fix(registry): use empty strings and not nil in config

In #1858, the LRU cache was activated for registry. This exposed
an issue with how config settings are handled by docker-registry -
specifically, it doesn't appear to handle the YAML nil (`~`) value
properly. In the config parser logic in docker-registry
(see: https://github.com/deis/docker-registry/blob/2d50c1c6f396ac68858135be05dbfe41fe1898e2/docker_registry/lib/config.py#L61),
values are expected to be strings, dicts, or non-existent. The default value
when an option exists but is unset is an empty string.
This commit changes the cache config settings in
registry to use an empty string instead of ~.

Additionally, this commit also ensures that deisctl starts cache
before registry to ensure the registry is using the LRU cache.

closes #2833

Author: carmstrong

deisctl/cmd/cmd.go

@@ -184,8 +184,11 @@ func startDefaultServices(b backend.Backend, wg *sync.WaitGroup, outchan chan st
 	wg.Wait()
 
 	// optimization: start all remaining services in the background
+	// cache is a special case because it must start before registry
+	b.Start([]string{"cache"}, &_wg, _outchan, _errchan)
+	wg.Wait()
 	b.Start([]string{
-		"cache", "database", "registry@1", "controller", "builder",
+		"database", "registry@1", "controller", "builder",
 		"publisher", "router@1", "router@2", "router@3"},
 		&_wg, _outchan, _errchan)
 
@@ -269,7 +272,9 @@ func stopDefaultServices(b backend.Backend, wg *sync.WaitGroup, outchan chan str
 	wg.Wait()
 
 	outchan <- fmt.Sprintf("Control plane...")
-	b.Stop([]string{"controller", "builder", "cache", "database", "registry@1"}, wg, outchan, errchan)
+	b.Stop([]string{"controller", "builder", "database", "registry@1"}, wg, outchan, errchan)
+	wg.Wait()
+	b.Stop([]string{"cache"}, wg, outchan, errchan)
 	wg.Wait()
 
 	outchan <- fmt.Sprintf("Logging subsystem...")

registry/templates/config.yml

@@ -26,17 +26,17 @@ common: &common
         tags_cache_ttl: _env:MIRROR_TAGS_CACHE_TTL:172800 # seconds
 
     cache:
-        host: {{ or (.deis_cache_host) "~" }}
-        port: {{ or (.deis_cache_port) "~" }}
+        host: {{ or (.deis_cache_host) "" }}
+        port: {{ or (.deis_cache_port) "" }}
         password: _env:CACHE_REDIS_PASSWORD
         db: 1
 
     # Enabling LRU cache for small files
     # This speeds up read/write on small files
     # when using a remote storage backend (like S3).
     cache_lru:
-        host: {{ or (.deis_cache_host) "~" }}
-        port: {{ or (.deis_cache_port) "~" }}
+        host: {{ or (.deis_cache_host) "" }}
+        port: {{ or (.deis_cache_port) "" }}
         password: _env:CACHE_LRU_REDIS_PASSWORD
         db: 2