@Marvin Is it possible to write the logs of each flow run into a separate log file, named by the flow run ID?

Yes, it's possible to write logs of each flow run into a separate log file named by the flow run ID in Prefect 3.x. Prefect provides a logging system that allows you to configure custom logging for your flows and tasks. Here's a concise approach to achieve this: 1. Use Prefect's Logger: Import

get_run_logger

from

prefect.logging

. This logger is aware of the current flow or task run context, which includes the flow run ID. 2. Customize the Logger: You can customize the logging configuration to direct logs to a file. You would typically use Python's logging module to configure a

FileHandler

that writes logs to a file named after the flow run ID. Here's a skeleton of how you might set it up:

python
from prefect import flow
from prefect.logging import get_run_logger
import logging

@flow
def my_flow():
    logger = get_run_logger()
    # Customize logger to write to a file named by the flow run ID
    flow_run_id = logger.context.run_id
    handler = logging.FileHandler(f"{flow_run_id}.log")
    logger.addHandler(handler)
    
    # Your flow logic here
    <http://logger.info|logger.info>("This is a log message.")

my_flow()

- Documentation: For more details on configuring logging in Prefect, you can refer to the Prefect Logging Documentation. This setup should allow you to have separate log files for each flow run, named by the flow run ID.

@Marvin How can I specify the path, where the log file should be written to?

To specify the path where the log file should be written, you can configure the logging setup using Python's logging module. You can set the

FileHandler

to write to a specific directory. Here's how you can do it: 1. Set the File Path: When you create the

FileHandler

, specify the full path where you want the log file to be stored. Here's an example:

python
from prefect import flow
from prefect.logging import get_run_logger
import logging
import os

@flow
def my_flow():
    logger = get_run_logger()
    flow_run_id = logger.context.run_id
    log_directory = "/path/to/log/directory"  # Specify your desired directory
    os.makedirs(log_directory, exist_ok=True)  # Ensure the directory exists
    log_file_path = os.path.join(log_directory, f"{flow_run_id}.log")
    
    handler = logging.FileHandler(log_file_path)
    logger.addHandler(handler)
    
    # Your flow logic here
    <http://logger.info|logger.info>("This is a log message.")

my_flow()

- Ensure Directory Exists: The

os.makedirs(log_directory, exist_ok=True)

line ensures that the directory exists before writing the log file. - Documentation: For more detailed logging configurations, refer to the Prefect Logging Documentation. This approach allows you to direct the log files to a specific directory of your choosing.

@Marvin Unfortunately, I get an error: AttributeError: 'PrefectLogAdapter' object has no attribute 'addHandler'

The error you're encountering is because the

get_run_logger()

function in Prefect returns a

PrefectLogAdapter

, which does not have an

addHandler

method. To customize logging, you should configure the root logger or a specific logger using a configuration file or directly within your code. Here's how you can configure logging to write to a specific file path: 1. Configure the Root Logger: Use Python's logging module to configure the root logger, which will propagate logs from Prefect's logger. 2. Set Up a Logging Configuration: You can set up a logging configuration using a

logging.yaml

file or directly in your script. Here's an example of configuring the logging directly in your script:

python
import logging
import os
from prefect import flow
from prefect.logging import get_run_logger

# Configure the root logger
log_directory = "/path/to/log/directory"
os.makedirs(log_directory, exist_ok=True)
log_file_path = os.path.join(log_directory, "prefect_flow.log")

logging.basicConfig(
    level=<http://logging.INFO|logging.INFO>,
    format='%(asctime)s - %(name)s - %(levelname)s - %(message)s',
    handlers=[
        logging.FileHandler(log_file_path),
        logging.StreamHandler()
    ]
)

@flow
def my_flow():
    logger = get_run_logger()
    <http://logger.info|logger.info>("This is a log message.")

my_flow()

- Documentation: For more detailed configurations, you can refer to the Prefect Logging Documentation. This setup will log all messages to the specified file and the console, ensuring that your flow logs are captured as needed.

@Marvin Can the code be modified in such a way, that each flow run writes its logs to a log file named by its flow run ID?

To ensure each flow run writes its logs to a separate file named by the flow run ID, you'll need to dynamically configure the logging within the flow. Here's how you can achieve this: 1. Configure Logging Inside the Flow: Use the

logging

module to set up a

FileHandler

with a filename based on the flow run ID. Here's a complete example:

python
import logging
import os
from prefect import flow
from prefect.logging import get_run_logger

@flow
def my_flow():
    # Get the Prefect logger
    logger = get_run_logger()
    
    # Extract the flow run ID from the logger context
    flow_run_id = logger.context.run_id
    
    # Define the log directory and file path
    log_directory = "/path/to/log/directory"
    os.makedirs(log_directory, exist_ok=True)
    log_file_path = os.path.join(log_directory, f"{flow_run_id}.log")
    
    # Set up a file handler for the specific flow run
    file_handler = logging.FileHandler(log_file_path)
    formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
    file_handler.setFormatter(formatter)
    
    # Get the root logger and add the file handler
    root_logger = logging.getLogger()
    root_logger.addHandler(file_handler)
    
    # Your flow logic here
    <http://logger.info|logger.info>("This is a log message.")

    # Remove the file handler after the flow run to avoid duplicate logs
    root_logger.removeHandler(file_handler)

my_flow()

- Ensure Directory Exists: The

os.makedirs(log_directory, exist_ok=True)

line ensures that the directory exists before writing the log file. - Dynamic File Naming: Each flow run will have its logs written to a file named after its run ID. - Cleanup: The file handler is removed at the end of the flow to prevent duplicate logs in subsequent runs. This setup effectively isolates logs for each flow run, ensuring clarity and ease of debugging.

@Marvin Can I use this code in multiple flows, that are executed at the same time, or could there be interferences?

Yes, you can use this code in multiple flows executed simultaneously without interference. Each flow run will independently configure its logging, writing to a unique log file named by its flow run ID. This ensures that logs are isolated per flow run. Here's why this setup works well concurrently: 1. Unique Log Files: Each flow run writes to its own log file, named using its unique flow run ID. This prevents any overlap in log writing. 2. Independent Logging Configuration: The logging configuration, including the file handler, is set up and torn down within each flow execution. This localizes the logging setup to the flow's execution context. 3. Thread Safety: Python's logging module is designed to be thread-safe, meaning that concurrent writes to different files by different threads (or processes) will not interfere with each other. This approach ensures that each flow run's logs are kept separate, even when multiple flows are executed simultaneously.

@Marvin How can the code be configured, so that all log messages that can be seen in the UI, are logged in the files?

To ensure that all log messages visible in the Prefect UI are also logged in your files, you can configure the logging to capture all relevant logs, including those from other libraries used in your flows. Here's how you can do it: 1. Include Logs from Other Libraries: Use the

PREFECT_LOGGING_EXTRA_LOGGERS

setting to capture logs from additional libraries used in your flows. 2. Configure Logging to File: Set up your logging to write to a file, ensuring that all captured logs are directed there. Here's an example of how to configure this:

python
import logging
import os
from prefect import flow
from prefect.logging import get_run_logger

# Configure additional loggers if needed
os.environ["PREFECT_LOGGING_EXTRA_LOGGERS"] = "dask,scipy"  # Example libraries

@flow
def my_flow():
    # Get the Prefect logger
    logger = get_run_logger()
    
    # Extract the flow run ID from the logger context
    flow_run_id = logger.context.run_id
    
    # Define the log directory and file path
    log_directory = "/path/to/log/directory"
    os.makedirs(log_directory, exist_ok=True)
    log_file_path = os.path.join(log_directory, f"{flow_run_id}.log")
    
    # Set up a file handler for the specific flow run
    file_handler = logging.FileHandler(log_file_path)
    formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
    file_handler.setFormatter(formatter)
    
    # Get the root logger and add the file handler
    root_logger = logging.getLogger()
    root_logger.addHandler(file_handler)
    
    # Your flow logic here
    <http://logger.info|logger.info>("This is a log message.")

    # Remove the file handler after the flow run to avoid duplicate logs
    root_logger.removeHandler(file_handler)

my_flow()

- Environment Variable: The

PREFECT_LOGGING_EXTRA_LOGGERS

environment variable allows you to specify additional loggers to include, ensuring that logs from other libraries are captured. - Documentation: For more details on logging configuration, refer to the Prefect Logging Documentation. This setup will ensure that all logs, including those seen in the UI, are also written to your specified log files.

@Marvin I mean Prefect log messages such as:

Worker 'ProcessWorker [...] submitting flow run [...]

or

Completed submission of flow run [...]

To capture Prefect's internal log messages, such as worker submissions and flow run completions, you need to ensure that the root logger is configured to capture logs from Prefect's internal loggers. Prefect's log messages are typically emitted at the INFO level, so setting up your logging configuration to capture INFO level messages should suffice. Here's how you can configure your logging to capture these messages: 1. Configure the Root Logger: Ensure that the root logger is set to capture INFO level logs and higher. 2. Direct Logs to a File: Use a

FileHandler

to write these logs to a file named by the flow run ID. Here's an example:

python
import logging
import os
from prefect import flow
from prefect.logging import get_run_logger

@flow
def my_flow():
    # Get the Prefect logger
    logger = get_run_logger()
    
    # Extract the flow run ID from the logger context
    flow_run_id = logger.context.run_id
    
    # Define the log directory and file path
    log_directory = "/path/to/log/directory"
    os.makedirs(log_directory, exist_ok=True)
    log_file_path = os.path.join(log_directory, f"{flow_run_id}.log")
    
    # Configure the root logger
    root_logger = logging.getLogger()
    root_logger.setLevel(<http://logging.INFO|logging.INFO>)  # Capture INFO level logs and above
    
    # Set up a file handler for the specific flow run
    file_handler = logging.FileHandler(log_file_path)
    formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
    file_handler.setFormatter(formatter)
    root_logger.addHandler(file_handler)
    
    # Your flow logic here
    <http://logger.info|logger.info>("This is a log message.")
    
    # Remove the file handler after the flow run to avoid duplicate logs
    root_logger.removeHandler(file_handler)

my_flow()

- Root Logger Configuration: By setting the root logger's level to INFO, you ensure that all logs at this level and above, including Prefect's internal logs, are captured. - FileHandler: The file handler directs these logs to a file specific to each flow run. This setup should ensure that you capture all relevant Prefect log messages in your log files.

@Marvin At the moment, only the following log message is in the file: 2025-03-15 223013,257 - prefect.flow_runs - INFO - This is a log message.

To ensure that all Prefect internal log messages, such as worker submissions and flow run completions, are captured in your log files, you need to ensure that the logging configuration captures logs from Prefect's internal loggers. Here's how you can adjust your configuration to achieve this: 1. Set the Root Logger Level: Ensure that the root logger is set to capture DEBUG level logs, which will include all logs from Prefect. 2. Capture All Prefect Logs: Prefect uses several loggers internally, so make sure these are included in your logging configuration. Here's how you can configure your logging setup:

python
import logging
import os
from prefect import flow
from prefect.logging import get_run_logger

@flow
def my_flow():
    # Get the Prefect logger
    logger = get_run_logger()
    
    # Extract the flow run ID from the logger context
    flow_run_id = logger.context.run_id
    
    # Define the log directory and file path
    log_directory = "/path/to/log/directory"
    os.makedirs(log_directory, exist_ok=True)
    log_file_path = os.path.join(log_directory, f"{flow_run_id}.log")
    
    # Set up the root logger to capture all logs
    root_logger = logging.getLogger()
    root_logger.setLevel(logging.DEBUG)  # Capture all logs, including DEBUG level
    
    # Set up a file handler for the specific flow run
    file_handler = logging.FileHandler(log_file_path)
    formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
    file_handler.setFormatter(formatter)
    root_logger.addHandler(file_handler)
    
    # Your flow logic here
    <http://logger.info|logger.info>("This is a log message.")
    
    # Remove the file handler after the flow run to avoid duplicate logs
    root_logger.removeHandler(file_handler)

my_flow()

- DEBUG Level: By setting the root logger to DEBUG, you ensure that all logs, including those typically sent to the UI, are captured. - FileHandler: This configuration ensures that all logs are directed to a file specific to each flow run. This setup should capture all relevant logs, including Prefect's internal operational messages, in your log files.