Alerting allows you to define *rules* to detect complex conditions within different {kib} apps and trigger actions when those conditions are met. Alerting is integrated with {observability-guide}/create-alerts.html[*Observability*], {security-guide}/prebuilt-rules.html[*Security*], <<geo-alerting,*Maps*>> and {ml-docs}/ml-configuring-alerts.html[*{ml-app}*], can be centrally managed from the <<management,*Management*>> UI, and provides a set of built-in <<action-types, connectors>> and <<rule-types, rules>> (known as stack rules) for you to use.
Alerting works by running checks on a schedule to detect conditions defined by a *rule*. When a condition is met, the rule tracks it as an *alert* and responds by triggering one or more *actions*.
Actions typically involve interaction with {kib} services or third party integrations. *Connectors* allow actions to talk to these services and integrations.
For example, when monitoring a set of servers, a rule might check for average CPU usage > 0.9 on each server for the last two minutes (condition), checked every minute (schedule), sending a warning email message via SMTP with subject `CPU on {{server}} is high` (action).
Under the hood, {kib} rules detect conditions by running a javascript function on the {kib} server, which gives it the flexibility to support a wide range of conditions, anything from the results of a simple {es} query to heavy computations involving data from multiple sources or external systems.
For example, an <<rule-type-index-threshold, index threshold rule type>> lets you specify the index to query, an aggregation field, and a time window, but the details of the underlying {es} query are hidden.
The intervals of rule checks in {kib} are approximate. The timing of their execution is affected by factors such as the frequency at which tasks are claimed and the task load on the system. See <<alerting-production-considerations, Alerting production considerations>> for more information.
Actions are invocations of connectors, which allow interaction with {kib} services or integrations with third-party systems. Actions run as background tasks on the {kib} server when rule conditions are met.
The result is a template: all the parameters needed to invoke a service are supplied except for specific values that are only known at the time the rule condition is detected.
In the server monitoring example, the `email` connector type is used, and `server` is mapped to the body of the email, using the template string `CPU on {{server}} is high`.
When the rule detects the condition, it creates an <<alerting-concepts-alert-instances, alert>> containing the details of the condition, renders the template with these details such as server name, and executes the action on the {kib} server by invoking the `email` connector type.
When checking for a condition, a rule might identify multiple occurrences of the condition. {kib} tracks each of these *alerts* separately and takes an action per alert.
Using the server monitoring example, each server with average CPU > 0.9 is tracked as an alert. This means a separate email is sent for each server that exceeds the threshold.
Since actions are executed per alert, a rule can end up generating a large number of actions. Take the following example where a rule is monitoring three servers every minute for CPU usage > 0.9:
In the above example, three emails are sent for server X123 in the span of 3 minutes for the same rule. Often it's desirable to suppress frequent re-notification. Operations like muting and throttling can be applied at the alert level. If we set the rule re-notify interval to 5 minutes, we reduce noise by only getting emails for new servers that exceed the threshold:
*Connectors* provide a central place to store connection information for services and integrations. For example if four rules send email notifications via the same SMTP service, they can all reference the same SMTP connector. When the SMTP settings change, you can update them once in the connector, instead of having to update four rules.
A *rule* consists of conditions, *actions*, and a schedule. When conditions are met, *alerts* are created that render *actions* and invoke them. To make action setup and update easier, actions use *connectors* that centralize the information used to connect with {kib} services and third-party integrations. The following example ties these concepts together:
. Anytime a *rule*'s conditions are met, an *alert* is created. This example checks for servers with average CPU > 0.9. Three servers meet the condition, so three alerts are created.
. Alerts create *actions* as long as they are not muted or throttled. When actions are created, the template that was setup in the rule is filled with actual values. In this example, three actions are created, and the template string {{server}} is replaced with the server name for each alert.
. {kib} invokes the actions, sending them to a third party *integration* like an email service.
. If the third party integration has connection parameters or credentials, {kib} will fetch these from the *connector* referenced in the action.
{kib} alerting and <<watcher-ui, {es} alerting>> are both used to detect conditions and can trigger actions in response, but they are completely independent alerting systems.
* {kib} <<alerting-concepts-conditions, rules hide the details of detecting conditions>> through *rule types*, whereas watches provide low-level control over inputs, conditions, and transformations.
* {kib} rules track and persist the state of each detected condition through *alerts*. This makes it possible to mute and throttle individual alerts, and detect changes in state such as resolution.
* Actions are linked to *alerts* in {kib} alerting. Actions are fired for each occurrence of a detected condition, rather than for the entire rule.
At a higher level, {kib} alerting allows rich integrations across use cases like <<xpack-apm,*APM*>>, <<metrics-app,*Metrics*>>, <<xpack-siem,*Security*>>, and <<uptime-app,*Uptime*>>.
Pre-packaged *rule types* simplify setup and hide the details of complex, domain-specific detections, while providing a consistent interface across {kib}.
* You must enable Transport Layer Security (TLS) for communication <<configuring-tls-kib-es, between {es} and {kib}>>. {kib} alerting uses <<api-keys, API keys>> to secure background rule checks and actions, and API keys require {ref}/configuring-tls.html#tls-http[TLS on the HTTP interface]. A proxy will not suffice.
When relying on alerting and actions as mission critical services, make sure you follow the <<alerting-production-considerations,Alerting production considerations>>.
Also note that a user will need +read+ privileges for the *Actions and Connectors* feature to attach actions to a rule or to edit a rule that has an action attached to it.
Rules and connectors are isolated to the {kib} space in which they were created. A rule or connector created in one space will not be visible in another.
Rules, including all background detection and the actions they generate are authorized using an <<api-keys, API key>> associated with the last user to edit the rule. Upon creating or modifying a rule, an API key is generated for that user, capturing a snapshot of their privileges at that moment in time. The API key is then used to run all background tasks associated with the rule including detection checks and executing actions.
If a rule requires certain privileges to run, such as index privileges, keep in mind that if a user without those privileges updates the rule, the rule will no longer function.
For security reasons you may wish to limit the extent to which {kib} can connect to external services. <<action-settings>> allows you to disable certain <<action-types>> and allowlist the hostnames that {kib} can connect with.