Aodh-evaluator is a component of the OpenStack Telemetry service (Aodh) that is responsible for evaluating complex alarm expressions and determining whether an alarm should be triggered or not. Aodh is an OpenStack project that provides alarming as a service for monitoring resources and generating notifications based on defined rules.
Here are some key details about Aodh-evaluator:
- Purpose: Aodh-evaluator evaluates alarm expressions defined by users and determines the current state of alarms. It takes into account the current values of the metrics being monitored and compares them with the alarm criteria to determine whether the alarm should be triggered or not.
- Alarm Expressions: Aodh allows users to define alarm expressions using the Ceilometer alarm syntax. These expressions consist of one or more rules that define the conditions under which an alarm should be triggered. Each rule consists of a metric, comparison operator, and a threshold value.
- Evaluation Engine: Aodh-evaluator utilizes a powerful evaluation engine to process the alarm expressions and calculate the current state of alarms. It fetches the latest metric data from the underlying telemetry service (Ceilometer or Gnocchi) and evaluates the expressions using the fetched data.
- Data Retrieval: Aodh-evaluator retrieves the necessary metric data from the telemetry service. It can query data from various sources, including different meters, resources, or projects, depending on the requirements specified in the alarm expressions.
- Operator Support: Aodh-evaluator supports a wide range of operators for comparing metric values in alarm expressions. These operators include greater than (gt), less than (lt), equal to (eq), not equal to (neq), greater than or equal to (ge), less than or equal to (le), etc. These operators allow users to define complex conditions based on their monitoring needs.
- State Calculation: Once the evaluation engine processes the alarm expressions and retrieves the metric data, Aodh-evaluator calculates the current state of each alarm. It determines whether the alarm is in an OK state (not triggered), ALARM state (triggered), or INSUFFICIENT DATA state (not enough data to determine the alarm state).
- Notification Generation: If an alarm is triggered, Aodh-evaluator generates notifications based on the configured notification method(s). These notifications can be sent to various endpoints, such as email, webhooks, or message queues, to inform users or external systems about the alarm condition.
- Scalability: Aodh-evaluator is designed to handle a large number of alarms and perform evaluations efficiently. It can scale horizontally by deploying multiple instances of Aodh-evaluator to distribute the evaluation workload and handle a high volume of alarms in a distributed manner.
Aodh-evaluator plays a critical role in the OpenStack Telemetry service by evaluating alarm expressions and determining the state of alarms based on the current metric data. It enables users to define complex monitoring rules and receive notifications when specific conditions are met, helping them to proactively respond to and resolve issues in their OpenStack deployments.