Pass in memcache client

app/multitenant/dynamo_collector.go

@@ -23,14 +23,12 @@ import (
 )
 
 const (
-	hourField              = "hour"
-	tsField                = "ts"
-	reportField            = "report"
-	reportCacheSize        = (15 / 3) * 10 * 5 // (window size * report rate) * number of hosts per user * number of users
-	reportCacheExpiration  = 15 * time.Second
-	memcacheExpiration     = 15 // seconds
-	memcacheUpdateInterval = 1 * time.Minute
-	natsTimeout            = 10 * time.Second
+	hourField             = "hour"
+	tsField               = "ts"
+	reportField           = "report"
+	reportCacheSize       = (15 / 3) * 10 * 5 // (window size * report rate) * number of hosts per user * number of users
+	reportCacheExpiration = 15 * time.Second
+	natsTimeout           = 10 * time.Second
 )
 
 var (
@@ -130,8 +128,8 @@ func NewDynamoDBCollector(
 	userIDer UserIDer,
 	dynamoDBConfig *aws.Config, tableName string,
 	s3Store *S3Store,
-	natsHost,
-	memcachedHost string, memcachedTimeout time.Duration, memcachedService string,
+	natsHost string,
+	memcacheClient *MemcacheClient,
 ) (DynamoDBCollector, error) {
 	var nc *nats.Conn
 	if natsHost != "" {
@@ -142,22 +140,6 @@ func NewDynamoDBCollector(
 		}
 	}
 
-	var memcacheClient *MemcacheClient
-	if memcachedHost != "" {
-		var err error
-		memcacheClient, err = NewMemcacheClient(memcachedHost, memcachedTimeout, memcachedService, memcacheUpdateInterval, memcacheExpiration)
-		if err != nil {
-			// TODO(jml): Ideally, we wouldn't abort here, we would instead
-			// log errors when we try to use the memcache & fail to do so, as
-			// aborting here introduces ordering dependencies into our
-			// deployment.
-			//
-			// Note: this error only happens when either the memcachedHost or
-			// any of the SRV records that it points to fail to resolve.
-			return nil, err
-		}
-	}
-
 	return &dynamoDBCollector{
 		db:        dynamodb.New(session.New(dynamoDBConfig)),
 		s3:        s3Store,

prog/app.go

@@ -27,6 +27,11 @@ import (
 	"github.com/weaveworks/scope/probe/docker"
 )
 
+const (
+	memcacheExpiration     = 15 // seconds
+	memcacheUpdateInterval = 1 * time.Minute
+)
+
 var (
 	requestDuration = prometheus.NewSummaryVec(prometheus.SummaryOpts{
 		Namespace: "scope",
@@ -100,11 +105,29 @@ func collectorFactory(userIDer multitenant.UserIDer, collectorURL, s3URL, natsHo
 			return nil, err
 		}
 		bucketName := strings.TrimPrefix(s3.Path, "/")
-		s3Store := multitenant.NewS3Client(s3Config, bucketName)
 		tableName := strings.TrimPrefix(parsed.Path, "/")
+		s3Store := multitenant.NewS3Client(s3Config, bucketName)
+		var memcacheClient *multitenant.MemcacheClient
+		if memcachedHostname != "" {
+			memcacheClient, err = multitenant.NewMemcacheClient(
+				memcachedHostname, memcachedTimeout, memcachedService,
+				memcacheUpdateInterval, memcacheExpiration,
+			)
+			if err != nil {
+				// TODO(jml): Ideally, we wouldn't abort here, we would instead
+				// log errors when we try to use the memcache & fail to do so, as
+				// aborting here introduces ordering dependencies into our
+				// deployment.
+				//
+				// Note: this error only happens when either the memcachedHost
+				// or any of the SRV records that it points to fail to
+				// resolve.
+				return nil, err
+			}
+		}
 		dynamoCollector, err := multitenant.NewDynamoDBCollector(
 			userIDer, dynamoDBConfig, tableName, &s3Store, natsHostname,
-			memcachedHostname, memcachedTimeout, memcachedService,
+			memcacheClient,
 		)
 		if err != nil {
 			return nil, err