Catch key errors when attempting to parse.

Also made `credentials` a key.

buildgrid/_app/commands/cmd_server.py

@@ -49,14 +49,16 @@ def start(context, config):
     with open(config) as f:
         settings = parser.get_parser().safe_load(f)
 
+    try:
         server_settings = settings['server']
         insecure_mode = server_settings['insecure-mode']
 
         credentials = None
         if not insecure_mode:
-        server_key = server_settings['tls-server-key']
-        server_cert = server_settings['tls-server-cert']
-        client_certs = server_settings['tls-client-certs']
+            credential_settings = server_settings['credentials']
+            server_key = credential_settings['tls-server-key']
+            server_cert = credential_settings['tls-server-cert']
+            client_certs = credential_settings['tls-client-certs']
             credentials = context.load_server_credentials(server_key, server_cert, client_certs)
 
             if not credentials:
@@ -64,6 +66,7 @@ def start(context, config):
                            "Set `insecure-mode: false` in order to deactivate TLS encryption.\n", err=True)
                 sys.exit(-1)
 
+        port = server_settings['port']
         instances = settings['instances']
 
         execution_controllers = _instance_maker(instances, ExecutionController)
@@ -84,7 +87,11 @@ def start(context, config):
         cas = _instance_maker(instances, ContentAddressableStorageInstance)
         bytestreams = _instance_maker(instances, ByteStreamInstance)
 
-    port = server_settings['port']
+    except KeyError as e:
+        click.echo("ERROR: Could not parse config: {}.\n".format(str(e)), err=True)
+        sys.exit(-1)
+>>>>>>> 682ac9f... Catch key errors when attempting to parse.
+
     server = BuildGridServer(port=port,
                              credentials=credentials,
                              execution_instances=execution_instances,

buildgrid/_app/settings/cas.yml

 server:
   port: 50052
   insecure-mode: true
+  credentials:
     tls-server-key: null
     tls-server-cert: null
     tls-client-certs: null

buildgrid/_app/settings/default.yml

 server:
   port: 50051
   insecure-mode: true
+  credentials:
     tls-server-key: null
     tls-server-cert: null
     tls-client-certs: null

buildgrid/_app/settings/remote-storage.yml

 server:
   port: 50051
   insecure-mode: true
+  credentials:
     tls-server-key: null
     tls-server-cert: null
     tls-client-certs: null