Sensu Go Fatigue Check Filter

• Overview
• Usage examples
• Configuration
  • Sensu Go
    • Asset registration
    • Asset definition
    • Filter definition
    • Handler definition
    • Check definition
    • Entity definition
    • Keepalives
    • Cron scheduled checks
    • Annotations
    • Arguments
    • Non-repeating alerts
• Installation from source
• Additional notes
• Contributing

Overview

The Sensu Go Fatigue Check Filter is a Sensu Event Filter for managing alert fatigue.

A typical use of filters is to reduce alert fatigue. One of the most typical examples of this is create the following filter that only passes through events on their first occurrence and every hour after that.

---
type: EventFilter
api_version: core/v2
metadata:
  name: hourly
  namespace: default
spec:
  action: allow
  expressions:
  - event.check.occurrences == 1 || event.check.occurrences % (3600 / event.check.interval)
    == 0
  runtime_assets: []

However, the use of the filter above creates some limitations. Suppose you have one check in particular that you want to change to only alert after three (3) occurrences. Typically that might mean creating another handler and filter pair to assign to that check. If you have to do this often enough and you start to have an unwieldy mass of handlers and filters.

That's where this Fatigue Check Filter comes in. Using annotations, it makes the number of occurrences and the interval tunable on a per-check or per-entity basis. It also allows you to control whether or not resolution events are passed through.

Usage examples

N/A

Configuration

Sensu Go

Asset registration

Assets are the best way to make use of this plugin. If you're not using an asset, please consider doing so! If you're using sensuctl 5.13 or later, you can use the following command to add the asset:

sensuctl asset add sensu/sensu-go-fatigue-check-filter --rename fatigue-check-filter

Note that the --rename is not necessary, but references to the runtime asset in the filter definition as in the example below would need to be updated to match.

If you're using an earlier version of sensuctl, you can download the asset definition from this project's Bonsai asset index page.

You can create your own asset by creating a tar file containing lib/fatigue_check.js and creating your asset definition accordingly.

Asset definition

If not using sensuctl asset add:

---
type: Asset
api_version: core/v2
metadata:
  name: fatigue-check-filter
  namespace: default
spec:
  sha512: 2e67975df7d993492cd5344edcb9eaa23b38c1eef7000576b396804fc2b33362b02a1ca2f7311651c175c257b37d8bcbbce1e18f6dca3ca04520e27fda552856
  url: http://example.com/sensu/assets/fatigue-check.tar.gz

Filter definition

---
type: EventFilter
api_version: core/v2
metadata:
  name: fatigue_check
  namespace: default
spec:
  action: allow
  expressions:
  - fatigue_check(event)
  runtime_assets:
  - fatigue-check-filter

Handler definition

---
type: Handler
api_version: core/v2
metadata:
  namespace: default
  name: email
spec:
  type: pipe
  command: sensu-email-handler -f [email protected] -t [email protected] -s smtp.example.com
    -u emailuser -p sup3rs3cr3t
  timeout: 10
  filters:
  - is_incident
  - not_silenced
  - fatigue_check

Check definition

---
type: CheckConfig
api_version: core/v2
metadata:
  name: linux-cpu-check
  namespace: default
  annotations:
    fatigue_check/occurrences: '3'
    fatigue_check/interval: '900'
    fatigue_check/allow_resolution: 'false'
spec:
  command: check-cpu -w 90 c 95
  handlers:
  - email
  interval: 60
  publish: true
  runtime_assets: 
  subscriptions:
  - linux

Entity definition

Via the agent.yml:

---
##
# agent configuration
##

#name: ""

#namespace: "default"

#subscriptions: 
#  - "localhost"

annotations:
  fatigue_check/occurrences: "3"
  fatigue_check/interval: "900"
  fatigue_check/keepalive_occurrences: "1"
  fatigue_check/keepalive_interval: "300"
  fatigue_check/allow_resolution: "false"

[...]

Keepalives

Keepalives do not have check resources with annotations that can be used to tune this filter. Using standard entity annotations would override the settings for all other checks. To address this specific case, two additional tunables exist for customizing this filter for keepalive events. These can be set as arguments to the fatigue_check() function in the filter definition or as entity annotations to override the defaults on a per entity basis.

Cron scheduled checks

Since cron scheduled checks do not provide an explicit interval, this filter has to compute the apparent interval using the history available in the event. In order for this to work, there has to be at least two entries in the event's check history. The only time there would be less than two history entries is during the first two check executions. By default this should not be an issue, but in the unlikely case the interval is set this low, a default interval of 60 seconds is used.

Annotations

The Fatigue Check Filter makes use of four annotations within the check and/or entity metadata for normal checks with an additional two keepalive annotations availalbe in the entity metadata. The entity annotations taking precedence over check annotations. All annotations take precedence of the fatigue_check() function arguments and defaults.

Annotation	Default	Usage
fatigue_check/occurrences	1	On which occurrence to allow the initial event to pass through for normal checks
fatigue_check/interval	1800	In seconds, at what interval to allow subsequent events to pass through, ideally a multiple of the check interval for normal checks
fatigue_check/allow_resolution	true	Determines whether or not a resolution event is passed through
fatigue_check/suppress_flapping	true	Determines whether or not to suppress events for checks that are marked as flapping
fatigue_check/keepalive_occurrences	1	On which occurrence to allow the initial event to pass through for keepalives (entity only)
fatigue_check/keepalive_interval	1800	In seconds, at what interval to allow subsequent events to pass through, ideally a multiple of the check interval for keepalives (entity only)

Arguments

The fatigue_check() function can take up to five arguments.

fatigue_check(event, occurrences, interval, keepalive_occurrences, keepalive_interval)

The first one is the event and is required. The remaining four are optional and allow you to override the built-in defaults for occurrences, interval, keepalive_occurrences, and keepalive_interval, respectively. For example, if you'd like a version of the filter that, by default on non-keepalive checks, matches on the second occurrence instead of the first you could create a filter similar to below:

---
type: EventFilter
api_version: core/v2
metadata:
  name: fatigue_check_two_occurrences
  namespace: default
spec:
  action: allow
  expressions:
  - fatigue_check(event, 2)
  runtime_assets:
  - fatigue-check-filter

If you'd like one that overrides the default 30 minute interval for non-keepalive checks with a 10 minute one you could create one similar to below (note that in order to specify the third argument, you have to provide the second):

---
type: EventFilter
api_version: core/v2
metadata:
  name: fatigue_check_10m_interval
  namespace: default
spec:
  action: allow
  expressions:
  - fatigue_check(event, 1, 600)
  runtime_assets:
  - fatigue-check-filter

If you'd like one that overrides the default occurrences for keeaplives and alerts on the second occurrence rather than the first you could create one similar to below (note that in order to specify the fourth argument, you have to provide the second and third):

---
type: EventFilter
api_version: core/v2
metadata:
  name: fatigue_check_two_occurrences
  namespace: default
spec:
  action: allow
  expressions:
  - fatigue_check(event, 1, 1800, 2)
  runtime_assets:
  - fatigue-check-filter

If you'd like one that overrides the default 30 minute interval for keepalives with a 10 minute one you could create one similar to below (note that in order to specify the fifth argument, you have to provide the second, third, and fourth as well, even if you want the defaults):

---
type: EventFilter
api_version: core/v2
metadata:
  name: fatigue_check_10m_interval
  namespace: default
spec:
  action: allow
  expressions:
  - fatigue_check(event, 1, 1800, 1, 600)
  runtime_assets:
  - fatigue-check-filter

Non-repeating alerts

If you need to have alerts which will not repeat, meaning the alert is only ever sent on the first occurrence and none after (aside from the resolution, if allow_resolution is true, which is the default), then you will need to set the interval (or keepalive_interval) to zero (0) via an annotation.

Installation from source

Sensu Go

See the instructions above for asset registration.

Additional notes

• This filter makes use of the occurrences_watermark attribute that was buggy up until Sensu Go 5.9. Your mileage may vary on prior versions.

• If the interval is not a multiple of the check's interval, then the actual interval is computed by rounding up the result of dividing the interval by the check's interval. For example, an interval of 180s with a check interval of 25s would pass the event through on every 8 occurrences (200s).

Contributing

Please submit an issue if you have problems or suggestions.