Logging using elasticsearch-py

Question

I would like to log my python script that uses elasticsearch-py. In particular, I want to have three logs:

General log: log INFO and above both to the stdout and to a file.
ES log: only ES related messages only to a file.
ES tracing log: Extended ES logging (curl queries and their output for instance) only to a file.

Here is what I have so far:

import logging
import logging.handlers

es_logger = logging.getLogger('elasticsearch')
es_logger.setLevel(logging.INFO)
es_logger_handler=logging.handlers.RotatingFileHandler('top-camps-base.log',
                                                          maxBytes=0.5*10**9,
                                                          backupCount=3)
es_logger.addHandler(es_logger_handler)

es_tracer = logging.getLogger('elasticsearch.trace')
es_tracer.setLevel(logging.DEBUG)
es_tracer_handler=logging.handlers.RotatingFileHandler('top-camps-full.log',
                                                       maxBytes=0.5*10**9,
                                                       backupCount=3)
es_tracer.addHandler(es_tracer_handler)

logger = logging.getLogger('mainLog')
logger.setLevel(logging.DEBUG)
# create file handler
fileHandler = logging.handlers.RotatingFileHandler('top-camps.log',
                                                   maxBytes=10**6,
                                                   backupCount=3)
fileHandler.setLevel(logging.INFO)
# create console handler
consoleHandler = logging.StreamHandler()
consoleHandler.setLevel(logging.INFO)
# create formatter and add it to the handlers
formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
consoleHandler.setFormatter(formatter)
fileHandler.setFormatter(formatter)
# add the handlers to logger
logger.addHandler(consoleHandler)
logger.addHandler(fileHandler)

My problem is that INFO messages of es_logger are displayed also on the terminal. As a matter of fact the log messages are saved to the right files!

If I remover the part related to logger, then the ES logging works fine, i.e. only saved to the corresponding files. But then I don't have the other part.... What is it that I'm doing wrong with the last part of the settings?

Edit

Possible hint: In the sources of elasticsearch-py there's a logger named logger. Could it be that it conflicts with mine? I tried to change the name of logger to main_logger in the lines above but it didn't help.

Possible hint 2: If I replace logger = logging.getLogger('mainLog') with logger = logging.getLogger(), then the format of the output to the console of es_logger changes and becomes identical to the one defined in the snippet.

Anton · Accepted Answer · 2014-12-15 14:54:40Z

I think you are being hit by the somewhat confusing logger hierarchy propagation. Everything that is logged in "elasticsearch.trace" that passes the loglevel of that logger, will propagate first to the "elasticsearch" logger and then to the root ("") logger. Note that once the message passes the loglevel of the "elasticsearch.trace" logger, the loglevels of the parents ("elasticsearch" and root) are not checked, but all messages will be sent to the handlers. (The handlers themselves have log levels that do apply.)

Consider the following example that illustrates the issue, and a possible solution:

import logging

# The following line will basicConfig() the root handler
logging.info('DUMMY - NOT SEEN')
ll = logging.getLogger('foo')
ll.setLevel('DEBUG')
ll.addHandler(logging.StreamHandler())
ll.debug('msg1')
ll.propagate = False
ll.debug('msg2')

Output:

msg1
DEBUG:foo:msg1
msg2

You see that "msg1" is logged both by the "foo" logger, and its parent, the root logger (as "DEBUG:foo:msg1"). Then, when propagation is turned off ll.propagate = False before "msg2", the root logger no longer logs it. Now, if you were to comment out the first line (logging.info("DUMMY..."), then the behavior would change so that the root logger line would not be shown. This is because the logging module top level functions info(), debug() etc. configure the root logger with a handler when no handler has yet been defined. That is also why you see different behavior in your example when you modify the root handler by doing logger = logging.getLogger().

I can't see in your code that you would be doing anything to the root logger, but as you see, a stray logging.info() or the like in your code or library code would cause a handler to be added.

So, to answer your question, I would set logger.propagate = False to the loggers where it makes sense for you and where you want propagation, check that the log level of the handlers themselves are as you want them.

Here is an attempt:

es_logger = logging.getLogger('elasticsearch')
es_logger.propagate = False
es_logger.setLevel(logging.INFO)
es_logger_handler=logging.handlers.RotatingFileHandler('top-camps-base.log',
                                                      maxBytes=0.5*10**9,
                                                      backupCount=3)
es_logger.addHandler(es_logger_handler)

es_tracer = logging.getLogger('elasticsearch.trace')
es_tracer.propagate = False
es_tracer.setLevel(logging.DEBUG)
es_tracer_handler=logging.handlers.RotatingFileHandler('top-camps-full.log',
                                                   maxBytes=0.5*10**9,
                                                   backupCount=3)
es_tracer.addHandler(es_tracer_handler)

logger = logging.getLogger('mainLog')
logger.propagate = False
logger.setLevel(logging.DEBUG)
# create file handler
fileHandler = logging.handlers.RotatingFileHandler('top-camps.log',
                                               maxBytes=10**6,
                                               backupCount=3)
fileHandler.setLevel(logging.INFO)
# create console handler
consoleHandler = logging.StreamHandler()
consoleHandler.setLevel(logging.INFO)
# create formatter and add it to the handlers
formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(message)s')
consoleHandler.setFormatter(formatter)
fileHandler.setFormatter(formatter)
# add the handlers to logger
logger.addHandler(consoleHandler)
logger.addHandler(fileHandler)

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