Process environment variables with python-decouple (#22)

* Use python-decouple for environment variable management in scale.py

* update dockerfile to optimize image size

* do not crash when scale_resource gets a 404.

Dockerfile

@@ -1,10 +1,10 @@
-FROM python:3.6
+FROM python:3.6-alpine
 
 WORKDIR /usr/src/app
 
 COPY requirements.txt .
 
-RUN pip install -r requirements.txt
+RUN pip install --no-cache-dir -r requirements.txt
 
 COPY . .
 

autoscaler/autoscaler.py

@@ -338,8 +338,13 @@ def scale_resources(self):
                               str(resource_type).capitalize(), name,
                               namespace, current_pods, desired_pods)
 
-            self.scale_resource(desired_pods, current_pods,
-                                resource_type, namespace, name)
+            try:
+                self.scale_resource(desired_pods, current_pods,
+                                    resource_type, namespace, name)
+            except kubernetes.client.rest.ApiException as err:
+                self.logger.warning('Failed to scale %s `%s.%s` due to %s: %s',
+                                    resource_type, namespace, name,
+                                    type(err).__name__, err)
 
     def scale(self):
         self.tally_queues()

autoscaler/autoscaler_test.py

@@ -274,6 +274,13 @@ def test_scale_resources(self):
         scaler.get_desired_pods = lambda *x: 4
         scaler.scale_resources()
 
+        # test failure to scale does not crash
+        def fail_to_scale(*_, **__):
+            raise kubernetes.client.rest.ApiException(404)
+
+        scaler.scale_resource = fail_to_scale
+        scaler.scale_resources()
+
         # same delimiter throws an error;
         with pytest.raises(ValueError):
             param_delim = '|'

requirements.txt

@@ -1,2 +1,3 @@
-redis==3.2.1
 kubernetes==9.0.0
+python-decouple>=3.1,<4
+redis==3.2.1

scale.py

@@ -28,11 +28,12 @@
 from __future__ import division
 from __future__ import print_function
 
-import os
-import sys
-import time
 import logging
 import logging.handlers
+import sys
+import time
+
+import decouple
 
 import autoscaler
 
@@ -70,15 +71,15 @@ def initialize_logger(debug_mode=True):
     _logger = logging.getLogger(__file__)
 
     REDIS_CLIENT = autoscaler.redis.RedisClient(
-        host=os.getenv('REDIS_HOST'),
-        port=os.getenv('REDIS_PORT'),
-        backoff=int(os.getenv('REDIS_INTERVAL', '1')))
+        host=decouple.config('REDIS_HOST', cast=str),
+        port=decouple.config('REDIS_PORT', default=6379, cast=int),
+        backoff=decouple.config('REDIS_INTERVAL', default=1, cast=int))
 
     SCALER = autoscaler.Autoscaler(
         redis_client=REDIS_CLIENT,
-        scaling_config=os.getenv('AUTOSCALING'))
+        scaling_config=decouple.config('AUTOSCALING'))
 
-    INTERVAL = int(os.getenv('INTERVAL', '5'))
+    INTERVAL = decouple.config('INTERVAL', default=5, cast=int)
 
     while True:
         try: