Fixes to memcache support (#1628)

* Fix errors discovered in dev

* Log an error rather than aborting when memcache doesn't resolve
* Initialize map correctly

* Review tweaks

app/multitenant/memcache_client.go

@@ -55,7 +55,7 @@ type MemcacheClient struct {
 
 // NewMemcacheClient creates a new MemcacheClient that gets its server list
 // from SRV and updates the server list on a regular basis.
-func NewMemcacheClient(host string, timeout time.Duration, service string, updateInterval time.Duration, expiration int32) (*MemcacheClient, error) {
+func NewMemcacheClient(host string, timeout time.Duration, service string, updateInterval time.Duration, expiration int32) *MemcacheClient {
 	var servers memcache.ServerList
 	client := memcache.NewFromSelector(&servers)
 	client.Timeout = timeout
@@ -70,12 +70,12 @@ func NewMemcacheClient(host string, timeout time.Duration, service string, updat
 	}
 	err := newClient.updateMemcacheServers()
 	if err != nil {
-		return nil, err
+		log.Errorf("Error setting memcache servers to '%v': %v", host, err)
 	}
 
 	newClient.wait.Add(1)
 	go newClient.updateLoop(updateInterval)
-	return newClient, nil
+	return newClient
 }
 
 // Stop the memcache client.
@@ -169,7 +169,7 @@ func (c *MemcacheClient) FetchReports(keys []string) (map[string]report.Report,
 		}(key)
 	}
 
-	var reports map[string]report.Report
+	reports := map[string]report.Report{}
 	for i := 0; i < len(keys)-len(missing); i++ {
 		r := <-ch
 		if r.report == nil {

prog/app.go

@@ -109,21 +109,10 @@ func collectorFactory(userIDer multitenant.UserIDer, collectorURL, s3URL, natsHo
 		s3Store := multitenant.NewS3Client(s3Config, bucketName)
 		var memcacheClient *multitenant.MemcacheClient
 		if memcachedHostname != "" {
-			memcacheClient, err = multitenant.NewMemcacheClient(
+			memcacheClient = 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
-			}
 		}
 		awsCollector, err := multitenant.NewAWSCollector(
 			multitenant.AWSCollectorConfig{