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Adding a New Scraper

This guide walks you through the process of adding a new scraper type.

You can use our code tour by using the CodeTour extension for VS Code and/or use it in GitHub Codespaces.

📢 Before implementing a new scraping type, please open an issue to discuss your scenario

Implementing a Scaler

Configuration

  1. Add your new scraping type to the ResourceType enum in Promitor.Core.Contracts.
  2. Describe the resource for which you're scraping metrics by creating <New-Type>ResourceDefinition and inherit from Promitor.Core.Scraping.Configuration.Model.Metrics.AzureResourceDefinition - this class should go in .\src\Promitor.Core.Contracts\ResourceTypes.
  3. Describe the resource configuration for which you're scraping metrics by creating <New-Type>ResourceV1 and inherit from Promitor.Core.Scraping.Configuration.Serialization.v1.Model.AzureResourceDefinitionV1 - this class should go in .\src\Promitor.Core.Scraping\Configuration\Serialization\v1\Model\ResourceTypes.
  4. Create a new Deserializer in .\src\Promitor.Core.Scraping\Configuration\Serialization\v1\Providers. This must inherit from ResourceDeserializer.
  5. Update Promitor.Core.Scraping.Configuration.v1.Core.AzureResourceDeserializerFactory to handle your new resource type by returning a new instance of the Deserializer you created in the previous step.
  6. Update the Promitor.Core.Scraping.Configuration.Serialization.v1.Mapping.V1MappingProfile so that it:
  • Is able to map your new resource type by mapping the <New-Type>ResourceV1 to <New-Type>ResourceDefinition
  • Annotate how to map it with IAzureResourceDefinition (include).
  1. Provide a unit test in .\src\Promitor.Tests.Unit\Serialization\v1\Providers that tests the deserialization based on our sample. Your test class must inherit from ResourceDeserializerTest to ensure the inherited functionality is tested.

Going forward in this guide, TResourceDefinition will refer to your newly created configuration type.

Validation

For every scraper type we provide validation for the configuration so that Promitor fails to start up.

This requires the following steps:

  1. Create a new validator that implements IMetricValidator. This validator should reside in .\src\Promitor.Agents.Scraper\Validation\MetricDefinitions\ResourceTypes. You can look at the contents of ServiceBusQueueMetricValidator for an idea of the validation inputs, steps, and outputs typical of validator implementation.
  2. Add construction and usage of this validator to .\src\Promitor.Agents.Scraper\Validation\Factories\MetricValidatorFactory.cs for the ResourceType you created in step #1 above.
  3. Provide a unit test for every validation rule that was added in .\src\Promitor.Tests.Unit\Validation\Scraper\Metrics\ResourceTypes

Scraping

We'll add a new scraper that pulls the metrics from Azure Monitor:

  1. Implement a scraper, that inherits from AzureMonitorScraper<TResourceDefinition>, which will specify what resource to scrape with Azure Monitor.
    • You can find it in .\src\Promitor.Core.Scraping\ResourceTypes.
  2. Hook your new scraper in our MetricScraperFactory which determines what scraper to use for the passed configuration.
    • You can find it in .\src\Promitor.Core.Scraping\Factories.

Resource Discovery

We'll add dynamic resource discovery support by using Azure Resource Graph:

  1. Implement a new discovery query that create an Azure Resource Graph query.It should inherits from ResourceDiscoveryQuery and be located in .\src\Promitor.Agents.ResourceDiscovery\Graph\ResourceTypes
  2. Support the new resource type in ResourceDiscoveryFactory

📝 Currently we don't have integration tests

Writing Integration Tests

Every new scraper, should be automatically tested to ensure that it can be scraped.

To achieve this, the steps are fairly simple:

  1. Provision a new test resource in our testing infrastructure (GitHub)
  2. Define a new resource discovery group
    • You can find it on config\promitor\resource-discovery\resource-discovery-declaration.yaml
  3. Define a new metric in the scraper configuration with a valid Azure Monitor metric for the service (overview]
    • You can find it on config\promitor\scraper\metrics.yaml

Our testing infrastructure will pick up the new metric automatically and ensure that it is being reported!

Documentation

Features are great to have but without clear & well-written documentation they are somewhat useless.

The documentation for Promitor is hosted on docs.promitor.io and is maintained in promitor/docs.

Please follow the instructions in the docs contribution guide for documenting a new scraper.

Changelog

New scalers are a great additions and we should make sure that they are listed in our changelog.

Learn about our changelog in our contribution guide.

See It In Action

Now that you are done, make sure you run Promitor locally so verify that it generates the correct metrics!

When opening the pull request (PR), feel free to copy the generated Prometheus metrics for review.

Learn how to run it in our development guide.