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Added a DynamoDb backend to contrib
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@ajenkinski
ajenkinski committed Apr 4, 2022
1 parent 25cebaa commit fea1bbb
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1 change: 1 addition & 0 deletions CHANGES.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@ Version 1.2.0
Unreleased

- cachelib is now used as backend. PR `#308 <https://github.com/pallets-eco/flask-caching/pull/308>`_.
- A ``DynamoDbCache`` backend has been add to the user contributed backends.


Version 1.10.1
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129 changes: 81 additions & 48 deletions src/flask_caching/contrib/dynamodbcache.py
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Original file line number Diff line number Diff line change
Expand Up @@ -21,24 +21,34 @@ def utcnow():

class DynamoDbCache(BaseCache):
"""
Implementation of flask_caching.BaseCache that uses an AWS DynamoDb table as the backend.
Implementation of flask_caching.BaseCache that uses an AWS DynamoDb table
as the backend.
The DynamoDB table is required to already exist. The table must be defined with a hash_key of type string, and
no sort key. Additionally, you'll probably want to enable the TTL feature on the table, so that DynamoDB will
automatically delete expired cache items. The hash_key attribute name defaults to 'cache_key', and the ttl
attribute name defaults to 'expiration_time'. These defaults can be changed via constructor parameter, or via
app config properties.
The DynamoDB table is required to already exist. The table must be
defined with a hash_key of type string, and no sort key. Additionally,
you'll probably want to enable the TTL feature on the table, so that
DynamoDB will automatically delete expired cache items. The hash_key
attribute name defaults to 'cache_key', and the ttl attribute name
defaults to 'expiration_time'. These defaults can be changed via
constructor parameter, or via app config properties.
Your server process will require dynamodb:GetItem and dynamodb:PutItem IAM permissions on the cache table.
Your server process will require dynamodb:GetItem and dynamodb:PutItem
IAM permissions on the cache table.
App config: The factory method for this class uses the following app
config attributes:
App config: The factory method for this class uses the following app config attributes:
CACHE_DYNAMODB_TABLE: (Required) the name of the DynamoDB table to use
CACHE_DYNAMODB_KEY_FIELD: The name of the hash key attribute of the table. Defaults to 'cache_key'
CACHE_DYNAMODB_EXPIRATION_TIME_FIELD: The name of the TTL field. Defaults to 'expiration_time'
CACHE_DYNAMODB_KEY_FIELD: The name of the hash key attribute of the
table. Defaults to 'cache_key'
CACHE_DYNAMODB_EXPIRATION_TIME_FIELD: The name of the TTL field. Defaults
to 'expiration_time'
Additionally, the CACHE_DEFAULT_TIMEOUT attribute can be used to override default the cache timeout.
Additionally, the CACHE_DEFAULT_TIMEOUT attribute can be used to override
default the cache timeout.
Here is how you could create a DynamoDB table suitable for use by this class using the AWS CLI.
Here is how you could create a DynamoDB table suitable for use by this
class using the AWS CLI.
TABLE_NAME=cache-table
KEY_ATTRIBUTE=cache_key
Expand All @@ -54,18 +64,27 @@ class DynamoDbCache(BaseCache):
--table-name $TABLE_NAME \
--time-to-live-specification Enabled=true,AttributeName=$TTL_ATTRIBUTE
If you use anything other than the default key and TTL attribute names, be sure to update the app config
appropriately.
If you use anything other than the default key and TTL attribute names,
be sure to update the app config appropriately.
Limitations: DynamoDB table items are limited to 400 KB in size. Since
this class stores cached items in a table, the max size of a cache entry
will be slightly less than 400 KB, since the cache key and expiration
time fields are also part of the item.
:param table_name: The name of the DynamoDB table to use
:param default_timeout: Set the timeout in seconds after which cache entries expire
:param key_field: The name of the hash_key attribute in the DynamoDb table. This must be a string attribute.
:param expiration_time_field: The name of the table attribute to store the expiration time in. This will be an
int attribute. The timestamp will be stored as seconds past the epoch. If you
configure this as the TTL field, then DynamoDB will automatically delete expired
entries.
:param dynamo: A boto3 dynamodb resource object. This is mainly for testing; by default the class will create its
own resource object.
:param default_timeout: Set the timeout in seconds after which cache entries
expire
:param key_field: The name of the hash_key attribute in the DynamoDb
table. This must be a string attribute.
:param expiration_time_field: The name of the table attribute to store the
expiration time in. This will be an int
attribute. The timestamp will be stored as
seconds past the epoch. If you configure
this as the TTL field, then DynamoDB will
automatically delete expired entries.
:param dynamo: A boto3 dynamodb resource object. This is mainly for testing;
by default the class will create its own resource object.
"""

def __init__(
Expand Down Expand Up @@ -93,7 +112,8 @@ def __init__(
def factory(cls, app, config, args: list, kwargs: dict):
args.insert(0, config['CACHE_DYNAMODB_TABLE'])
key_field = config.get('CACHE_DYNAMODB_KEY_FIELD')
expiration_time_field = config.get('CACHE_DYNAMODB_EXPIRATION_TIME_FIELD')
expiration_time_field = config.get(
'CACHE_DYNAMODB_EXPIRATION_TIME_FIELD')

if key_field:
kwargs.setdefault('key_field', key_field)
Expand All @@ -104,13 +124,17 @@ def factory(cls, app, config, args: list, kwargs: dict):

def _get_item(self, key, attributes=None):
"""
Get an item from the cache table, optionally limiting the returned attributes.
Get an item from the cache table, optionally limiting the returned
attributes.
:param key: The cache key of the item to fetch
:param attributes: An optional list of attributes to fetch. If not given, all attributes are fetched. The
expiration_time field will always be added to the list of fetched attributes.
:return: The table item for key if it exists and is not expired, else None
:param attributes: An optional list of attributes to fetch. If not
given, all attributes are fetched. The
expiration_time field will always be added to the
list of fetched attributes.
:return: The table item for key if it exists and is not expired, else
None
"""
kwargs = {}
if attributes:
Expand All @@ -133,20 +157,24 @@ def get(self, key):
Get a cache item as a Flask Response
:param key: The cache key of the item to fetch
:return: If key is found and the item isn't expired, returns a Flask response object containing the cached
response body, status code, and headers. Else returns None
:return: If key is found and the item isn't expired, returns a Flask
response object containing the cached response body, status
code, and headers. Else returns None
"""
cache_item = self._get_item(key)
if cache_item:
response = cache_item[RESPONSE_FIELD]
return flask.make_response(bytes(response['body']), int(response['statusCode']), response['headers'])
return flask.make_response(
bytes(response['body']),
int(response['statusCode']),
response['headers'])

return None

def delete(self, key):
"""
Deletes an item from the cache. This is a no-op if the item doesn't exist
Deletes an item from the cache. This is a no-op if the item doesn't
exist
:param key: Key of the item to delete.
:return: True if the key existed and was deleted
Expand All @@ -166,13 +194,16 @@ def _set(self, key, value, timeout=None, overwrite=True):
:param key: Cache key to use
:param value: A value returned by a flask view function
:param timeout: The timeout in seconds for the cached item, to override the default
:param overwrite: If true, overwrite any existing cache item with key. If false, the new value will only be
stored if no non-expired cache item exists with key.
:param timeout: The timeout in seconds for the cached item, to override
the default
:param overwrite: If true, overwrite any existing cache item with key.
If false, the new value will only be stored if no
non-expired cache item exists with key.
:return: True if the new item was stored.
"""
now = utcnow()
expiration_time = now + datetime.timedelta(seconds=self._normalize_timeout(timeout))
expiration_time = now + datetime.timedelta(
seconds=self._normalize_timeout(timeout))
response_obj = flask.make_response(value)

cached_response = {
Expand All @@ -183,20 +214,20 @@ def _set(self, key, value, timeout=None, overwrite=True):

kwargs = {}
if not overwrite:
# Cause the put to fail if a non-expired item with this key already exists
cond = Attr(self._key_field).not_exists() | Attr(self._expiration_time_field).lte(int(now.timestamp()))
# Cause the put to fail if a non-expired item with this key
# already exists
cond = Attr(self._key_field).not_exists() \
| Attr(self._expiration_time_field).lte(int(now.timestamp()))
kwargs = dict(ConditionExpression=cond)

try:
self._table.put_item(
Item={
self._key_field: key,
self._expiration_time_field: int(expiration_time.timestamp()),
CREATED_AT_FIELD: now.isoformat(),
RESPONSE_FIELD: cached_response
},
**kwargs
)
item = {
self._key_field: key,
self._expiration_time_field: int(expiration_time.timestamp()),
CREATED_AT_FIELD: now.isoformat(),
RESPONSE_FIELD: cached_response
}
self._table.put_item(Item=item, **kwargs)
return True
except self._dynamo.meta.client.exceptions.ConditionalCheckFailedException:
return False
Expand All @@ -212,9 +243,11 @@ def has(self, key):

def clear(self):
paginator = self._dynamo.meta.client.get_paginator('scan')
pages = paginator.paginate(TableName=self._table_name,
ProjectionExpression=self._key_field)

with self._table.batch_writer() as batch:
for page in paginator.paginate(TableName=self._table_name, ProjectionExpression=self._key_field):
for page in pages:
for item in page['Items']:
batch.delete_item(Key=item)

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