Library for adding request context to log records
Project description
Python Logging Context
pylogctx is a library for enriching logs records with context fields. Typical usage is for adding some request_id to all logs in order to make troubleshooting more comfortable. This context is shared by all app using logging, transparently.
Usage
You have two option to send the context to the log system: inject context as extra fields in records or append context to the each message.
Using filter
This method allow to pass fields to JSON formatters, log servers, etc. or use the extra fields in format string.
LOGGING = {
'version': 1,
'formatters': {
'extra': {
'format': '%(levelname)s %(rid)s %(name)s %(message)s',
},
},
'filters': {
'context_filter': {
'()': 'pylogctx.AddContextFilter',
'default': {'rid': None},
}
},
'handlers': {
'console': {
'class': 'logging.StreamHandler',
'filters': ['context_filter'],
},
},
'root': {
'handlers': ['console'],
'level': 'DEBUG',
},
}
Note three things:
%(rid) in format string is for logging rid (for request_id) from our context;
pylogctx.AddContextFilter - filter which converts keys from context dict to attributes of LogRecord;
'default': {'rid': None} - some of our log events could be without context for example logs emitted on worker start. All these logs will not be recorded due to the lack of ‘rid’ attribute (in our example) on LogRecord instance. To fix this we provide default value for ‘rid’.
Using formatter
If you do not want to bother with custom log format and default context values for a filter - you can use pylogctx.AddContextFormatter.
LOGGING = {
'version': 1,
'formatters': {
'append': {
'()': 'pylogctx.AddContextFormatter'
'format': '%(levelname)s %(name)s %(message)s'
},
},
'handlers': {
'console': {
'class': 'logging.StreamHandler',
'formatter': 'append',
},
},
'root': {
'handlers': ['console'],
'level': 'DEBUG',
},
}
As you can see in this case we doesn’t add any context related fields to a log format string. This is because pylogctx.AddContextFormatter will append all context information to every log.
Feeding the context
The context class is just a thread local dict. It is used as local registry to inject shared fields in log records. Here is a full example:
from pylogctx.log import context as log_context
log_context.push(userId=user.pk)
# code, log, etc.
for article in blog.articles:
with log_context(articleId=article.pk):
# code, log, ...
# code, log, etc.
log_context.pop('userId')
Automatic feeding with middleware
A middleware is provided to inject extra fields in context. It will also clear the context after each requests.
MIDDLEWARE_CLASSES = [
'pylogctx.django.ExtractRequestContextMiddleware',
# rest middlewares...
]
PYLOGCTX_REQUEST_EXTRACTOR = lambda request: {'rid': request.GET.getlist('rid')}
Here PYLOGCTX_REQUEST_EXTRACTOR is a callable which takes django.http.request.HttpRequest and returns dictionary with extracted context.
Note: ExtractRequestContextMiddleware will fail with exception if no PYLOGCTX_REQUEST_EXTRACTOR specified.
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