use GAE lib_config for configuration, all config in settings.py

main.py

@@ -22,18 +22,22 @@
 import jinja2
 import webapp2
 from apiclient.discovery import build
+from google.appengine.api import lib_config
 from google.appengine.api import memcache
 from oauth2client.appengine import AppAssertionCredentials
 
 SAMPLE_NAME = 'Instance timeout helper'
-# Be careful, this application will delete instances unless they're tagged
-# with one of the SAFE_TAGS below.
-GCE_PROJECT_ID = 'replace-with-your-compute-engine-project-id'
-TIMEOUT = 60 * 8  # in minutes, defaulting to 8 hours
-SAFE_TAGS = "production safetag".lower().split()
-# In pretend mode, deletes are only logged. Set this to False after you've
-# double-checked the status page and you're ready to enable the deletes.
-DRY_RUN = True
+
+# To make configuration changes, update these values in settings.py
+CONFIG_DEFAULTS = {
+    'DRY_RUN': True,
+    'GCE_PROJECT_ID': 'replace-with-your-compute-engine-project-id',
+    'SAFE_TAGS': ['production', 'safetag'],
+    'TIMEOUT': 60 * 8,  # in minutes, defaulting to 8 hours
+}
+registry = lib_config.LibConfigRegistry('settings')
+config = registry.register('main', CONFIG_DEFAULTS)
+config.SAFE_TAGS = [t.lower() for t in config.SAFE_TAGS]
 
 # Obtain App Engine AppAssertion credentials and authorize HTTP connection.
 # https://developers.google.com/appengine/docs/python/appidentity/overview
@@ -54,7 +58,7 @@ def annotate_instances(instances):
         # set _excluded
         excluded = False
         for tag in instance.get('tags', []):
-            if tag.lower() in SAFE_TAGS:
+            if tag.lower() in config.SAFE_TAGS:
                 excluded = True
                 break
         instance['_excluded'] = excluded
@@ -65,15 +69,15 @@ def annotate_instances(instances):
         now = datetime.datetime.now()
         delta = now - creation
         instance['_age_hours'] = delta.seconds / 60
-        if delta.seconds > TIMEOUT * 60 and not instance['_excluded']:
+        if delta.seconds > config.TIMEOUT * 60 and not instance['_excluded']:
             instance['_timeout_expired'] = True
         else:
             instance['_timeout_expired'] = False
 
 
 def list_instances():
     """returns a list of dictionaries containing GCE instance data"""
-    request = compute.instances().list(project=GCE_PROJECT_ID)
+    request = compute.instances().list(project=config.GCE_PROJECT_ID)
     response = request.execute()
     instances = response.get('items', [])
     annotate_instances(instances)
@@ -85,11 +89,6 @@ class MainHandler(webapp2.RequestHandler):
     def get(self):
         instances = list_instances()
 
-        config = {}
-        config['DRY_RUN'] = DRY_RUN
-        config['SAFE_TAGS'] = ', '.join(SAFE_TAGS)
-        config['TIMEOUT'] = TIMEOUT
-        config['GCE_PROJECT_ID'] = GCE_PROJECT_ID
         data = {}
         data['config'] = config
         data['title'] = SAMPLE_NAME
@@ -112,11 +111,11 @@ def delete_expired_instances():
 
     for instance in instances:
         name = instance['name']
-        if DRY_RUN:
+        if config.DRY_RUN:
             logging.info("DRY_RUN, not deleted: %s", name)
         else:
             logging.info("DELETE: %s", name)
-            request = compute.instances().delete(project=GCE_PROJECT_ID,
+            request = compute.instances().delete(project=config.GCE_PROJECT_ID,
                                                  instance=name)
             response = request.execute()
             logging.info(response)

settings.py

@@ -0,0 +1,13 @@
+# In DRY_RUN mode, deletes are only logged. Set this to False after you've
+# double-checked the status page and you're ready to enable the deletes.
+main_DRY_RUN = True
+
+# Be careful, this application will delete all instances in this project 
+# unless they're tagged with one of the SAFE_TAGS below.
+main_GCE_PROJECT_ID = 'replace-with-your-compute-engine-project-id'
+
+# Instance tags which will never be deleted.
+main_SAFE_TAGS = ['production', 'safetag']
+
+# Instances are deleted after they have been running for TIMEOUT minutes.
+main_TIMEOUT = 60 * 8  # in minutes, defaulting to 8 hours

templates/index.html

@@ -21,9 +21,12 @@
     <body>
         <h1>{{title}}</h1>
         <h2>Configuration:</h2>
-        {% for key, value in config.items() %}
-        <li>{{key}} : {{value}}
-        {% endfor %}
+        <ul>
+            <li>DRY_RUN: {{config.DRY_RUN}}
+            <li>GCE_PROJECT_ID: {{config.GCE_PROJECT_ID}}
+            <li>SAFE_TAGS: {{', '.join(config.SAFE_TAGS)}}
+            <li>TIMEOUT: {{config.TIMEOUT}}
+        </ul>
         <h2>Instances:</h2>
         <table>
             <thead>