Wrap Django RedisCache to mute exceptions (#14243)

We introduce a thin wrapper over Django's RedisCache so that the functionality of DJANGO_REDIS_IGNORE_EXCEPTIONS is retained while still being able to drop the django-redis dependency.

Credit to django-redis's implementation for the idea of using a decorator for this and abstracting out the exception handling logic.

Signed-off-by: Rick Elrod <rick@elrod.me>

awx/main/cache.py

@@ -0,0 +1,87 @@
+import functools
+
+from django.conf import settings
+from django.core.cache.backends.base import DEFAULT_TIMEOUT
+from django.core.cache.backends.redis import RedisCache
+
+from redis.exceptions import ConnectionError, ResponseError, TimeoutError
+import socket
+
+# This list comes from what django-redis ignores and the behavior we are trying
+# to retain while dropping the dependency on django-redis.
+IGNORED_EXCEPTIONS = (TimeoutError, ResponseError, ConnectionError, socket.timeout)
+
+CONNECTION_INTERRUPTED_SENTINEL = object()
+
+
+def optionally_ignore_exceptions(func=None, return_value=None):
+    if func is None:
+        return functools.partial(optionally_ignore_exceptions, return_value=return_value)
+
+    @functools.wraps(func)
+    def wrapper(*args, **kwargs):
+        try:
+            return func(*args, **kwargs)
+        except IGNORED_EXCEPTIONS as e:
+            if settings.DJANGO_REDIS_IGNORE_EXCEPTIONS:
+                return return_value
+            raise e.__cause__ or e
+
+    return wrapper
+
+
+class AWXRedisCache(RedisCache):
+    """
+    We just want to wrap the upstream RedisCache class so that we can ignore
+    the exceptions that it raises when the cache is unavailable.
+    """
+
+    @optionally_ignore_exceptions
+    def add(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
+        return super().add(key, value, timeout, version)
+
+    @optionally_ignore_exceptions(return_value=CONNECTION_INTERRUPTED_SENTINEL)
+    def _get(self, key, default=None, version=None):
+        return super().get(key, default, version)
+
+    def get(self, key, default=None, version=None):
+        value = self._get(key, default, version)
+        if value is CONNECTION_INTERRUPTED_SENTINEL:
+            return default
+        return value
+
+    @optionally_ignore_exceptions
+    def set(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
+        return super().set(key, value, timeout, version)
+
+    @optionally_ignore_exceptions
+    def touch(self, key, timeout=DEFAULT_TIMEOUT, version=None):
+        return super().touch(key, timeout, version)
+
+    @optionally_ignore_exceptions
+    def delete(self, key, version=None):
+        return super().delete(key, version)
+
+    @optionally_ignore_exceptions
+    def get_many(self, keys, version=None):
+        return super().get_many(keys, version)
+
+    @optionally_ignore_exceptions
+    def has_key(self, key, version=None):
+        return super().has_key(key, version)
+
+    @optionally_ignore_exceptions
+    def incr(self, key, delta=1, version=None):
+        return super().incr(key, delta, version)
+
+    @optionally_ignore_exceptions
+    def set_many(self, data, timeout=DEFAULT_TIMEOUT, version=None):
+        return super().set_many(data, timeout, version)
+
+    @optionally_ignore_exceptions
+    def delete_many(self, keys, version=None):
+        return super().delete_many(keys, version)
+
+    @optionally_ignore_exceptions
+    def clear(self):
+        return super().clear()

awx/settings/defaults.py

@@ -477,7 +477,7 @@ CELERYBEAT_SCHEDULE = {
 
 # Django Caching Configuration
 DJANGO_REDIS_IGNORE_EXCEPTIONS = True
-CACHES = {'default': {'BACKEND': 'django.core.cache.backends.redis.RedisCache', 'LOCATION': 'unix:/var/run/redis/redis.sock?db=1'}}
+CACHES = {'default': {'BACKEND': 'awx.main.cache.AWXRedisCache', 'LOCATION': 'unix:/var/run/redis/redis.sock?db=1'}}
 
 # Social Auth configuration.
 SOCIAL_AUTH_STRATEGY = 'social_django.strategy.DjangoStrategy'