Follow Elasticsearch continuously

Overview

elasticsearch_follow is library helping to query Elasticsearch continuously.

It needs https://github.com/elastic/elasticsearch-py as a dependency.

elasticsearch_follow acts as a wrapper for elasticsearch-py and handles various use-cases, like following logs by polling elasticsearch continuously and fetching loglines via a generator. It is possible to easily fetch lines surrounding a given logline.

How to poll Elasticsearch continuously

The polling logic is implemented in the class ElasticsearchFollow, which needs an Elasircsearch object from elasticsearch-py. The class Follower takes an ElasticsearchFollow-object and has a method to create a generator which yields loglines until all elements of a query have been returned. After this a new generator has to be created and used.

How to fetch log-lines from Elasticsearch

To just fetch loglines, one can use ElasticsearchFetch which has a search_surrounding. This returns a list of lists, where each list contains the queried loglines and the lines before and after as requested by the parameters num_before and num_after.

Installation

You can install the elasticsearch package with pip:

pip install elasticsearch_follow

See also: https://pypi.org/project/elasticsearch-follow/

Example usage

This package introduces the command line tool es_tail which can be used for following logs written to Elasticsearch and directly fetching log lines by a query. It is possible to configure the output via an format string.

# Follow the logs written to the indexes starting with logstash.
# Print the fieds @timestamp and message
es_tail -c "http://localhost:9200" tail --index "logstash*" -f "{@timestamp} {message}" 


# Fetch all logs in the last hour with the field loglevel contains ERROR and fetch the two lines before and after.
# Print the fieds @timestamp and message
es_tail -c "http://localhost:9200" fetch --index "logstash" -f "{@timestamp} {message}" --query loglevel:ERROR -A 2 -B 2 -F "now-1h" 


# It is also possible to print nested fields
es_tail -c "http://localhost:9200" fetch --index "logstash" -f "{@timestamp} {message} {kv[field]} {kv[nested][field]}" -F "now-1h" 

The command line options can also be given via environment variables by using the prefix ES_TAIL. For example

export ES_TAIL_USERNAME='username'
export ES_TAIL_PASSWORD='password'
es_tail -c http://localhost:9200 tail

Example usage of the library

from elasticsearch import Elasticsearch
from elasticsearch_follow import ElasticsearchFollow, Follower

es = Elasticsearch()
es_follow = ElasticsearchFollow(elasticsearch=es)

# The Follower is used to get a generator which yields new 
# elements until it runs out. time_delta give the number of
# seconds to look into the past.
follower = Follower(elasticsearch_follow=es_follow, index='some-index', time_delta=60)

while True:
    entries = follower.generator()
    for entry in entries:
        print(entry)
    time.sleep(0.1)