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Alerting - Using ElastAlert 2 with Logs Data Platform

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Stephanie R.
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ElastAlert 2 is an alerting framework originally designed by Yelp. It can detect anomalies, spikes, or other patterns of interest. It is production-ready and is a well-known standard of alerting in the Elasticsearch/OpenSearch ecosystem. Their motto is: "If you can see it in your dashboards, ElastAlert 2 can alert on it." In this document, you will learn how to deploy this component on Logs Data Platform thanks to its compatibility with OpenSearch through aliases and indexes. Logs Data Platform also allows you to host ElastAlert meta-indices on Logs Data Platform.

 

Requirements

 

Preparation

To deploy ElastAlert, you must have data for which you can receive alerts. If you only have Graylog stream, you can use aliases to enable the OpenSearch API on your stream data. Here is how:

  1. Log in to the OVHcloud Control Panel and access your Logs Data Platform service.
  2. In the Alias tab, click on the + Add an alias button.
  3. Choose a name and define a description for your alias.
  4. Save the entry by clicking the Save button.

    operate_LDP_vqe_useOpenSearchAPI02.png

  1. Once the alias has been created, use the more options ... button to the right and select Attach content to the alias option.

    operate_LDP_vqe_useOpenSearchAPI03*.png

  1. Define the Graylog streams you want to associate with your alias.

If you only have indices, you can use them directly in the ElastAlert configuration.

 

Instructions

ElastAlert configuration consists of three steps:

  1. Installing ElastAlert and its metadata indices.
  2. Configuring the main configuration file.
  3. Configuring the alert rules.

Installation

Installing ElastAlert can be done in different ways as described in their documentation. You can either use the docker image or install the Python 3 packages. Check that your Python version is compatible with ElastAlert 2 and that you have met all requirements before attempting installation.

You can either install the latest stable release of ElastAlert 2 using pip...

$ pip install elastalert2

Or you can clone the Jertel ElastAlert repository for the most recent changes:

$ git clone https://github.com/jertel/elastalert2.git

And then install the module:

$ pip install "setuptools>=11.3"
$ python setup.py install

If there is any error about any missing packages, install them manually. For example:

$ pip install setuptools_rust

The next step is to configure ElastAlert meta-indices using the provided tool elastalert-create-index. ElastAlert needs 5 indices to operate:

  • The generic index containing all active alerts.
  • The status index containing the queries run to trigger the alerts.
  • The error index with all the errors encountered.
  • The silence index indicating if a recurring alert should be triggered or silenced.
  • The past index with all the alerts triggered and closed.

The following command will create the indices on Logs Data Platform directly from OpenSearch API.

$ elastalert-create-index --host <ldp-cluster>.logs.ovh.com --port 9200 --username <username> --password <password> --ssl --index <username>-i-<suffix>

You should pay attention to the following points:

  • The <ldp-cluster> must be the one assigned to you (find on the Logs Data Platform Home page in the OVHcloud Control Panel).
  • <username> is the username used to connect to the API or to the Logs Data Platform interfaces (Graylog or OpenSearch Dashboards).
  • <password> is the associated password. You can use tokens in place of the username/password couple for your credentials.
  • The --index is the most important here since you must follow the index naming convention of Logs Data Platform. Use the presented form <username>-i- as a base name for your meta-indices. <suffix> can be personalized to any alphanumeric characters.

This command will prompt you with different questions:

Verify TLS certificates? t/f: t
Enter optional OpenSearch URL prefix (prepends a string to the URL of every request):
Name of existing index to copy? (Default None)
Reading Elastic 8 index mappings:
Reading index mapping 'es_mappings/8/silence.json'
Reading index mapping 'es_mappings/8/elastalert_status.json'
Reading index mapping 'es_mappings/8/elastalert.json'
Reading index mapping 'es_mappings/8/past_elastalert.json'
Reading index mapping 'es_mappings/8/elastalert_error.json'
New index logs-**-*****-i-***** created
Done!

This will then create five indices and place the mapping on them. All you need after is to create the ElastAlert configuration file and some rules.

 

ElastAlert 2 configuration file

Create a configuration directory (for example /opt/elastalert/) and a rule directory before continuing (such as /opt/elastalert/rules). This rule directory will be used in the configuration below.

Here is a sample config.yml file you can use for your configuration directory:

rules_folder: /opt/elastalert/rules
run_every:
  minutes: 5
buffer_time:
  hours: 6
es_host: <ldp-cluster>.logs.ovh.com
es_port: 9200
use_ssl: True
verify_certs: True
es_username: <username>
es_password: <password>
writeback_index: <username>-i-<suffix>
alert_time_limit:
  days: 2

You can find all the available options here.

  • rules_folder is where ElastAlert will load rule configuration files from. It will attempt to load every .yaml file in the folder. Without any valid rules in this folder, ElastAlert will not start.
  • run_every is how often ElastAlert will query OpenSearch.
  • buffer_time is the size of the query window, stretching backward from the time each query is run.
  • es_host is the address of an OpenSearch cluster where ElastAlert will store data about its state, queries run, alerts, and errors. Each rule may also use a different OpenSearch host to query against.
  • es_port is the port corresponding to es_host.
  • use_ssl: whether or not to connect to es_host using TLS. TLS is mandatory in our platform.
  • verify_certs whether or not to verify TLS certificates. Our platform uses certificates validated by most operating systems and browsers.
  • es_username is the username used to connect to OpenSearch APIs.
  • es_password is the password used to connect to OpenSearch APIs. Remember that you can use tokens in place of these credentials.
  • writeback_index is the name of the index in which ElastAlert will store data. Use the same name you used to configure indices with elastalert-create-index.
  • alert_time_limit is the retry window for failed alerts.

 

Rules configuration

In this example, we will create a frequency.yml rule which will send a email if the field user with the value Oles appears more than 3 times in less than 4 hours and use the debug logger debug.

name: Example frequency rule

# (Required)
# Type of alert.
# the frequency rule type alerts when num_events events occur with timeframe time
type: frequency

# (Required)
# Index to search, wildcard supported
index:  <index-or-alias-to-check>

# (Required, frequency specific)
# Alert when this many documents matching the query occur within a timeframe
num_events: 3

# (Required, frequency specific)
# num_events must occur within this amount of time to trigger an alert
timeframe:
  hours: 4

timestamp_field: timestamp
timestamp_type: custom
timestamp_format: '%Y-%m-%d %H:%M:%S.%f'
timestamp_format_expr:  'ts[:23]'
timestamp_to_datetime_format_expr: 'ts[:23]'

# (Required)
# A list of OpenSearch filters used for find events
# These filters are joined with AND and nested in a filtered query
# For more info: https://opensearch.org/docs/latest/opensearch/query-dsl/index/
filter:
- term:
    user: "Oles"

# (Required)
# The alert is used when a match is found
alert:
- "debug"

We won't detail all the parameters since most of them are self-explanatory. However, please pay attention to the index parameter. This index or alias is the one containing the logs or documents you want to be alerted from.

It's also important to customize the timestamp parameters according to the timestamp of your logs or documents. Here we customize a custom timestamp on the timestamp_field timestamp with the format used in the logs pipeline %Y-%m-%d %H:%M:%S.%f. Because this format can have more than three extra numbers, we need to truncate them using the timestamp_format_expr option. Note that Elastalert does not support nanoseconds, this is why the option timestamp_to_datetime_format_expr cuts the timestamp string to 23 characters, so it can be parsed.

 

Launch ElastAlert

To launch ElastAlert, use the following command:

$ elastalert --config config.yml --debug

To test your alert you can use the following curl command sending logs to our OpenSearch endpoint:

$ curl -H 'Content-Type: application/json' -u '<username>:<password>' -XPOST https://<ldp-cluster>.logs.ovh.com:9200/ldp-logs/_doc -d '{ "X-OVH-TOKEN" : "stream-token>" , "test_field" : "OVHcloud" , "user": "Oles", "short_message" : "Hello OpenSearch input", "host" : "OVHcloud_elastalert" }'

If you send this event more than three times, the ElastAlert process will print the triggered alert.

user01@test:~/rules$ elastalert --config config.yml --debug
INFO:elastalert:Note: In debug mode, alerts will be logged to console but NOT actually sent.
To send them but remain verbose, use --verbose instead.
INFO:elastalert:Note: In debug mode, alerts will be logged to console but NOT actually sent.
To send them but remain verbose, use --verbose instead.
INFO:elastalert:1 rules loaded
INFO:elastalert:Starting up
INFO:elastalert:Disabled rules are: []
INFO:elastalert:Sleeping for 299.999899 seconds
INFO:elastalert:Queried rule Example frequency rule from 2024-08-06 04:03 EDT to 2024-08-06 10:03 EDT: 16 / 16 hits
INFO:elastalert:Skipping writing to ES: {'exponent': 0, 'rule_name': 'Example frequency rule', '@timestamp': '2024-08-06T14:03:25.155726Z', 'until': '2024-08-06T14:04:25.155713Z'}
INFO:elastalert:Alert for Example frequency rule at 2024-08-06T13:46:26.335Z:
INFO:elastalert:Example frequency rule

ElastAlert has a lot of integrations for alerting including Email, JIRA, OpsGenie, SNS, HipChat, Slack, MS Teams, PagerDuty, Zabbix, custom commands, and many more.

 

Go further

For more information and tutorials, please see our other Logs Data Platform support guides or explore the guides for other OVHcloud products and services.

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