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ASGI Correlation ID middleware
Middleware for reading or generating correlation IDs for each incoming request. Correlation IDs can then be added to your
logs, making it simple to retrieve all logs generated from a single HTTP request.
When the middleware detects a correlation ID HTTP header in an incoming request, the ID is stored. If no header is
found, a correlation ID is generated for the request instead.
The middleware checks for the X-Request-ID
header by default, but can be set to any key.
X-Correlation-ID
is also pretty commonly used.
Example
Once logging is configured, your output will go from this:
INFO ... project.views This is an info log
WARNING ... project.models This is a warning log
INFO ... project.views This is an info log
INFO ... project.views This is an info log
WARNING ... project.models This is a warning log
WARNING ... project.models This is a warning log
to this:
INFO ... [773fa6885] project.views This is an info log
WARNING ... [773fa6885] project.models This is a warning log
INFO ... [0d1c3919e] project.views This is an info log
INFO ... [99d44111e] project.views This is an info log
WARNING ... [0d1c3919e] project.models This is a warning log
WARNING ... [99d44111e] project.models This is a warning log
Now we're actually able to see which logs are related.
Installation
pip install asgi-correlation-id
Setup
To set up the package, you need to add the middleware and configure logging.
Adding the middleware
The middleware can be added like this:
from fastapi import FastAPI
from asgi_correlation_id import CorrelationIdMiddleware
app = FastAPI()
app.add_middleware(CorrelationIdMiddleware)
or any other way your framework allows.
For Starlette apps, just substitute FastAPI
with Starlette
in all examples.
Configure logging
This section assumes you have already started configuring logging in your project. If this is not the case, check out
the section on setting up logging from scratch instead.
To set up logging of the correlation ID, you simply have to add the log-filter the package provides.
If your current log-config looked like this:
LOGGING = {
'version': 1,
'disable_existing_loggers': False,
'formatters': {
'web': {
'class': 'logging.Formatter',
'datefmt': '%H:%M:%S',
'format': '%(levelname)s ... %(name)s %(message)s',
},
},
'handlers': {
'web': {
'class': 'logging.StreamHandler',
'formatter': 'web',
},
},
'loggers': {
'my_project': {
'handlers': ['web'],
'level': 'DEBUG',
'propagate': True,
},
},
}
You simply have to add the filter, like this:
LOGGING = {
'version': 1,
'disable_existing_loggers': False,
+ 'filters': {
+ 'correlation_id': {
+ '()': 'asgi_correlation_id.CorrelationIdFilter',
+ 'uuid_length': 32,
+ 'default_value': '-',
+ },
+ },
'formatters': {
'web': {
'class': 'logging.Formatter',
'datefmt': '%H:%M:%S',
+ 'format': '%(levelname)s ... [%(correlation_id)s] %(name)s %(message)s',
},
},
'handlers': {
'web': {
'class': 'logging.StreamHandler',
+ 'filters': ['correlation_id'],
'formatter': 'web',
},
},
'loggers': {
'my_project': {
'handlers': ['web'],
'level': 'DEBUG',
'propagate': True,
},
},
}
If you're using a json log-formatter, just add correlation-id: %(correlation_id)s
to your list of properties.
Middleware configuration
The middleware can be configured in a few ways, but there are no required arguments.
app.add_middleware(
CorrelationIdMiddleware,
header_name='X-Request-ID',
update_request_header=True,
generator=lambda: uuid4().hex,
validator=is_valid_uuid4,
transformer=lambda a: a,
)
Configurable middleware arguments include:
header_name
- Type:
str
- Default:
X-Request-ID
- Description: The header name decides which HTTP header value to read correlation IDs from.
X-Request-ID
and
X-Correlation-ID
are common choices.
update_request_header
- Type:
bool
- Default:
True
- Description: Whether to update incoming request's header value with the generated correlation ID. This is to support
use cases where it's relied on the presence of the request header (like various tracing middlewares).
generator
- Type:
Callable[[], str]
- Default:
lambda: uuid4().hex
- Description: The generator function is responsible for generating new correlation IDs when no ID is received from an
incoming request's headers. We use UUIDs by default, but if you prefer, you could use libraries
like nanoid or your own custom function.
validator
- Type:
Callable[[str], bool]
- Default:
is_valid_uuid4
(
found here) - Description: The validator function is used when reading incoming HTTP header values. By default, we discard non-UUID
formatted header values, to enforce correlation ID uniqueness. If you prefer to allow any header value, you can set
this setting to
None
, or pass your own validator.
transformer
- Type:
Callable[[str], str]
- Default:
lambda a: a
- Description: Most users won't need a transformer, and by default we do nothing.
The argument was added for cases where users might want to alter incoming or generated ID values in some way. It
provides a mechanism for transforming an incoming ID in a way you see fit. See the middleware code for more context.
CORS
If you are using cross-origin resource sharing (CORS), e.g.
you are making requests to an API from a frontend JavaScript code served from a different origin, you have to ensure
two things:
- permit correlation ID header in the incoming requests' HTTP headers so the value can be reused by the middleware,
- add the correlation ID header to the allowlist in responses' HTTP headers so it can be accessed by the browser.
This can be best accomplished by using a dedicated middleware for your framework of choice. Here are some examples.
Starlette
Docs: https://www.starlette.io/middleware/#corsmiddleware
from starlette.applications import Starlette
from starlette.middleware import Middleware
from starlette.middleware.cors import CORSMiddleware
middleware = [
Middleware(
CORSMiddleware,
allow_origins=['*'],
allow_methods=['*'],
allow_headers=['X-Requested-With', 'X-Request-ID'],
expose_headers=['X-Request-ID']
)
]
app = Starlette(..., middleware=middleware)
FastAPI
Docs: https://fastapi.tiangolo.com/tutorial/cors/
from app.main import app
from fastapi.middleware.cors import CORSMiddleware
app.add_middleware(
CORSMiddleware,
allow_origins=['*'],
allow_methods=['*'],
allow_headers=['X-Requested-With', 'X-Request-ID'],
expose_headers=['X-Request-ID']
)
For more details on the topic, refer to the CORS protocol.
Exception handling
By default, the X-Request-ID
response header will be included in all responses from the server, except in the case
of unhandled server errors. If you wish to include request IDs in the case of a 500
error you can add a custom
exception handler.
Here are some simple examples to help you get started. See each framework's documentation for more info.
Starlette
Docs: https://www.starlette.io/exceptions/
from starlette.requests import Request
from starlette.responses import PlainTextResponse
from starlette.applications import Starlette
from asgi_correlation_id import correlation_id
async def custom_exception_handler(request: Request, exc: Exception) -> PlainTextResponse:
return PlainTextResponse(
"Internal Server Error",
status_code=500,
headers={'X-Request-ID': correlation_id.get() or ""}
)
app = Starlette(
...,
exception_handlers={500: custom_exception_handler}
)
FastAPI
Docs: https://fastapi.tiangolo.com/tutorial/handling-errors/
from app.main import app
from fastapi import HTTPException, Request
from fastapi.exception_handlers import http_exception_handler
from fastapi.responses import JSONResponse
from asgi_correlation_id import correlation_id
@app.exception_handler(Exception)
async def unhandled_exception_handler(request: Request, exc: Exception) -> JSONResponse:
return await http_exception_handler(
request,
HTTPException(
500,
'Internal server error',
headers={'X-Request-ID': correlation_id.get() or ""}
))
If you are using CORS, you also have to include the Access-Control-Allow-Origin
and Access-Control-Expose-Headers
headers in the error response. For more details, see the CORS section above.
Setting up logging from scratch
If your project does not have logging configured, this section will explain how to get started. If you want even more
details, take a look
at this blogpost
.
The Python docs explain there are a few configuration functions
you may use for simpler setup. For this example we will use dictConfig
, because that's what, e.g., Django users should
find most familiar, but the different configuration methods are interchangable, so if you want to use another method,
just browse the python docs and change the configuration method as you please.
The benefit of dictConfig
is that it lets you specify your entire logging configuration in a single data structure,
and it lets you add conditional logic to it. The following example shows how to set up both console and JSON logging:
from logging.config import dictConfig
from app.core.config import settings
def configure_logging() -> None:
dictConfig(
{
'version': 1,
'disable_existing_loggers': False,
'filters': {
'correlation_id': {
'()': 'asgi_correlation_id.CorrelationIdFilter',
'uuid_length': 8 if not settings.ENVIRONMENT == 'local' else 32,
'default_value': '-',
},
},
'formatters': {
'console': {
'class': 'logging.Formatter',
'datefmt': '%H:%M:%S',
'format': '%(levelname)s:\t\b%(asctime)s %(name)s:%(lineno)d [%(correlation_id)s] %(message)s',
},
},
'handlers': {
'console': {
'class': 'logging.StreamHandler',
'filters': ['correlation_id'],
'formatter': 'console',
},
},
'loggers': {
'app': {'handlers': ['console'], 'level': 'DEBUG', 'propagate': True},
'databases': {'handlers': ['console'], 'level': 'WARNING'},
'httpx': {'handlers': ['console'], 'level': 'INFO'},
'asgi_correlation_id': {'handlers': ['console'], 'level': 'WARNING'},
},
}
)
With the logging configuration defined within a function like this, all you have to do is make sure to run the function
on startup somehow, and logging should work for you. You can do this any way you'd like, but passing it to
the FastAPI.on_startup
list of callables is a good starting point.
Integration with structlog
structlog is a Python library that enables structured logging.
It is trivial to configure with asgi_correlation_id
:
import logging
from typing import Any
import structlog
from asgi_correlation_id import correlation_id
def add_correlation(
logger: logging.Logger, method_name: str, event_dict: dict[str, Any]
) -> dict[str, Any]:
"""Add request id to log message."""
if request_id := correlation_id.get():
event_dict["request_id"] = request_id
return event_dict
structlog.configure(
processors=[
add_correlation,
structlog.stdlib.filter_by_level,
structlog.stdlib.add_logger_name,
structlog.stdlib.add_log_level,
structlog.processors.TimeStamper(fmt="%Y-%m-%d %H:%M.%S"),
structlog.processors.StackInfoRenderer(),
structlog.processors.format_exc_info,
structlog.processors.JSONRenderer(),
],
wrapper_class=structlog.stdlib.BoundLogger,
logger_factory=structlog.stdlib.LoggerFactory(),
cache_logger_on_first_use=True,
)
Integration with SAQ
If you're using saq, you
can easily transfer request IDs from the web server to your
workers by using the event hooks provided by the library:
from uuid import uuid4
from asgi_correlation_id import correlation_id
from saq import Job, Queue
CID_TRANSFER_KEY = 'correlation_id'
async def before_enqueue(job: Job) -> None:
"""
Transfer the correlation ID from the current context to the worker.
This might be called from a web server or a worker process.
"""
job.meta[CID_TRANSFER_KEY] = correlation_id.get() or uuid4()
async def before_process(ctx: dict) -> None:
"""
Load correlation ID from the enqueueing process to this one.
"""
correlation_id.set(ctx['job'].meta.get(CID_TRANSFER_KEY, uuid4()))
async def after_process(ctx: dict) -> None:
"""
Reset correlation ID for this process.
"""
correlation_id.set(None)
queue = Queue(...)
queue.register_before_enqueue(before_enqueue)
priority_settings = {
...,
'queue': queue,
'before_process': before_process,
'after_process': after_process,
}
To add a correlation ID to your hypercorn logs, you'll need to add a log filter and change the log formatting. Here's an example of how to configure hypercorn, if you're running a FastAPI app:
import logging
import os
from fastapi import APIRouter, FastAPI
from hypercorn.config import Config
from hypercorn.asyncio import serve
import asgi_correlation_id
import asyncio
import hypercorn
def configure_logging():
console_handler = logging.StreamHandler()
console_handler.addFilter(asgi_correlation_id.CorrelationIdFilter())
logging.basicConfig(
handlers=[console_handler],
level="INFO",
format="%(levelname)s log [%(correlation_id)s] %(name)s %(message)s")
app = FastAPI(on_startup=[configure_logging])
app.add_middleware(asgi_correlation_id.CorrelationIdMiddleware)
router = APIRouter()
@router.get("/test")
async def test_get():
print("toto")
logger = logging.getLogger()
logger.info("test_get")
app.include_router(router)
if __name__ == "__main__":
logConfig = {
"handlers": {
"hypercorn.access": {
"formatter": "hypercorn.access",
"level": "INFO",
"class": "logging.StreamHandler",
"stream": "ext://sys.stdout",
"filters": [
asgi_correlation_id.CorrelationIdFilter()
],
}},
"formatters": {
"hypercorn.access": {
"format": "%(message)s %(correlation_id)s",
}
},
"loggers": {
"hypercorn.access": {
"handlers": [
"hypercorn.access"
],
"level": "INFO",
},
},
"version": 1
}
config = Config()
config.accesslog = "-"
config.logconfig_dict = logConfig
asyncio.run(serve(app, config))
# run it
$ python3 test.py
# test it:
$ curl http://localhost:8080/test
# log on stdout:
INFO log [7e7ccfff352a428991920d1da2502674] root test_get
127.0.0.1:34754 - - [14/Dec/2023:10:34:08 +0100] "GET /test 1.1" 200 4 "-" "curl/7.76.1" 7e7ccfff352a428991920d1da2502674
Integration with Uvicorn
To add a correlation ID to your uvicorn logs, you'll need to add a log filter and change the log formatting. Here's an example of how to configure uvicorn, if you're running a FastAPI app:
import logging
import os
import asgi_correlation_id
import uvicorn
from fastapi import APIRouter, FastAPI
from uvicorn.config import LOGGING_CONFIG
def configure_logging():
console_handler = logging.StreamHandler()
console_handler.addFilter(asgi_correlation_id.CorrelationIdFilter())
logging.basicConfig(
handlers=[console_handler],
level="INFO",
format="%(levelname)s log [%(correlation_id)s] %(name)s %(message)s")
app = FastAPI(on_startup=[configure_logging])
app.add_middleware(asgi_correlation_id.CorrelationIdMiddleware)
router = APIRouter()
@router.get("/test")
async def test_get():
logger = logging.getLogger()
logger.info("test_get")
app.include_router(router)
if __name__ == "__main__":
LOGGING_CONFIG["handlers"]["access"]["filters"] = [asgi_correlation_id.CorrelationIdFilter()]
LOGGING_CONFIG["formatters"]["access"]["fmt"] = "%(levelname)s access [%(correlation_id)s] %(name)s %(message)s"
uvicorn.run("test:app", port=8080, log_level=os.environ.get("LOGLEVEL", "DEBUG").lower())
# run it
python test.py
# test it
curl http://localhost:8080/test
# log on stdout
INFO log [16b61d57f9ff4a85ac80f5cd406e0aa2] root test_get
INFO access [16b61d57f9ff4a85ac80f5cd406e0aa2] uvicorn.access 127.0.0.1:24810 - "GET /test HTTP/1.1" 200
Extensions
In addition to the middleware, we've added a couple of extensions for third-party packages.
Sentry
If your project has sentry-sdk
installed, correlation IDs will automatically be added to Sentry events as a transaction_id
.
See
this blogpost
for a little bit of detail. The transaction ID is displayed in the event detail view in Sentry and is just an easy way
to connect logs to a Sentry event.
Celery
Note: If you're using the celery integration, install the package with pip install asgi-correlation-id[celery]
For Celery user's there's one primary issue: workers run as completely separate processes, so correlation IDs are lost
when spawning background tasks from requests.
However, with some Celery signal magic, we can actually transfer correlation IDs to worker processes, like this:
@before_task_publish.connect()
def transfer_correlation_id(headers) -> None:
headers[header_key] = correlation_id.get()
@task_prerun.connect()
def load_correlation_id(task) -> None:
id_value = task.request.get(header_key)
correlation_id.set(id_value)
To configure correlation ID transfer, simply import and run the setup function the package provides:
from asgi_correlation_id.extensions.celery import load_correlation_ids
load_correlation_ids()
Taking it one step further - Adding Celery tracing IDs
In addition to transferring request IDs to Celery workers, we've added one more log filter for improving tracing in
celery processes. This is completely separate from correlation ID functionality, but is something we use ourselves, so
keep in the package with the rest of the signals.
The log filter adds an ID, celery_current_id
for each worker process, and an ID, celery_parent_id
for the process
that spawned it.
Here's a quick summary of outputs from different scenarios:
Scenario | Correlation ID | Celery Current ID | Celery Parent ID |
---|
Request | ✅ | | |
Request -> Worker | ✅ | ✅ | |
Request -> Worker -> Another worker | ✅ | ✅ | ✅ |
Beat -> Worker | ✅* | ✅ | |
Beat -> Worker -> Worker | ✅* | ✅ | ✅ |
*When we're in a process spawned separately from an HTTP request, a correlation ID is still spawned for the first
process in the chain, and passed down. You can think of the correlation ID as an origin ID, while the combination of
current and parent-ids as a way of linking the chain.
To add the current and parent IDs, just alter your celery.py
to this:
+ from asgi_correlation_id.extensions.celery import load_correlation_ids, load_celery_current_and_parent_ids
load_correlation_ids()
+ load_celery_current_and_parent_ids()
If you wish to correlate celery task IDs through the IDs found in your broker (i.e., the celery task_id
), use the use_internal_celery_task_id
argument on load_celery_current_and_parent_ids
from asgi_correlation_id.extensions.celery import load_correlation_ids, load_celery_current_and_parent_ids
load_correlation_ids()
+ load_celery_current_and_parent_ids(use_internal_celery_task_id=True)
Note: load_celery_current_and_parent_ids
will ignore the generator
argument when use_internal_celery_task_id
is set to True
To set up the additional log filters, update your log config like this:
LOGGING = {
'version': 1,
'disable_existing_loggers': False,
'filters': {
'correlation_id': {
+ '()': 'asgi_correlation_id.CorrelationIdFilter',
+ 'uuid_length': 32,
+ 'default_value': '-',
+ },
+ 'celery_tracing': {
+ '()': 'asgi_correlation_id.CeleryTracingIdsFilter',
+ 'uuid_length': 32,
+ 'default_value': '-',
+ },
},
'formatters': {
'web': {
'class': 'logging.Formatter',
'datefmt': '%H:%M:%S',
'format': '%(levelname)s ... [%(correlation_id)s] %(name)s %(message)s',
},
+ 'celery': {
+ 'class': 'logging.Formatter',
+ 'datefmt': '%H:%M:%S',
+ 'format': '%(levelname)s ... [%(correlation_id)s] [%(celery_parent_id)s-%(celery_current_id)s] %(name)s %(message)s',
+ },
},
'handlers': {
'web': {
'class': 'logging.StreamHandler',
'filters': ['correlation_id'],
'formatter': 'web',
},
+ 'celery': {
+ 'class': 'logging.StreamHandler',
+ 'filters': ['correlation_id', 'celery_tracing'],
+ 'formatter': 'celery',
+ },
},
'loggers': {
'my_project': {
+ 'handlers': ['celery' if any('celery' in i for i in sys.argv) else 'web'],
'level': 'DEBUG',
'propagate': True,
},
},
}
With these IDs configured you should be able to:
- correlate all logs from a single origin, and
- piece together the order each log was run, and which process spawned which
Example
With everything configured, assuming you have a set of tasks like this:
@celery.task()
def debug_task() -> None:
logger.info('Debug task 1')
second_debug_task.delay()
second_debug_task.delay()
@celery.task()
def second_debug_task() -> None:
logger.info('Debug task 2')
third_debug_task.delay()
fourth_debug_task.delay()
@celery.task()
def third_debug_task() -> None:
logger.info('Debug task 3')
fourth_debug_task.delay()
fourth_debug_task.delay()
@celery.task()
def fourth_debug_task() -> None:
logger.info('Debug task 4')
your logs could look something like this:
correlation-id current-id
| parent-id |
| | |
INFO [3b162382e1] [ - ] [93ddf3639c] project.tasks - Debug task 1
INFO [3b162382e1] [93ddf3639c] [24046ab022] project.tasks - Debug task 2
INFO [3b162382e1] [93ddf3639c] [cb5595a417] project.tasks - Debug task 2
INFO [3b162382e1] [24046ab022] [08f5428a66] project.tasks - Debug task 3
INFO [3b162382e1] [24046ab022] [32f40041c6] project.tasks - Debug task 4
INFO [3b162382e1] [cb5595a417] [1c75a4ed2c] project.tasks - Debug task 3
INFO [3b162382e1] [08f5428a66] [578ad2d141] project.tasks - Debug task 4
INFO [3b162382e1] [cb5595a417] [21b2ef77ae] project.tasks - Debug task 4
INFO [3b162382e1] [08f5428a66] [8cad7fc4d7] project.tasks - Debug task 4
INFO [3b162382e1] [1c75a4ed2c] [72a43319f0] project.tasks - Debug task 4
INFO [3b162382e1] [1c75a4ed2c] [ec3cf4113e] project.tasks - Debug task 4