Add health check for node disk space

If a node runs out of disk space, nginx can no longer swap, and this can cause issues with large pushes

Fixes https://jira.coreos.com/browse/QUAY-1047

health/services.py

@@ -1,4 +1,9 @@
 import logging
+import os
+import tempfile
+
+import psutil
+
 from app import build_logs, storage, authentication, instance_keys
 from health.models_pre_oci import pre_oci_model as model
 
@@ -83,6 +88,37 @@ def _check_service_key(app):
     return (True, 'Failed to get instance key due to a database issue; skipping check')
 
 
+
+def _disk_within_threshold(path, threshold):
+  usage = psutil.disk_usage(path)
+  return (1.0 - (usage.percent / 100.0)) >= threshold
+
+
+def _check_disk_space(app):
+  """ Returns the status of the disk space for this instance. If the available disk space is below
+      a certain threshold, then will return False.
+  """
+  if not app.config.get('SETUP_COMPLETE', False):
+    return (True, 'Stack not fully setup; skipping check')
+
+  # Check the directory in which we're running.
+  currentfile = os.path.abspath(__file__)
+  if not _disk_within_threshold(currentfile, app.config.get('DISKSPACE_HEALTH_THRESHOLD', 0.1)):
+    stats = psutil.disk_usage(currentfile)
+    logger.debug('Disk space on main volume: %s', stats)
+    return (False, 'Disk space has gone below threshold on main volume: %s' % stats.percent)
+
+  # Check the temp directory as well.
+  tempdir = tempfile.gettempdir()
+  if tempdir is not None:
+    if not _disk_within_threshold(tempdir, app.config.get('DISKSPACE_HEALTH_THRESHOLD', 0.1)):
+      stats = psutil.disk_usage(tempdir)
+      logger.debug('Disk space on temp volume: %s', stats)
+      return (False, 'Disk space has gone below threshold on temp volume: %s' % stats.percent)
+
+  return (True, '')
+
+
 _SERVICES = {
   'registry_gunicorn': _check_gunicorn('v1/_internal_ping'),
   'web_gunicorn': _check_gunicorn('_internal_ping'),
@@ -92,6 +128,7 @@ _SERVICES = {
   'storage': _check_storage,
   'auth': _check_auth,
   'service_key': _check_service_key,
+  'disk_space': _check_disk_space,
 }
 
 def check_all_services(app, skip):