A Percentage Match alert matches when the percentage of documents within a match_bucket_filter within a calculation window (by default buffer_time) is higher or lower than a relative percentage value max_percentage.
This would allow you to receive alerts in scenarios such as If there is a 20% increase max_percentage in the number of 500 errors match_bucket_filter within a 15 minutes timeframe buffer_time you would receive an alert to your configured channel. Here is an example below:
name: "Percentage match example"
type: percentage_match
index: "*-*"
filter:
- query:
query_string:
query: "agent.hostname:azure"
match_bucket_filter:
- query_string:
query: "router.status: [500 TO 599]"
doc_type: _doc
max_percentage: 20
buffer_time:
minutes: 3
alert:
- "email"
email:
- "example@logit.io"
Additional Options
In addition, you can also provide a filter query to limit the initial results that the match_bucket_filter will be applied to.
What's next?
Read Logit.io's introduction to alerting
Learn more about ElastAlert rules: if you'd like to learn more about ElastAlert rules from the people that built it, check out their cheat sheet.