From d5f874c6a8c6a8e57eb4f7d95c3dcc98d47cfb7d Mon Sep 17 00:00:00 2001
From: Lukas Holecek <hluk@email.cz>
Date: Oct 05 2018 10:15:25 +0000
Subject: Check for locked DB in healthcheck


If database is locked for too long the healthcheck request should
timeout on client side (e.g. `livenessProbe` in OpenShift).

Signed-off-by: Lukas Holecek <hluk@email.cz>

---

diff --git a/waiverdb/app.py b/waiverdb/app.py
index c708fac..f1546e2 100644
--- a/waiverdb/app.py
+++ b/waiverdb/app.py
@@ -10,6 +10,7 @@ except ImportError:
 from flask import Flask, current_app
 from flask_migrate import Migrate
 from sqlalchemy import event
+from sqlalchemy.exc import ProgrammingError
 import requests
 
 from waiverdb.events import publish_new_waiver
@@ -118,9 +119,12 @@ def healthcheck():
 
     Returns a 200 response if the application is alive and able to serve requests.
     """
-    result = db.session.execute('SELECT 1').scalar()
-    if result != 1:
+    try:
+        db.session.execute("SELECT 1 FROM waiver LIMIT 0").fetchall()
+    except ProgrammingError:
+        current_app.logger.exception('Healthcheck failed on DB query.')
         raise RuntimeError('Unable to communicate with database.')
+
     return ('Health check OK', 200, [('Content-Type', 'text/plain')])