This article is the third of a three-piece how to.
To create alerts for our ELK setup, we can use different methods.
The one I will show you is based on ElastAlert from Yelp.
Let's install ElastAlert (no port is available, so I will install it manually in a virtualenv).
We need to be root (and use bash - for the virtualenv)
Create and use a virtualenv
virtualenv /usr/local/elastalert source /usr/local/elastalert/bin/activate mkdir -p /usr/local/elastalert/etc
Download and install the repo
mkdir /tmp/elastalert cd /tmp/elastalert git clone https://github.com/Yelp/elastalert.git cd elastalert python setup.py build pip install setuptools --upgrade python setup.py install pip install -r requirements.txt # the first time it will (probably) fail due to an error related to argparse pip install -r requirements.txt
Create the elastalert config file in /usr/local/elastalert/etc/config.yml
rules_folder: /usr/local/elastalert/etc/rules # The unit can be anything from weeks to seconds run_every: minutes: 1 # ElastAlert will buffer results from the most recent # period of time, in case some log sources are not in real time buffer_time: minutes: 15 # The elasticsearch hostname for metadata writeback # Note that every rule can have it's own elasticsearch host es_host: 127.0.0.1 # The elasticsearch port es_port: 9100 # Optional URL prefix for elasticsearch #es_url_prefix: elasticsearch # Connect with SSL to elasticsearch use_ssl: False # The index on es_host which is used for metadata storage # This can be a unmapped index, but it is recommended that you run # elastalert-create-index to set a mapping writeback_index: elastalert_status # If an alert fails for some reason, ElastAlert will retry # sending the alert until this time period has elapsed alert_time_limit: days: 2
Create the rules directory
mkdir -p /usr/local/elastalert/etc/rules
Create an alert (frequency based) that will send an email if more than 9 events will happen in 1 hour with status: 404 and type: nginx
name: Large Number of 404 Responses es_host: 127.0.0.1 es_port: 9100 index: logstash-* filter: - term: - status: 404 - term: - type: nginx type: frequency num_events: 10 timeframe: hours: 1 alert: - "email" email: - "[email protected]"
Create an index for metadata storage
(elastalert)[[email protected] /usr/local/elastalert]$ ./bin/elastalert-create-index Enter elasticsearch host: 127.0.0.1 Enter elasticsearch port: 9100 Use SSL? t/f: f Enter optional basic-auth username: Enter optional basic-auth password: Enter optional Elasticsearch URL prefix: New index name? (Default elastalert_status) Name of existing index to copy? (Default None) New index elastalert_status created Done!
Test our rule
(elastalert)[[email protected] /usr/local/elastalert]# ./bin/elastalert-test-rule etc/rules/frequency_nginx_404.yaml [...]
Launch ElastAlert (in a tmux session, maybe?)
(elastalert)[[email protected] /usr/local/elastalert]$ ./bin/elastalert --config etc/config.yml --debug INFO:elastalert:Starting up INFO:elastalert:Queried rule Large Number of 404 Responses from 2016-02-16 17:22 CET to 2016-02-16 17:37 CET: 9 hits [...] INFO:elastalert:Ran Large Number of 404 Responses from 2016-02-16 17:22 CET to 2016-02-16 17:37 CET: 9 query hits, 0 matches, 0 alerts sent
INFO:elastalert:Sleeping for 59 seconds INFO:elastalert:Queried rule Large Number of 404 Responses from 2016-02-16 17:23 CET to 2016-02-16 17:38 CET: 10 hits [...] INFO:elastalert:Alert for Large Number of 404 Responses at 2016-02-16T16:38:00.680Z: INFO:elastalert:Large Number of 404 Responses At least 10 events occurred between 2016-02-16 16:38 CET and 2016-02-16 17:38 CET @timestamp: 2016-02-16T16:38:00.680Z @version: 1 _id: AVLq8hzNIkvyITAb373u _index: logstash-2016.02.16 _type: nginx agent: "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2564.109 Safari/537.36" bytes: 564 file: /var/log/nginx/nginx.access.log host: [ "blog.gufi.org" ] message: xxx.xxx.xxx.xxx - blog.gufi.org [16/Feb/2016:17:37:57 +0100] "GET /test/foo/bar HTTP/1.1" 404 564 "-" "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2564.109 Safari/537.36" "184.108.40.206" [-] "-" "-" "0.000" offset: 1853436 remote_addr: xxx.xxx.xxx.xxx request_httpversion: 1.1 request_time: 0.000 request_url: /test/foo/bar request_verb: GET status: 404 time_local: 16/Feb/2016:17:37:57 +0100 type: nginx upstream_addr: - xforwardedfor: "xxx.xxx.xxx.xxx"
Once removed the --debug parameter, we will start receiving e-mails. (yay!)
Few words to answer the question 'Ok, so how can this be useful to me/my company/my fiancee?'
Many of us, sysadmins (or gods), have used Nagios and its derivatives (Zabbix/Icinga) for years but it's time now to say Nagios goodbye (and thanks for all the fish).
Tools like ELK or OpenTSDB (or InfluxDB/KairosDB) and Bosun/Prometheus have been created to give us a new generation of more suitable tools in environments that become bigger and bigger: I know, to create and manage an ELK stack (or a OpenTSDB/Grafana/Bosun stack) requires more effort than to manage a Nagios box, but it's an overhead you will soon get used to (and probably you already have an hadoop/hbase installation to manage, right?).
In this case, having an in house tool to parse your application logs will allow you:
- to blame developers if something goes wrong (just in case you need further reasons to)
- to not give them access to any production machines (yes, they will ask to, anyway)
- to be able to search all your logs at once (like grepping on a syslog-ng basedir with improved superpowers) or with a better semantics (i.e. spotting trends)
- to create dashboards (for your management, you know...) or alerts (because you need a good reason to skip that boring meeting, right?)
ELK engineers suggest to use ELK not only for DEBUG/ERROR messages, but also for the application ones: this will add a great value to your logs and, once again, the world will be a safer place thanks to you, bro.
There were no screenshots in this article, so that's a potato for you here