Enable customization of Patroni Kubernetes labels. (#230)

Add environment variables to customize names and values of labels used
by Patroni on Kubernets to locate its metadata. At least one of those
labels (cluster name) has different default value between Spilo
('version'), Patroni and the postgres-operator ('cluster-name').  This
change allows passing the operator label names directly to Spilo (and
Patroni), w/o relying on defaults to match.

ENVIRONMENT.rst

@@ -34,3 +34,8 @@ Environment Configuration Settings
 - **WAL_GCS_BUCKET**: ditto for the Google Cloud Storage (WAL-E supports both S3 and GCS).
 - **GOOGLE_APPLICATION_CREDENTIALS**: credentials for WAL-E when running in Google Cloud.
 - **CALLBACK_SCRIPT**: the callback script to run on various cluster actions (on start, on stop, on restart, on role change). The script will receive the cluster name, connection string and the current action. See `Patroni <http://patroni.readthedocs.io/en/latest/SETTINGS.html?highlight=callback#postgresql>`__ documentation for details.
+- **DCS_ENABLE_KUBERNETES_API**: a non-empty value forces Patroni to use Kubernetes as a DCS. Default is empty.
+- **KUBERNETES_USE_CONFIGMAPS**: a non-empty value makes Patroni store its metadata in ConfigMaps instead of Endpoints when running on Kubernetes. Default is empty.
+- **KUBERNETES_ROLE_LABEL**: name of the label containing Postgres role when running on Kubernetens. Default is 'spilo-role'.
+- **KUBERNETES_SCOPE_LABEL**: name of the label containing cluster name. Default is 'version'.
+- **KUBERNETES_LABELS**: a JSON describing names and values of other labels used by Patroni on Kubernetes to locate its metadata. Default is '{"application": "spilo"}'.

postgres-appliance/configure_spilo.py

@@ -2,6 +2,7 @@
 # -*- coding: utf-8 -*-
 
 import argparse
+import json
 import logging
 import re
 import os
@@ -23,6 +24,7 @@
 PROVIDER_LOCAL = "local"
 PROVIDER_UNSUPPORTED = "unsupported"
 USE_KUBERNETES = os.environ.get('KUBERNETES_SERVICE_HOST') is not None
+KUBERNETES_DEFAULT_LABELS = '{"application": "spilo"}'
 MEMORY_LIMIT_IN_BYTES_PATH = '/sys/fs/cgroup/memory/memory.limit_in_bytes'
 
 
@@ -369,6 +371,9 @@ def get_placeholders(provider):
     placeholders.setdefault('PAM_OAUTH2', '')
     placeholders.setdefault('CALLBACK_SCRIPT', '')
     placeholders.setdefault('DCS_ENABLE_KUBERNETES_API', '')
+    placeholders.setdefault('KUBERNETES_ROLE_LABEL', 'spilo-role')
+    placeholders.setdefault('KUBERNETES_SCOPE_LABEL', 'version')
+    placeholders.setdefault('KUBERNETES_LABELS', KUBERNETES_DEFAULT_LABELS)
     placeholders.setdefault('KUBERNETES_USE_CONFIGMAPS', '')
     placeholders.setdefault('USE_PAUSE_AT_RECOVERY_TARGET', False)
     placeholders.setdefault('CLONE_METHOD', '')
@@ -447,8 +452,16 @@ def pystache_render(*args, **kwargs):
 
 def get_dcs_config(config, placeholders):
     if USE_KUBERNETES and placeholders.get('DCS_ENABLE_KUBERNETES_API'):
-        config = {'kubernetes': {'role_label': 'spilo-role', 'scope_label': 'version',
-                                 'labels': {'application': 'spilo'}}}
+        try:
+            kubernetes_labels = json.loads(placeholders.get('KUBERNETES_LABELS'))
+        except (TypeError, ValueError) as e:
+            logging.warning("could not parse kubernetes labels as a JSON: {0}, "
+                            "reverting to the default: {1}".format(e, KUBERNETES_DEFAULT_LABELS))
+            kubernetes_labels = json.loads(KUBERNETES_DEFAULT_LABELS)
+
+        config = {'kubernetes': {'role_label': placeholders.get('KUBERNETES_ROLE_LABEL'),
+                                 'scope_label': placeholders.get('KUBERNETES_SCOPE_LABEL'),
+                                 'labels': kubernetes_labels}}
         if not placeholders.get('KUBERNETES_USE_CONFIGMAPS'):
             config['kubernetes'].update({'use_endpoints': True, 'pod_ip': placeholders['instance_data']['ip'],
                                          'ports': [{'port': 5432, 'name': 'postgresql'}]})