Running ElastAlert 2

ElastAlert 2 can easily be run as a Docker container or directly on your machine as a Python package. If you are not interested in modifying the internals of ElastAlert 2, the Docker container is recommended for ease of use.

Configuration flags

However you choose to run ElastAlert 2, the ElastAlert 2 process is started by invoking python elastalert/elastalert.py.

This command accepts several configuration flags:

--config will specify the configuration file to use. The default is config.yaml. See here to understand what behaviour can be configured in this file.

--debug will run ElastAlert 2 in debug mode. This will increase the logging verboseness, change all alerts to DebugAlerter, which prints alerts and suppresses their normal action, and skips writing search and alert metadata back to Elasticsearch. Not compatible with –verbose.

--end <timestamp> will force ElastAlert 2 to stop querying after the given time, instead of the default, querying to the present time. This really only makes sense when running standalone. The timestamp is formatted as YYYY-MM-DDTHH:MM:SS (UTC) or with timezone YYYY-MM-DDTHH:MM:SS-XX:00 (UTC-XX).

--es_debug will enable logging for all queries made to Elasticsearch.

--es_debug_trace <trace.log> will enable logging curl commands for all queries made to Elasticsearch to the specified log file. --es_debug_trace is passed through to elasticsearch.py which logs localhost:9200 instead of the actual es_host:es_port.

--pin_rules will stop ElastAlert 2 from loading, reloading or removing rules based on changes to their config files.

--prometheus_port exposes ElastAlert 2 Prometheus metrics on the specified port. Prometheus metrics disabled by default.

--rule <rule.yaml> will only run the given rule. The rule file may be a complete file path or a filename in rules_folder or its subdirectories.

--silence <unit>=<number> will silence the alerts for a given rule for a period of time. The rule must be specified using --rule. <unit> is one of days, weeks, hours, minutes or seconds. <number> is an integer. For example, --rule noisy_rule.yaml --silence hours=4 will stop noisy_rule from generating any alerts for 4 hours.

--silence_qk_value <value will silence the rule only for the given query key value. This parameter is intended to be used with the --rule parameter.

--start <timestamp> will force ElastAlert 2 to begin querying from the given time, instead of the default, querying from the present. The timestamp should be ISO8601, e.g. YYYY-MM-DDTHH:MM:SS (UTC) or with timezone YYYY-MM-DDTHH:MM:SS-08:00 (PST). Note that if querying over a large date range, no alerts will be sent until that rule has finished querying over the entire time period. To force querying from the current time, use “NOW”.

--verbose will increase the logging verboseness, which allows you to see information about the state of queries. Not compatible with –debug.

As a Docker container

If you’re interested in a pre-built Docker image check out the elastalert2 project on Docker Hub.

Be aware that the latest tag of the image represents the latest commit into the master branch. If you prefer to upgrade more slowly you will need utilize a versioned tag, such as 2.2.2 instead, or 2 if you are comfortable with always using the latest released version of ElastAlert 2.

A properly configured config.yaml file must be mounted into the container during startup of the container. Use the example file provided as a template, and once saved locally to a file such as /tmp/elastalert.yaml, run the container as follows:

docker run -d -v /tmp/elastalert.yaml:/opt/elastalert/config.yaml jertel/elastalert2

To build the image locally run the following command:

docker build . -t elastalert2

As a Kubernetes deployment

The Docker container for ElastAlert 2 can be used directly as a Kubernetes deployment, but for convenience, a Helm chart is also available. See the instructions provided on Github for more information on how to install, configure, and run the chart.

As a Python package

Requirements

  • Elasticsearch

  • ISO8601 or Unix timestamped data

  • Python 3.9

  • pip

  • Packages on Ubuntu 21.x: build-essential python3-pip python3.9 python3.9-dev libffi-dev libssl-dev

If you want to install python 3.9 on CentOS, please install python 3.9 from the source code after installing ‘Development Tools’.

Downloading and Configuring

You can either install the latest released version of ElastAlert 2 using pip:

$ pip install elastalert2

or you can clone the ElastAlert2 repository for the most recent changes:

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

Install the module:

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

Next, open up examples/config.yaml.example. In it, you will find several configuration options. ElastAlert 2 may be run without changing any of these settings.

rules_folder is where ElastAlert 2 will load rule configuration files from. It will attempt to load every .yaml file in the folder. Without any valid rules, ElastAlert 2 will not start. ElastAlert 2 will also load new rules, stop running missing rules, and restart modified rules as the files in this folder change. For this tutorial, we will use the examples/rules folder.

run_every is how often ElastAlert 2 will query Elasticsearch.

buffer_time is the size of the query window, stretching backwards from the time each query is run. This value is ignored for rules where use_count_query or use_terms_query is set to true.

es_host is the address of an Elasticsearch cluster where ElastAlert 2 will store data about its state, queries run, alerts, and errors. Each rule may also use a different Elasticsearch host to query against.

es_port is the port corresponding to es_host.

use_ssl: Optional; whether or not to connect to es_host using TLS; set to True or False.

verify_certs: Optional; whether or not to verify TLS certificates; set to True or False. The default is True

ssl_show_warn: Optional; suppress TLS and certificate related warnings; set to True or False. The default is True.

client_cert: Optional; path to a PEM certificate to use as the client certificate

client_key: Optional; path to a private key file to use as the client key

ca_certs: Optional; path to a CA cert bundle to use to verify SSL connections

es_username: Optional; basic-auth username for connecting to es_host.

es_password: Optional; basic-auth password for connecting to es_host.

es_bearer: Optional; bearer token authorization for connecting to es_host. If bearer token is specified, login and password are ignored.

es_url_prefix: Optional; URL prefix for the Elasticsearch endpoint.

statsd_instance_tag: Optional; prefix for statsd metrics.

statsd_host: Optional; statsd host.

es_send_get_body_as: Optional; Method for querying Elasticsearch - GET, POST or source. The default is GET

writeback_index is the name of the index in which ElastAlert 2 will store data. We will create this index later.

alert_time_limit is the retry window for failed alerts.

Save the file as config.yaml

Setting Up Elasticsearch

ElastAlert 2 saves information and metadata about its queries and its alerts back to Elasticsearch. This is useful for auditing, debugging, and it allows ElastAlert 2 to restart and resume exactly where it left off. This is not required for ElastAlert 2 to run, but highly recommended.

First, we need to create an index for ElastAlert 2 to write to by running elastalert-create-index and following the instructions. Note that this manual step is only needed by users that run ElastAlert 2 directly on the host, whereas container users will automatically see these indexes created on startup.:

$ elastalert-create-index
New index name (Default elastalert_status)
Name of existing index to copy (Default None)
New index elastalert_status created
Done!

For information about what data will go here, see ElastAlert 2 Metadata Index.

Creating a Rule

Each rule defines a query to perform, parameters on what triggers a match, and a list of alerts to fire for each match. We are going to use examples/rules/example_frequency.yaml as a template:

# From examples/rules/example_frequency.yaml
es_host: elasticsearch.example.com
es_port: 14900
name: Example rule
type: frequency
index: logstash-*
num_events: 50
timeframe:
  hours: 4
filter:
- term:
    some_field: "some_value"
alert:
- "email"
email:
- "elastalert@example.com"

es_host and es_port should point to the Elasticsearch cluster we want to query.

name is the unique name for this rule. ElastAlert 2 will not start if two rules share the same name.

type: Each rule has a different type which may take different parameters. The frequency type means “Alert when more than num_events occur within timeframe.” For information other types, see Rule types.

index: The name of the index(es) to query. If you are using Logstash, by default the indexes will match "logstash-*".

num_events: This parameter is specific to frequency type and is the threshold for when an alert is triggered.

timeframe is the time period in which num_events must occur.

filter is a list of Elasticsearch filters that are used to filter results. Here we have a single term filter for documents with some_field matching some_value. See Writing Filters For Rules for more information. If no filters are desired, it should be specified as an empty list: filter: []

alert is a list of alerts to run on each match. For more information on alert types, see Alerts. The email alert requires an SMTP server for sending mail. By default, it will attempt to use localhost. This can be changed with the smtp_host option.

email is a list of addresses to which alerts will be sent.

There are many other optional configuration options, see Common configuration options.

All documents must have a timestamp field. ElastAlert 2 will try to use @timestamp by default, but this can be changed with the timestamp_field option. By default, ElastAlert 2 uses ISO8601 timestamps, though unix timestamps are supported by setting timestamp_type.

As is, this rule means “Send an email to elastalert@example.com when there are more than 50 documents with some_field == some_value within a 4 hour period.”

Testing Your Rule

Running the elastalert-test-rule tool will test that your config file successfully loads and run it in debug mode over the last 24 hours:

$ elastalert-test-rule examples/rules/example_frequency.yaml

If you want to specify a configuration file to use, you can run it with the config flag:

$ elastalert-test-rule --config <path-to-config-file> examples/rules/example_frequency.yaml
The configuration preferences will be loaded as follows:
  1. Configurations specified in the yaml file.

  2. Configurations specified in the config file, if specified.

  3. Default configurations, for the tool to run.

See the testing section for more details

Running ElastAlert 2

There are two ways of invoking ElastAlert 2. As a daemon, through Supervisor (http://supervisord.org/), or directly with Python. For easier debugging purposes in this tutorial, we will invoke it directly:

$ python -m elastalert.elastalert --verbose --rule example_frequency.yaml  # or use the entry point: elastalert --verbose --rule ...
No handlers could be found for logger "Elasticsearch"
INFO:root:Queried rule Example rule from 1-15 14:22 PST to 1-15 15:07 PST: 5 hits
INFO:Elasticsearch:POST http://elasticsearch.example.com:14900/elastalert_status/elastalert_status?op_type=create [status:201 request:0.025s]
INFO:root:Ran Example rule from 1-15 14:22 PST to 1-15 15:07 PST: 5 query hits (0 already seen), 0 matches, 0 alerts sent
INFO:root:Sleeping for 297 seconds

ElastAlert 2 uses the python logging system and --verbose sets it to display INFO level messages. --rule example_frequency.yaml specifies the rule to run, otherwise ElastAlert 2 will attempt to load the other rules in the examples/rules folder.

Let’s break down the response to see what’s happening.

Queried rule Example rule from 1-15 14:22 PST to 1-15 15:07 PST: 5 hits

ElastAlert 2 periodically queries the most recent buffer_time (default 45 minutes) for data matching the filters. Here we see that it matched 5 hits:

POST http://elasticsearch.example.com:14900/elastalert_status/elastalert_status?op_type=create [status:201 request:0.025s]

This line showing that ElastAlert 2 uploaded a document to the elastalert_status index with information about the query it just made:

Ran Example rule from 1-15 14:22 PST to 1-15 15:07 PST: 5 query hits (0 already seen), 0 matches, 0 alerts sent

The line means ElastAlert 2 has finished processing the rule. For large time periods, sometimes multiple queries may be run, but their data will be processed together. query hits is the number of documents that are downloaded from Elasticsearch, already seen refers to documents that were already counted in a previous overlapping query and will be ignored, matches is the number of matches the rule type outputted, and alerts sent is the number of alerts actually sent. This may differ from matches because of options like realert and aggregation or because of an error.

Sleeping for 297 seconds

The default run_every is 5 minutes, meaning ElastAlert 2 will sleep until 5 minutes have elapsed from the last cycle before running queries for each rule again with time ranges shifted forward 5 minutes.

Say, over the next 297 seconds, 46 more matching documents were added to Elasticsearch:

INFO:root:Queried rule Example rule from 1-15 14:27 PST to 1-15 15:12 PST: 51 hits
...
INFO:root:Sent email to ['elastalert@example.com']
...
INFO:root:Ran Example rule from 1-15 14:27 PST to 1-15 15:12 PST: 51 query hits, 1 matches, 1 alerts sent

The body of the email will contain something like:

Example rule

At least 50 events occurred between 1-15 11:12 PST and 1-15 15:12 PST

@timestamp: 2015-01-15T15:12:00-08:00

If an error occurred, such as an unreachable SMTP server, you may see:

ERROR:root:Error while running alert email: Error connecting to SMTP host: [Errno 61] Connection refused

Note that if you stop ElastAlert 2 and then run it again later, it will look up elastalert_status and begin querying at the end time of the last query. This is to prevent duplication or skipping of alerts if ElastAlert 2 is restarted.

By using the --debug flag instead of --verbose, the body of email will instead be logged and the email will not be sent. In addition, the queries will not be saved to elastalert_status.

Disabling a Rule

To stop a rule from executing, add or adjust the is_enabled option inside the rule’s YAML file to false. When ElastAlert 2 reloads the rules it will detect that the rule has been disabled and prevent it from executing. The rule reload interval defaults to 5 minutes but can be adjusted via the run_every configuration option.

Optionally, once a rule has been disabled it is safe to remove the rule file, if there is no intention of re-activating the rule. However, be aware that removing a rule file without first disabling it will _not_ disable the rule!