name string, originUrl string, o
 
 	prefix := param.Origin_NamespacePrefix.GetString()
 
-	enableWrite := param.Origin_EnableWrite.GetBool()
 	// TODO: Need to figure out where to get some of these values
 	// 		 so that they aren't hardcoded...
 	nsAd := director.NamespaceAd{
@@ -65,11 +64,12 @@ func (server *OriginServer) CreateAdvertisement(name string, originUrl string, o
 		BasePath:      prefix,
 	}
 	ad = director.OriginAdvertise{
-		Name:        name,
-		URL:         originUrl,
-		WebURL:      originWebUrl,
-		Namespaces:  []director.NamespaceAd{nsAd},
-		EnableWrite: enableWrite,
+		Name:               name,
+		URL:                originUrl,
+		WebURL:             originWebUrl,
+		Namespaces:         []director.NamespaceAd{nsAd},
+		EnableWrite:        param.Origin_EnableWrite.GetBool(),
+		EnableFallbackRead: param.Origin_EnableFallbackRead.GetBool(),
 	}
 
 	return ad, nil