Microsoft Azure Event Hubs checkpointer implementation with Blob Storage Client Library for Python
Azure EventHubs Checkpoint Store client library for Python using Storage Blobs
Azure EventHubs Checkpoint Store is used for storing checkpoints while processing events from Azure Event Hubs.
This Checkpoint Store package works as a plug-in package to
EventHubConsumerClient. It uses Azure Storage Blob as the persistent store for maintaining checkpoints and partition ownership information.
Please note that this is an async library, for sync version of the Azure EventHubs Checkpoint Store client library, please refer to azure-eventhub-checkpointstoreblob.
Python 3.5.3 or later.
Microsoft Azure Subscription: To use Azure services, including Azure Event Hubs, you'll need a subscription. If you do not have an existing Azure account, you may sign up for a free trial or use your MSDN subscriber benefits when you create an account.
Event Hubs namespace with an Event Hub: To interact with Azure Event Hubs, you'll also need to have a namespace and Event Hub available. If you are not familiar with creating Azure resources, you may wish to follow the step-by-step guide for creating an Event Hub using the Azure portal. There, you can also find detailed instructions for using the Azure CLI, Azure PowerShell, or Azure Resource Manager (ARM) templates to create an Event Hub.
Azure Storage Account: You'll need to have an Azure Storage Account and create a Azure Blob Storage Block Container to store the checkpoint data with blobs. You may follow the guide creating an Azure Block Blob Storage Account.
Install the package
$ pip install azure-eventhub-checkpointstoreblob-aio
Checkpointing is a process by which readers mark or commit their position within a partition event sequence. Checkpointing is the responsibility of the consumer and occurs on a per-partition basis within a consumer group. This responsibility means that for each consumer group, each partition reader must keep track of its current position in the event stream, and can inform the service when it considers the data stream complete. If a reader disconnects from a partition, when it reconnects it begins reading at the checkpoint that was previously submitted by the last reader of that partition in that consumer group. When the reader connects, it passes the offset to the event hub to specify the location at which to start reading. In this way, you can use checkpointing to both mark events as "complete" by downstream applications, and to provide resiliency if a failover between readers running on different machines occurs. It is possible to return to older data by specifying a lower offset from this checkpointing process. Through this mechanism, checkpointing enables both failover resiliency and event stream replay.
Offsets & sequence numbers
Both offset & sequence number refer to the position of an event within a partition. You can think of them as a client-side cursor. The offset is a byte numbering of the event. The offset/sequence number enables an event consumer (reader) to specify a point in the event stream from which they want to begin reading events. You can specify a timestamp such that you receive events enqueued only after the given timestamp. Consumers are responsible for storing their own offset values outside of the Event Hubs service. Within a partition, each event includes an offset, sequence number and the timestamp of when it was enqueued.
The easiest way to create a
EventHubConsumerClient is to use a connection string.
from azure.eventhub.aio import EventHubConsumerClient eventhub_client = EventHubConsumerClient.from_connection_string("my_eventhub_namespace_connection_string", "my_consumer_group", eventhub_name="my_eventhub")
For other ways of creating a
EventHubConsumerClient, refer to EventHubs library for more details.
Consume events using a
BlobCheckpointStore to do checkpoint
import asyncio from azure.eventhub.aio import EventHubConsumerClient from azure.eventhub.extensions.checkpointstoreblobaio import BlobCheckpointStore connection_str = '<< CONNECTION STRING FOR THE EVENT HUBS NAMESPACE >>' consumer_group = '<< CONSUMER GROUP >>' eventhub_name = '<< NAME OF THE EVENT HUB >>' storage_connection_str = '<< CONNECTION STRING OF THE STORAGE >>' container_name = '<< STORAGE CONTAINER NAME>>' async def on_event(partition_context, event): # Put your code here. await partition_context.update_checkpoint(event) # Or update_checkpoint every N events for better performance. async def main(): checkpoint_store = BlobCheckpointStore.from_connection_string( storage_connection_str, container_name ) client = EventHubConsumerClient.from_connection_string( connection_str, consumer_group, eventhub_name=eventhub_name, checkpoint_store=checkpoint_store, ) async with client: await client.receive(on_event) if __name__ == '__main__': loop = asyncio.get_event_loop() loop.run_until_complete(main())
BlobCheckpointStore with a different version of Azure Storage Service API
Some environments have different versions of Azure Storage Service API.
BlobCheckpointStore by default uses the Storage Service API version 2019-07-07. To use it against a different
api_version when you create the
Enabling logging will be helpful to do trouble shooting.
azure.eventhub.extensions.checkpointstoreblobaiologger to collect traces from the library.
azure.eventhublogger to collect traces from the main azure-eventhub library.
azure.eventhub.extensions.checkpointstoreblobaio._vendor.storagelogger to collect traces from azure storage blob library.
uamqplogger to collect traces from the underlying uAMQP library.
- Enable AMQP frame level trace by setting
logging_enable=Truewhen creating the client.
- https://github.com/Azure/azure-sdk-for-python/blob/master/sdk/eventhub/azure-eventhub-checkpointstoreblob-aio/samples/receive_events_using_checkpoint_store_async.py - EventHubConsumerClient with blob checkpoint store example
- https://github.com/Azure/azure-sdk-for-python/blob/master/sdk/eventhub/azure-eventhub-checkpointstoreblob-aio/samples/receive_events_using_checkpoint_store_storage_api_version_async.py - EventHubConsumerClient with blob checkpoint store and storage version example
Reference documentation is available here
If you encounter any bugs or have suggestions, please file an issue in the Issues section of the project.
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- Fixed a bug that
KeyErrordue to reading empty metadata of parent node when working with Data Lake enabled Blob Storage.
- Fixed a bug that may gradually slow down retrieving checkpoint data from the storage blob if the storage account "File share soft delete" is enabled. #12836
BlobCheckpointStorenow supports older versions of Azure Storage Service API.
Stable release. No new features or API changes.
- Constructor of
BlobCheckpointStorehas been updated to take the storage container details directly rather than an instance of
from_connection_stringconstructor has been added for Blob Storage connection strings.
blobstoragepmaiois now internal, all imports should be directly from
BlobCheckpointStorenow has a
close()function for shutting down an HTTP connection pool, additionally the object can be used in a context manager to manage the connection.
- Added method
list_checkpointswhich list all the checkpoints under given eventhub namespace, eventhub name and consumer group.
This release has trivial internal changes only. No feature changes.
BlobPartitionManagerthat uses Azure Blob Storage Block Blob to store EventProcessor checkpoint data
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