kafka application endpoint
Project description
A lightweight application for consistent handling of kafka events
This application was developed to be a universal api endpoint for microservices that process kafka events.
Installation
pip install kafka-python-app
Usage
Configure and create application instance.
Configuration parameters:
- app_name [OPTIONAL]: application name.
- bootstrap_servers: list of kafka bootstrap servers addresses 'host:port'.
- producer_config [OPTIONAL]: kafka producer configuration ( see kafka-python documentation).
# Default producer config
producer_config = {
'key_serializer': lambda x: x.encode('utf-8') if x else x,
"value_serializer": lambda x: json.dumps(x).encode('utf-8')
}
- consumer_config [OPTIONAL]: kafka consumer configuration ( see kafka-python documentation).
# Default consumer config
conf = {
'group_id': str(uuid.uuid4()),
'auto_offset_reset': 'earliest',
'enable_auto_commit': False,
'key_deserializer': lambda x: x.decode('utf-8') if x else x,
'value_deserializer': lambda x: json.loads(x.decode('utf-8')),
'session_timeout_ms': 25000
}
- listen_topics: list of subscribed topics.
- message_key_as_event [OPTIONAL]: set to True if using kafka message key as event name.
NOTE When setting message_key_as_event to True, make sure to specify valid key_deserializer in consumer_config.
- message_value_cls [OPTIONAL]: dictionary {"topic_name": dataclass_type} that maps message dataclass type to specific topic. The application uses this mapping to create specified dataclass from kafka message.value.
- middleware_message_cb [OPTIONAL]: if provided, this callback will be executed with raw kafka message argument before calling any handler.
- emit_with_response_options [OPTIONAL]: configuration that supports use of the emit_with_response method
- pipelines_map [OPTIONAL]: Dict[str, MessagePipeline] - provides mapping of a pipelint to event name or "topic.event" combination.
- max_concurrent_tasks [OPTIONAL]: int - number of individual event handlers executed concurrently
- max_concurrent_pipelines [OPTIONAL]: int - number of pipelines executed concurrently
- logger [OPTIONAL]: any logger with standard log methods. If not provided, the standard python logger is used.
from kafka_python_app.app import AppConfig, KafkaApp
# Setup kafka message payload:
class MyMessage(pydantic.BaseModel):
event: str
prop1: str
prop2: int
# This message type is specific for "test_topic3" only.
class MyMessageSpecific(pydantic.BaseModel):
event: str
prop3: bool
prop4: float
# Create application config
config = AppConfig(
app_name='Test application',
bootstrap_servers=['localhost:9092'],
consumer_config={
'group_id': 'test_app_group'
},
listen_topics=['test_topic1', 'test_topic2', 'test_topic3'],
message_value_cls={
'test_topic1': MyMessage,
'test_topic2': MyMessage,
'test_topic3': MyMessageSpecific
}
)
# Create application
app = KafkaApp(config)
Create event handlers using @app.on decorator:
# This handler will handle 'some_event' no matter which topic it comes from
@app.on(event='some_event')
def handle_some_event(message: MyMessage, **kwargs):
print('Handling event: {}..'.format(message.event))
print('prop1: {}\n'.format(message.prop1))
print('prop2: {}\n'.format(message.prop2))
# This handler will handle 'another_event' from 'test_topic2' only.
# Events with this name but coming from another topic will be ignored.
@app.on(event='another_event', topic='test_topic2')
def handle_some_event(message: MyMessage, **kwargs):
print('Handling event: {}..'.format(message.event))
print('prop1: {}\n'.format(message.prop1))
print('prop2: {}\n'.format(message.prop2))
# This handler will handle 'another_event' from 'test_topic3' only.
@app.on(event='another_event', topic='test_topic3')
def handle_some_event(message: MyMessageSpecific, **kwargs):
print('Handling event: {}..'.format(message.event))
print('prop3: {}\n'.format(message.prop3))
print('prop4: {}\n'.format(message.prop4))
NOTE: If topic argument is provided to @app.on decorator, the decorated function is mapped to particular topic.event key that means an event that comes from a topic other than the specified will not be processed. Otherwise, event will be processed no matter which topic it comes from.
Use message pipelines
The @app.on decorator is used to register a single handler for a message. However, now it is possible to pass a message through a sequence of handlers by providing a pipelines_map option into the application config. The pipelines_map is a dictionary of type Dict[str, MessagePipeline].
MessagePipeline class has following properties:
- transactions: List[MessageTransaction]
- logger (optional): any object that has standard logging methods (debug, info, error, etc.)
MessageTransaction has properties:
- fnc: Callable - transaction function that takes message, somehow transforms it and returns it to next transaction in the pipeline. Every transaction function must have a signature: fnc(message, logger, **kwargs) and has to return message of the same type.
NOTE: Transaction function can be sync or async.
- args: Dict - a dictionary of keyword arguments for transaction function.
- pipe_result_options (optional): TransactionPipeWithReturnOptions - configuration to pipe message to another service (kafka app).
TransactionPipeResultOptions class properties:
- pipe_event_name: str - event name that will be sent pipe_to_topic: str - destination topic with_response_options (optional): TransactionPipeWithReturnOptions - this config is used when pipeline needs to wait response from another service before proceeding to next transaction.
TransactionPipeWithReturnOptions class properties:
- response_event_name: str - event name of the response
- response_from_topic: str - topic name that the response should come from
- cache_client: Any - client of any caching service that has methods get and set
get method signature: get(key: str) -> bytes
set method signature: set(name: str, value: bytes, ex: int (record expiration in sec))
- return_event_timeout: int - timeout in seconds for returned event
TransactionPipeResultOptionsCustom class properties:
NOTE: Use this if you need to implement custom logic after transaction function is executed.
- fnc: Callable - function that will be executed after transaction function is finished.
Function fnc signature: fnc(app_id: str, pipeline_name: str, message: Dict, emitter: [kafka app emit metod], message_key_as_event: bool, fnc_pipe_event, fnc_pipe_event_with_response, logger: [any logger supporting basic logging methods], **kwargs)
Function fnc_pipe_event signature: fnc( pipeline_name: str, message: Dict, emitter: [kafka app emit metod], message_key_as_event: bool, options: TransactionPipeResultOptions logger: [any logger supporting basic logging methods], **kwargs)
Function fnc_pipe_event_with_response signature: fnc(app_id: str, pipeline_name: str, message: Dict, emitter: [kafka app emit metod], message_key_as_event: bool, options: TransactionPipeResultOptions logger: [any logger supporting basic logging methods], **kwargs)
- with_response_options: Optional[TransactionPipeWithReturnOptionsMultikey] - these option will be used by kafka app to register caching pipelines. This is the same as TransactionPipeWithReturnOptions buth instead of separate options response_event_name and response_from_topic there is a list of tuples (response_from_topic, response_event_name) called response_event_topic_keys.
Example:
Suppose we receive a string with each message and that string needs to be processed. Let's say we need replace all commas with a custom symbol and then add a number to the end of the string that correspond to the number of some substring occurrences.
from kafka_python_app.app import AppConfig, KafkaApp, MessagePipeline, MessageTransaction
# Define transaction functions
def txn_replace(message: str, symbol: str, logger=None):
return message.replace(',', symbol)
def txn_add_count(message: str, substr: str, logger=None):
return ' '.join([message, message.count(substr)])
# Define a pipeline
pipeline = MessagePipeline(
transactions=[
MessageTransaction(fnc=txn_replace, args={'symbol': '|'}),
MessageTransaction(fnc=txn_add_count, args={'substr': 'foo'})
]
)
# Define a pipelines map
pipelines_map = {'some_event': pipeline}
# Create application config
config = AppConfig(
app_name='Test application',
bootstrap_servers=['localhost:9092'],
consumer_config={
'group_id': 'test_app_group'
},
listen_topics=['test_topic1'],
pipelines_map=pipelines_map
)
# Create application
app = KafkaApp(config)
NOTE: Define pipelines_map keys in a format 'topic.event' in order to restrict pipeline execution to events that come from a certain topic.
Use app.emit() method to send messages to kafka:
from kafka_python_app import ProducerRecord
msg = ProducerRecord(
key='my_message_key',
value='my_payload'
)
app.emit(topic='some_topic', message=msg)
Use app.emit_with_response() method to send messages to kafka and wait for response event:
Specify emit_with_response_options in the application config.
EmitWithResponseOptions class properties:
- topic_event_list: list of tuples (topic_name: str, event_name: str) for returned events. This defines what events and from what topics should be cached as "response" events.
- cache_client: Any - client of any caching service that has methods get and set
get method signature: get(key: str) -> bytes
set method signature: set(name: str, value: bytes, ex: int (record expiration in sec))
- return_event_timeout: int - timeout in seconds for returned event
from kafka_python_app import KafkaApp, AppConfig, \
EmitWithResponseOptions, ProducerRecord,
# Create application config
config = AppConfig(
app_name='Test application',
bootstrap_servers=['localhost:9092'],
consumer_config={
'group_id': 'test_app_group'
},
listen_topics=['test_topic1'],
emit_with_response_options=EmitWithReturnOptions(
event_topic_list=[
("test_topic_2", "response_event_name")
],
cache_client=redis_client,
return_event_timeout=30
),
)
# Create application
app = KafkaApp(config)
msg = ProducerRecord(
value={"event": "test_event_name": "payload": "Hello?"}
)
response = app.emit_with_response(topic='some_topic', message=msg)
Start application:
if __name__ == "__main__":
asyncio.run(app.run())
Use standalone kafka connector
The KafkaConnector class has two factory methods:
- get_producer method returns kafka-python producer.
- get_listener method returns instance of the KafkaListener class that wraps up kafka-python consumer and ** listen()** method that starts consumption loop.
Use ListenerConfig class to create listener configuration:
from kafka_python_app.connector import ListenerConfig
kafka_listener_config = ListenerConfig(
bootstrap_servers=['ip1:port1', 'ip2:port2', ...],
process_message_cb=my_process_message_func,
consumer_config={'group_id': 'test_group'},
topics=['topic1', 'topic2', ...],
logger=my_logger
)
- bootstrap_servers: list of kafka bootstrap servers addresses 'host:port'.
- process_message_cb: a function that will be called on each message.
from kafka.consumer.fetcher import ConsumerRecord
def my_process_message_func(message: ConsumerRecord):
print('Received kafka message: key: {}, value: {}'.format(
message.key,
message.value
))
NOTE: Use async function for process_message_cb in order to process messages concurrently.
- consumer_config [OPTIONAL]: kafka consumer configuration ( see kafka-python documentation).
- topics: list of topics to listen from.
- logger [OPTIONAL]: any logger with standard log methods. If not provided, the standard python logger is used.
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