Recording Rules in Prometheus
What are Recording Rules?
Recording rules are a powerful feature in Prometheus that allow you to precompute frequently used or computationally expensive queries and save their results as new time series. This can help reduce the load on your Prometheus server and improve performance, especially when dealing with large datasets or complex queries.
Why Use Recording Rules?
The main benefits of using recording rules include:
- Improved query performance: Precomputed results allow for faster access.
- Simplified queries: You can use the recorded metrics directly, reducing the complexity of your queries.
- Reduced load on Prometheus: By calculating results in advance, you decrease the computational burden during query time.
How to Define Recording Rules
Recording rules are defined in the Prometheus configuration file, typically in the prometheus.yml file. They can be specified under the rule_files section. Each recording rule consists of a name, a query, and an optional set of labels.
Example of a Recording Rule
Here’s a simple example:
record: job:http_inprogress_requests:sum
expr: sum(http_inprogress_requests) by (job)
This rule records the sum of all in-progress HTTP requests per job and saves it as a new time series called job:http_inprogress_requests:sum.
Using Recording Rules in Queries
Once you have defined your recording rules and Prometheus has evaluated them, you can use the resulting metrics in your queries just like any other metric. For example, to retrieve the value of the recorded metric, you can use:
Querying Recorded Metrics
job:http_inprogress_requests:sum
This query will return the sum of HTTP in-progress requests, as calculated by the recording rule.
Best Practices for Recording Rules
Here are some best practices to consider when using recording rules:
- Keep it simple: Only record metrics that are frequently used or expensive to compute.
- Use meaningful names: Choose names for your recorded metrics that clearly describe what they represent.
- Test and validate: Make sure to test your recording rules to ensure they produce the expected results.
Conclusion
Recording rules are an essential feature in Prometheus that can greatly enhance performance and simplify your monitoring setup. By precomputing and storing the results of complex queries, you can reduce load and improve responsiveness in your monitoring dashboards.