Reading and Writing Application Logs


When a request is sent to your app, a request log is automatically written by App Engine. During the handling of the request, your app can also write application logs. In this page, you'll learn how to write application logs from your application, how to read both application and request logs programmatically using the Logs API, how to view logging in the Google Cloud Platform Console, and how to understand the request log data that App Engine writes during the request.

Request logs vs application logs

There are two categories of log data: request logs and application logs. A request log is automatically written by App Engine for each request handled by your app, and contains information such as the project ID, HTTP version, and so forth. For a complete list of available properties for request logs, see RequestLog. See also the request log table for descriptions of the request log fields.

Each request log contains a list of application logs (AppLog) associated with that request, returned in the RequestLog.app_logs property. Each app log contains the time the log was written, the log message, and the log level.

Writing application logs

You may find it useful to read the documentation for the standard Python logging module at

The Python logging module allows a developer to log 5 levels of severity. :

  • Debug
  • Info
  • Warning
  • Error
  • Critical

The following example shows how to use the different logging levels:

import logging

import webapp2

class MainPage(webapp2.RequestHandler):
    def get(self):
        logging.debug('This is a debug message')'This is an info message')
        logging.warning('This is a warning message')
        logging.error('This is an error message')
        logging.critical('This is a critical message')

            raise ValueError('This is a sample value error.')
        except ValueError:
            logging.exception('A example exception log.')

        self.response.out.write('Logging example.')

app = webapp2.WSGIApplication([
    ('/', MainPage)
], debug=True)

Reading logs via API

The general process of getting logs using the Logs API is as follows:

  1. Use fetch() to return an iterator for the request logs.
  2. In each iteration, process each RequestLog as desired.
  3. Optionally, use RequestLog.app_logs to get the list of related AppLogs.
  4. If you retrieved the app logs list, for each AppLogLine, process the AppLog property data as desired.

Sample code

The following sample displays 5 request logs at at time, along with their application logs. It lets you cycle through each set of 10 logs using a Next link.

import base64
import datetime
from itertools import islice
from textwrap import dedent
import time

from google.appengine.api.logservice import logservice
import webapp2

def get_logs(offset=None):
    # Logs are read backwards from the given end time. This specifies to read
    # all logs up until now.
    end_time = time.time()

    logs = logservice.fetch(

    return logs

def format_log_entry(entry):
    # Format any application logs that happened during this request.
    logs = []
    for log in entry.app_logs:
        date = datetime.datetime.fromtimestamp(
            log.time).strftime('%D %T UTC')
        logs.append('Date: {}, Message: {}'.format(
            date, log.message))

    # Format the request log and include the application logs.
    date = datetime.datetime.fromtimestamp(
        entry.end_time).strftime('%D %T UTC')

    output = dedent("""
        Date: {}
        IP: {}
        Method: {}
        Resource: {}
    """.format(date, entry.ip, entry.method, entry.resource))

    output += '\n'.join(logs)

    return output

class MainPage(webapp2.RequestHandler):
    def get(self):
        offset = self.request.get('offset', None)

        if offset:
            offset = base64.urlsafe_b64decode(str(offset))

        # Get the logs given the specified offset.
        logs = get_logs(offset=offset)

        # Output the first 10 logs.
        log = None
        for log in islice(logs, 10):

            offset = log.offset

        if not log:
            self.response.write('No log entries found.')

        # Add a link to view more log entries.
        elif offset:
                '<a href="/?offset={}"">More</a>'.format(

app = webapp2.WSGIApplication([
    ('/', MainPage)
], debug=True)

In the sample, notice that the GET handler expects to be re-invoked by the user clicking on the Next link, and so it extracts the offset param, if present. That offset is used in the subsequent re-invocation of logservice.fetch() to "page through" each group of 5 request logs. There is nothing special about the number 5; it can be anything you want.

Log URL format in the Google Cloud Platform Console

See the following sample URL for an example of the log URL format in the GCP Console:

Reading logs in the console

To view logs using the Log Viewer:

  1. In the GCP Console, go to the logs for your project.

  2. Use the desired filter to retrieve the logs you want to see. You can filter by various combinations of time, log level, module, and log filter label or regular expression.

    Notice that labels are regular expressions for filtering the logs by logging fields. Valid labels include the following:

    • day
    • month
    • year
    • hour
    • minute
    • second
    • tzone
    • remotehost
    • identd_user
    • user
    • status
    • bytes
    • referrer
    • useragent
    • method
    • path
    • querystring
    • protocol
    • request_id

    For example, path:/foo.* useragent:.*Chrome.* gets logs for all requests to a path starting with /foo that were issued from a Chrome browser.

A typical App Engine log contains data in the Apache combined log format, along with some special App Engine fields, as shown in the following sample log: - test [27/Jun/2014:09:11:47 -0700] "GET / HTTP/1.1" 200 414
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/35.0.1916.153 Safari/537.36"
"" ms=195 cpu_ms=42 cpm_usd=0.000046
loading_request=1 instance=00c61b117cfeb66f973d7df1b7f4ae1f064d app_engine_release=1.9.60

Understanding request log fields

The following table lists the fields in order of occurrence along with a description:

Field Order Field Name Always Present? Description
1 Client address Yes Client IP address. Example:
2 RFC1413 identity No RFC1413 identity of the client. This is nearly always the character -
3 User No Present only if the app uses the Users API and the user is logged in. This value is the "nickname" portion of the Google Account, for example, if the Google Account is, the nickname that is logged in this field is test.
4 Timestamp Yes Request timestamp. Example: [27/Jun/2014:09:11:47 -0700]
5 Request querystring Yes First line of the request, containing method, path, and HTTP version. Example: GET / HTTP/1.1
6 HTTP Status Code Yes Returned HTTP status code. Example: 200
7 Response size Yes Response size in bytes. Example: 414
8 Referrer path No If there is no referrer, the log contains no path, but only -. Example referrer path: "".
9 User-agent Yes Identifies the browser and operating system to the web server. Example: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/35.0.1916.153 Safari/537.36
10 Hostname Yes The hostname used by the client to connect to the App Engine application. Example : (
11 Wallclock time Yes Total clock time in milliseconds spent by App Engine on the request. This time duration does not include time spent between the client and the server running the instance of your application. Example: ms=195.
12 CPU milliseconds Yes CPU milliseconds required to fulfill the request. This is the number of milliseconds spent by the CPU actually executing your application code, expressed in terms of a baseline 1.2 GHz Intel x86 CPU. If the CPU actually used is faster than the baseline, the CPU milliseconds can be larger than the actual clock time defined above. Example: cpu_ms=42
13 Exit code No Only present if the instance shut down after getting the request. In the format exit_code=XXX where XXX is a 3 digit number corresponding to the reason the instance shut down. The exit codes are not documented since they are primarily intended to help Google spot and fix issues.
14 Estimated cost Yes DEPRECATED. Estimated cost of 1000 requests just like this one, in USD. Example: cpm_usd=0.000046
15 Queue name No The name of the task queue used. Only present if request used a task queue. Example: queue_name=default
16 Task name No The name of the task executed in the task queue for this request. Only present if the request resulted in the queuing of a task. Example: task_name=7287390692361099748
17 Pending queue No Only present if a request spent some time in a pending queue. If there are many of these in your logs and/or the values are high, it might be an indication that you need more instances to serve your traffic. Example: pending_ms=195
18 Loading request No Only present if the request is a loading request. This means an instance had to be started up. Ideally, your instances should be up and healthy for as long as possible, serving large numbers of requests before being recycled and needing to be started again. Which means you shouldn't see too many of these in your logs. Example: loading_request=1.
19 Instance Yes Unique identifier for the instance that handles the request. Example: instance=00c61b117cfeb66f973d7df1b7f4ae1f064d
20 Version Yes The current App Engine release version used in production App Engine: 1.9.60

Quotas and limits

Your application is affected by the following logs-related quotas:

  • Logs data retrieved via the Logs API.
  • Log ingestion allotment and retention.

Quota for data retrieved

The first 100 megabytes of logs data retrieved per day via the Logs API calls are free. After this amount is exceeded, no further Logs API calls will succeed unless billing is enabled for your app. If billing is enabled for your app, data in excess of 100 megabytes results in charges of $0.12/GB.

Logs ingestion allotment

Logging for App Engine apps is provided by Stackdriver. By default, logs are stored for an application free of charge for up to 7 days and 5GB. Logs older than the maximum retention time are deleted, and attempts to store above the free ingestion limit of 5 gigabytes will result in an error. You can update to the Premium Tier for greater storage capacity and retention length. See Stackdriver pricing for more information on logging rates and limits. If you want to retain your logs for longer than what Stackdriver allows, you can export logs to Google Cloud Storage, Google BigQuery, or Google Cloud Pub/Sub.

The development server and Logs API

By default, logs are stored in memory only in the development server and are accessible if you wish to test the Logs API feature. If you wish to persist logs from the development server to disk at the default location /tmp/dev_appserver.logs, supply the --persist_logs command line option as follows: --persist_logs your-app-directory

If you wish to persist the logs from the development server to disk at a location of your own choosing, supply the desired path and filename to the --logs_path command line option as follows: --logs_path=your-path/your-logfile-name your-app-directory

Send feedback about...

App Engine standard environment for Python