Easy publish and subscribe to events with python and Kafka.
Project description
kafkaesk
This project is meant to help facilitate easily publishing and subscribing to events with python and Kafka.
Guiding principal:
- simple http, language agnostic contracts built on top of kafka.
Alternatives:
- pure aiokafka: can be complex to scale correctly
- guillotina_kafka: complex, tied to guillotina
- faust: requires additional data layers, not language agnostic
- confluent kafka + avro: close but ends up being like grpc. compilation for languages. No asyncio.
(consider this python project as syntatic sugar around these ideas)
Publish
using pydantic but can be done with pure json
import kafkaesk
from pydantic import BaseModel
app = kafkaesk.Application()
@app.schema("Content", version=1, retention=24 * 60 * 60)
class ContentMessage(BaseModel):
foo: str
async def foobar():
# ...
# doing something in an async func
await app.publish("content.edited.Resource", data=ContentMessage(foo="bar"))
Subscribe
import kafkaesk
from pydantic import BaseModel
app = kafkaesk.Application()
@app.schema("Content", version=1, retention=24 * 60 * 60)
class ContentMessage(BaseModel):
foo: str
@app.subscribe('content.*', 'group_id')
async def get_messages(data: ContentMessage):
print(f"{data.foo}")
Retry
Clients may configure a subscriber with different retry behaviors depending on what exception was raised by the subscription callback. Subscriptions accept a dictionary of Exception types and kafkaesk.retry.RetryHandlers as an argument when registered.
The default RetryHandler is kafkaesk.retry.Raise. The Raise handler will cause the exception to be re-raised and terminate the subscriber.
import kafkaesk
from pydantic import BaseModel
app = kafkaesk.Application()
@app.schema("Content", version=1, retention=24 * 60 * 60)
class ContentMessage(BaseModel):
foo: str
@app.subscribe("content.*", "group_id", retry_handlers={Exception: kafkaesk.retry.Forward("dlx.content")})
async def get_messages(data: ContentMessage):
raise Exception("UnhandledException")
Avoiding global object
If you do not want to have global application configuration, you can lazily configure the application and register schemas/subscribers separately.
import kafkaesk
from pydantic import BaseModel
router = kafkaesk.Router()
@router.schema("Content", version=1, retention=24 * 60 * 60)
class ContentMessage(BaseModel):
foo: str
@router.subscribe('content.*')
async def get_messages(data: ContentMessage):
print(f"{data.foo}")
if __name__ == '__main__':
app = kafkaesk.Application()
app.mount(router)
kafkaesk.run(app)
Optional consumer injected parameters:
- schema: str
- record: aiokafka.structs.ConsumerRecord
- app: kafkaesk.app.Application
- subscriber: kafkaesk.app.SubscriptionConsumer
Depending on the type annotation for the first parameter, you will get different data injected:
async def get_messages(data: ContentMessage): parses pydantic schemaasync def get_messages(data: bytes): give raw byte dataasync def get_messages(record: aiokafka.structs.ConsumerRecord): give kafka record objectasync def get_messages(data): raw json data in message
manual commit
To accomplish a manual commit strategy yourself:
app = kafkaesk.Application(auto_commit=False)
@app.subscribe('content.*')
async def get_messages(data: ContentMessage, subscriber):
print(f"{data.foo}")
await subscriber.commit()
kafkaesk contract
This is just a library around using kafka. Kafka itself does not enforce these concepts.
- every message must provide a json schema
- messages produced will be validated against json schema
- each topic will have only one schema
- a single schema can be used for multiple topics
- consumed message schema validation is up to the consumer
- messages will be consumed at least once. Considering this, your handling should be idempotent
message format
{
"schema": "schema_name:1",
"data": { ... }
}
Worker
kafkaesk mymodule:app --kafka-servers=localhost:9092
Options:
- --kafka-servers: comma separated list of kafka servers
- --kafka-settings: json encoded options to be passed to https://aiokafka.readthedocs.io/en/stable/api.html#aiokafkaconsumer-class
- --topic-prefix: prefix to use for topics
- --replication-factor: what replication factor topics should be created with. Defaults to min(number of servers, 3).
Application.publish
- stream_id: str: name of stream to send data to
- data: class that inherits from pydantic.BaseModel
- key: Optional[bytes]: key for message if it needs one
Application.subscribe
- stream_id: str: fnmatch pattern of streams to subscribe to
- group: Optional[str]: consumer group id to use. Will use name of function if not provided
Application.schema
- id: str: id of the schema to store
- version: Optional[int]: version of schema to store
- streams: Optional[List[str]]: if streams are known ahead of time, we can pre-create them before we push data
- retention: Optional[int]: retention policy in seconds
Application.configure
- kafka_servers: Optional[List[str]]: kafka servers to connect to
- topic_prefix: Optional[str]: topic name prefix to subscribe to
- kafka_settings: Optional[Dict[str, Any]]: additional aiokafka settings to pass in
- replication_factor: Optional[int]: what replication factor topics should be created with. Defaults to min(number of servers, 3).
- kafka_api_version: str: default
auto - auto_commit: bool: default
True - auto_commit_interval_ms: int: default
5000
Dev
poetry install
Run tests:
docker-compose up
KAFKA=localhost:9092 poetry run pytest tests
Extensions
Logging
This extension includes classes to extend python's logging framework to publish structured log messages to a kafka topic. This extension is made up of three main components: an extended logging.LogRecord and some custom logging.Handlers.
See logger.py in examples directory.
Log Record
kafkaesk.ext.logging.record.factory is a function that will return kafkaesk.ext.logging.record.PydanticLogRecord objects. The factory() function scans through any args passed to a logger and checks each item to determine if it is a subclass of pydantid.BaseModel. If it is a base model instance and model._is_log_model evaluates to True the model will be removed from args and added to record._pydantic_data. After that factory() will use logging's existing logic to finish creating the log record.
Handler
This extensions ships with two handlers capable of handling kafkaesk.ext.logging.handler.PydanticLogModel classes: kafakesk.ext.logging.handler.PydanticStreamHandler and kafkaesk.ext.logging.handler.PydanticKafkaeskHandler.
The stream handler is a very small wrapper around logging.StreamHandler, the signature is the same, the only difference is that the handler will attempt to convert any pydantic models it receives to a human readable log message.
The kafkaesk handler has a few more bits going on in the background. The handler has two required inputs, a kafkaesk.app.Application instance and a stream name. Once initialized any logs emitted by the handler will be saved into an internal queue. There is a worker task that handles pulling logs from the queue and writing those logs to the specified topic.
Naming things
It's hard and "kafka" is already a fun name. Hopefully this library isn't literally "kafkaesque" for you.
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