Reduce alert fatigue with event filters
Sensu event filters allow you to filter events destined for one or more event handlers. Sensu event filters evaluate their expressions against the observation data in events to determine whether the event should be passed to an event handler.
Use event filters to customize alert policies, improve contact routing, eliminate notification noise from recurring events, and filter events from systems in pre-production environments.
In this guide, you learn how to reduce alert fatigue by configuring an event filter named
hourly for a handler named
slack to prevent alerts from being sent to Slack every minute.
If you don’t already have a handler in place, follow Send Slack alerts with handlers before continuing with this guide.
You can use either of two approaches to create the event filter to handle occurrences:
Approach 1: Use sensuctl to create an event filter
First, create an event filter called
hourly that matches new events (where the event’s
occurrences is equal to
1) or hourly events (every hour after the first occurrence, calculated with the check’s
interval and the event’s
Events in Sensu Go are handled regardless of check execution status. Even successful check events are passed through the pipeline, so you’ll need to add a clause for non-zero status.
sensuctl filter create hourly \ --action allow \ --expressions "event.check.occurrences == 1 || event.check.occurrences % (3600 / event.check.interval) == 0"
Assign the event filter to a handler
Now that you’ve created the
hourly event filter, you can assign it to a handler.
Because you want to reduce the number of Slack messages Sensu sends, you’ll apply the event filter to an existing handler named
slack, in addition to the built-in
is_incident filter, so only failing events are handled.
sensuctl handler update slack
Follow the prompts to add the
is_incident event filters to the Slack handler.
Create a fatigue check event filter
Although you can use
sensuctl to interactively create a filter, you can create more reusable filters with dynamic runtime assets.
Read on to see how to implement a filter using this approach.
Approach 2: Use an event filter dynamic runtime asset
If you’re not already familiar with dynamic runtime assets, please take a moment to read Use assets to install plugins. This will help you understand what dynamic runtime assets are and how they are used in Sensu.
In this approach, the first step is to obtain an event filter dynamic runtime asset that will allow you to replicate the behavior of the
hourly event filter created in Approach 1 via
sensuctl asset add nixwiz/sensu-go-fatigue-check-filter:0.3.2 -r fatigue-filter fetching bonsai asset: nixwiz/sensu-go-fatigue-check-filter:0.3.2 added asset: nixwiz/sensu-go-fatigue-check-filter:0.3.2 You have successfully added the Sensu asset resource, but the asset will not get downloaded until it's invoked by another Sensu resource (ex. check). To add this runtime asset to the appropriate resource, populate the "runtime_assets" field with ["fatigue-filter"].
This example uses the
-r (rename) flag to specify a shorter name for the asset:
You can also download the asset directly from Bonsai, the Sensu asset index.
NOTE: Sensu does not download and install dynamic runtime asset builds onto the system until they are needed for command execution. Read the asset reference for more information about dynamic runtime asset builds.
You’ve registered the dynamic runtime asset, but you still need to create the filter. To do this, use the following configuration:
--- type: EventFilter api_version: core/v2 metadata: name: fatigue_check namespace: default spec: action: allow expressions: - fatigue_check(event) runtime_assets: - fatigue-filter
Then, create the filter, naming it
sensuctl create -f sensu-fatigue-check-filter.yml
Now that you’ve created the filter dynamic runtime asset and the event filter, you can create the check annotations you need for the dynamic runtime asset to work properly.
Annotate a check for filter dynamic runtime asset use
Next, you need to make some additions to any checks you want to use the filter with. Here’s an example CPU check:
--- type: CheckConfig api_version: core/v2 metadata: name: linux-cpu-check namespace: default annotations: fatigue_check/occurrences: '1' fatigue_check/interval: '3600' fatigue_check/allow_resolution: 'false' spec: command: check-cpu -w 90 c 95 env_vars: handlers: - email high_flap_threshold: 0 interval: 60 low_flap_threshold: 0 output_metric_format: '' output_metric_handlers: proxy_entity_name: '' publish: true round_robin: false runtime_assets: stdin: false subdue: subscriptions: - linux timeout: 0 ttl: 0
Notice the annotations under the
The annotations are required for the filter dynamic runtime asset to work the same way as the interactively created event filter.
Specifically, the annotations in this check definition are doing several things:
fatigue_check/occurrences: Tells the event filter on which occurrence to send the event for further processing
fatigue_check/interval: Tells the event filter the interval at which to allow additional events to be processed (in seconds)
fatigue_check/allow_resolution: Determines whether to pass a
resolveevent through to the filter
For more information about configuring these values, see the filter dynamic runtime asset’s README. Next, you’ll assign the newly minted event filter to a handler.
Assign the event filter to a handler
Just like with the interactively created event filter, you’ll introduce the filter into your Sensu workflow by configuring a handler to use it. Here’s an example:
--- api_version: core/v2 type: Handler metadata: namespace: default name: slack spec: type: pipe command: 'sensu-slack-handler --channel ''#general'' --timeout 20 --username ''sensu'' ' env_vars: - SLACK_WEBHOOK_URL=https://www.webhook-url-for-slack.com timeout: 30 filters: - is_incident - fatigue_check
Validate the event filter
Verify the proper behavior of these event filters with
The default location of these logs varies based on the platform used (see Troubleshoot Sensu for details).
Whenever an event is being handled, a log entry is added with the message
"handler":"slack","level":"debug","msg":"sending event to handler", followed by
a second log entry with the message
"msg":"pipelined executed event pipe handler","output":"","status":0.
However, if the event is being discarded by the event filter, a log entry with the message
event filtered will appear instead.
Now that you know how to apply an event filter to a handler and use a filter dynamic runtime asset to help reduce alert fatigue, read the filters reference for in-depth information about event filters.