Add pre_ping to sqlalchemy create_engine option (#400)

Basically allows reconnection for lost DB connections.
Configurable with default `False`.

* adding pre_ping to sqlalchemy create_engine optin

* add the engine options as a configurable option

* Addressing review for PR#400

* use default value from os.env

* fixing syntax

Dockerfile

@@ -21,6 +21,7 @@ ENV LC_ALL="en_US.UTF-8" \
 	ADMIN_PWD=admin \
 	ADMIN_EMAIL=admin.istrator@mydomain.com \
 	SQLALCHEMY_DATABASE_URI='sqlite:////GeoHealthCheck/DB/data.db' \
+	SQLALCHEMY_ENGINE_OPTION_PRE_PING=False \
 	SECRET_KEY='d544ccc37dc3ad214c09b1b7faaa64c60351d5c8bb48b342' \
 	GHC_PROBE_HTTP_TIMEOUT_SECS=30 \
 	GHC_MINIMAL_RUN_FREQUENCY_MINS=10 \

GeoHealthCheck/config_main.py

@@ -30,6 +30,7 @@
 DEBUG = False
 SQLALCHEMY_ECHO = False
 SQLALCHEMY_TRACK_MODIFICATIONS = False
+SQLALCHEMY_ENGINE_OPTION_PRE_PING = False
 SQLALCHEMY_DATABASE_URI = 'sqlite:///data.db'
 # Alternative configuration for PostgreSQL database
 # SQLALCHEMY_DATABASE_URI = 'postgresql://user:password@host:port/database'

GeoHealthCheck/init.py

@@ -83,8 +83,13 @@ def init():
             app.config['GHC_SITE_URL'].rstrip('/')
 
         app.secret_key = app.config['SECRET_KEY']
-
-        App.db_instance = SQLAlchemy(app)
+        SQLALCHEMY_ENGINE_OPTIONS = {
+                                 'pool_pre_ping': app.config[
+                                     'SQLALCHEMY_ENGINE_OPTION_PRE_PING'
+                                     ]
+                                 }
+        App.db_instance = SQLAlchemy(app,
+                                     engine_options=SQLALCHEMY_ENGINE_OPTIONS)
         App.babel_instance = Babel(app)
 
         # Plugins (via Docker ENV) must be list, but may have been

docker/config_site.py

@@ -40,7 +40,8 @@ def str2bool(v):
 # makes it easier to override via Docker "environment"
 # settings on running GHC Containers.
 SQLALCHEMY_DATABASE_URI = os.environ['SQLALCHEMY_DATABASE_URI']
-
+# When True enables 'pre_ping' (optionally reconnect to DB) for the SQLALCHEMY create_engine options
+SQLALCHEMY_ENGINE_OPTION_PRE_PING = os.environ['SQLALCHEMY_ENGINE_OPTION_PRE_PING']
 # Replace None with 'your secret key string' in quotes
 SECRET_KEY = os.environ['SECRET_KEY']
 

docs/config.rst

@@ -14,6 +14,7 @@ a configuration file in the environment settings that will override settings in
 The configuration options are:
 
 - **SQLALCHEMY_DATABASE_URI**: the database configuration.  See the SQLAlchemy documentation for more info
+- **SQLALCHEMY_ENGINE_OPTION_PRE_PING**: DB Disconnect Handling, emitting a test statement on the SQL connection at the start of each connection pool checkout (default: ``False``)
 - **SECRET_KEY**: secret key to set when enabling authentication. Use the output of ``paver create_secret_key`` to set this value
 - **GHC_RETENTION_DAYS**: the number of days to keep Run history
 - **GHC_PROBE_HTTP_TIMEOUT_SECS**: stop waiting for the first byte of a Probe response after the given number of seconds