Add health check endpoint to verify that the locally running DB revision matches that of the database

Fixes #132

Dockerfile

@@ -55,6 +55,8 @@ RUN mkdir /usr/local/nginx/logs/
 RUN TEST=true venv/bin/python -m unittest discover -f
 RUN TEST=true venv/bin/python -m test.registry_tests -f
 
+RUN PYTHONPATH=. venv/bin/alembic heads > ALEMBIC_HEAD
+
 VOLUME ["/conf/stack", "/var/log", "/datastorage", "/tmp", "/conf/etcd"]
 
 EXPOSE 443 8443 80

endpoints/web.py

@@ -8,6 +8,7 @@ from urlparse import urlparse
 from health.healthcheck import get_healthchecker
 
 from data import model
+from data.database import db
 from data.model.oauth import DatabaseAuthorizationProvider
 from app import app, billing as stripe, build_logs, avatar, signer, log_archive
 from auth.auth import require_session_login, process_oauth
@@ -227,6 +228,30 @@ def endtoend_health():
   return response
 
 
+@web.route('/health/dbrevision', methods=['GET'])
+@route_show_if(features.BILLING)
+@no_cache
+def dbrevision_health():
+  # Find the revision from the database.
+  result = db.execute_sql('select * from alembic_version limit 1').fetchone()
+  db_revision = result[0]
+
+  # Find the local revision from the file system.
+  with open('ALEMBIC_HEAD', 'r') as f:
+    local_revision = f.readline().split(' ')[0]
+
+  data = {
+    'db_revision': db_revision,
+    'local_revision': local_revision,
+  }
+
+  status_code = 200 if db_revision == local_revision else 400
+
+  response = jsonify(dict(data=data, status_code=status_code))
+  response.status_code = status_code
+  return response
+
+
 @web.route('/tos', methods=['GET'])
 @no_cache
 def tos():