Randomize endpoints function for the router template : bz1447115

Author: Rajat Chopra

images/router/haproxy/conf/haproxy-config.template

@@ -318,7 +318,7 @@ backend be_edge_http:{{$cfgIdx}}
     {{- range $serviceUnitName, $weight := $cfg.ServiceUnitNames }}
       {{- if ne $weight 0 }}
         {{- with $serviceUnit := index $.ServiceUnits $serviceUnitName }}
-          {{- range $idx, $endpoint := endpointsForAlias $cfg $serviceUnit }}
+          {{- range $idx, $endpoint := randomEndpointsForAlias $cfg $serviceUnit true }}
             {{- if $endpoint.NoHealthCheck }}
   server {{$endpoint.ID}} {{$endpoint.IP}}:{{$endpoint.Port}} cookie {{$endpoint.IdHash}} weight {{$weight}}
             {{- else }}
@@ -387,7 +387,7 @@ backend be_tcp:{{$cfgIdx}}
     {{- range $serviceUnitName, $weight := $cfg.ServiceUnitNames }}
       {{- if ne $weight 0 }}
         {{- with $serviceUnit := index $.ServiceUnits $serviceUnitName }}
-          {{- range $idx, $endpoint := endpointsForAlias $cfg $serviceUnit }}
+          {{- range $idx, $endpoint := randomEndpointsForAlias $cfg $serviceUnit true }}
             {{- if $endpoint.NoHealthCheck }}
   server {{$endpoint.ID}} {{$endpoint.IP}}:{{$endpoint.Port}} weight {{$weight}}
             {{- else }}
@@ -405,7 +405,7 @@ backend be_tcp:{{$cfgIdx}}
                 {{- end }}
               {{- end }}
             {{- end }}
-          {{- end }}{{/* end range endpointsForAlias */}}
+          {{- end }}{{/* end range randomEndpointsForAlias */}}
         {{- end }}{{/* end get ServiceUnit from serviceUnitName */}}
       {{- end }}{{/* end if weight != 0 */}}
     {{- end }}{{/* end iterate over services*/}}
@@ -472,7 +472,7 @@ backend be_secure:{{$cfgIdx}}
     {{- range $serviceUnitName, $weight := $cfg.ServiceUnitNames }}
       {{- if ne $weight 0 }}
         {{- with $serviceUnit := index $.ServiceUnits $serviceUnitName }}
-          {{- range $idx, $endpoint := endpointsForAlias $cfg $serviceUnit }}
+          {{- range $idx, $endpoint := randomEndpointsForAlias $cfg $serviceUnit true }}
             {{- if $endpoint.NoHealthCheck }}
   server {{$endpoint.ID}} {{$endpoint.IP}}:{{$endpoint.Port}} ssl verify required ca-file {{ $workingDir }}/cacerts/{{$cfgIdx}}.pem cookie {{$endpoint.IdHash}} weight {{$weight}}
             {{- else }}
@@ -490,7 +490,7 @@ backend be_secure:{{$cfgIdx}}
                 {{- end }}
               {{- end }}{{/* end get health interval annotation */}}
             {{- end }}{{/* end else no health check */}}
-          {{- end }}{{/* end range endpointsForAlias */}}
+          {{- end }}{{/* end range randomEndpointsForAlias */}}
         {{- end }}{{/* end get serviceUnit from its name */}}
       {{- end }}{{/* end if weight != 0 */}}
     {{- end }}{{/* end range over serviceUnitNames */}}

pkg/router/template/plugin.go

@@ -100,11 +100,12 @@ func env(name, defaultValue string) string {
 func NewTemplatePlugin(cfg TemplatePluginConfig, lookupSvc ServiceLookup) (*TemplatePlugin, error) {
 	templateBaseName := filepath.Base(cfg.TemplatePath)
 	globalFuncs := template.FuncMap{
-		"endpointsForAlias": endpointsForAlias, //returns the list of valid endpoints
-		"env":               env,               //tries to get an environment variable if it can't return a default
-		"matchPattern":      matchPattern,      //anchors provided regular expression and evaluates against given string
-		"isInteger":         isInteger,         //determines if a given variable is an integer
-		"matchValues":       matchValues,       //compares a given string to a list of allowed strings
+		"endpointsForAlias":       endpointsForAlias,       //returns the list of valid endpoints
+		"randomEndpointsForAlias": randomEndpointsForAlias, //returns the list of valid endpoints
+		"env":          env,          //tries to get an environment variable if it can't return a default
+		"matchPattern": matchPattern, //anchors provided regular expression and evaluates against given string
+		"isInteger":    isInteger,    //determines if a given variable is an integer
+		"matchValues":  matchValues,  //compares a given string to a list of allowed strings
 
 		"genSubdomainWildcardRegexp": genSubdomainWildcardRegexp, //generates a regular expression matching the subdomain for hosts (and paths) with a wildcard policy
 		"generateRouteRegexp":        generateRouteRegexp,        //generates a regular expression matching the route hosts (and paths)

pkg/router/template/router.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
+	"math/rand"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -301,6 +302,17 @@ func genCertificateHostName(hostname string, wildcard bool) string {
 	return hostname
 }
 
+func randomEndpointsForAlias(alias ServiceAliasConfig, svc ServiceUnit, random bool) []Endpoint {
+        endpoints := endpointsForAlias(alias, svc)
+	if random {
+		for i := range endpoints {
+			rIndex := rand.Intn(i + 1)
+			endpoints[i], endpoints[rIndex] = endpoints[rIndex], endpoints[i]
+		}
+	}
+	return endpoints
+}
+
 func endpointsForAlias(alias ServiceAliasConfig, svc ServiceUnit) []Endpoint {
 	if len(alias.PreferPort) == 0 {
 		return svc.EndpointTable