Prometheus Chart a Range Query and Pull Its Exemplars

arazzo: 1.0.1
info:
  title: Prometheus Chart a Range Query and Pull Its Exemplars
  summary: Validate an expression, graph it over a time range, then link the spikes to traces.
  description: >-
    The flow behind every Prometheus-backed dashboard panel that supports
    click-through to tracing. The workflow validates the PromQL expression with a
    cheap instant query, evaluates it across the full time range at a step
    interval to produce the matrix a chart needs, and then retrieves the
    exemplars over the same window so high-value samples can be linked to their
    trace IDs. Every step spells out its request inline so the flow can be read
    and executed without opening the underlying OpenAPI description.
  version: 1.0.0
sourceDescriptions:
- name: httpApi
  url: ../openapi/prometheus-http-api-openapi.yml
  type: openapi
workflows:
- workflowId: range-query-with-exemplars
  summary: Evaluate a PromQL expression over a time range and fetch its exemplars.
  description: >-
    Validating the expression with an instant query before issuing the range
    query keeps a malformed or overly expensive expression from being evaluated
    at every step across the whole window.
  inputs:
    type: object
    required:
    - query
    - start
    - end
    - step
    properties:
      query:
        type: string
        description: >-
          The PromQL expression to chart (e.g.
          histogram_quantile(0.99, rate(http_request_duration_seconds_bucket[5m]))).
      start:
        type: string
        description: Start of the range as a Unix timestamp or RFC3339 string.
      end:
        type: string
        description: End of the range as a Unix timestamp or RFC3339 string.
      step:
        type: string
        description: Resolution step width as a duration string (e.g. 15s, 1m, 1h).
  steps:
  - stepId: validateExpression
    description: >-
      Evaluate the expression once at the end of the window. A 400 or 422 here
      means the expression is malformed and the range query would fail the same
      way, only after far more work on the server.
    operationId: queryInstant
    parameters:
    - name: query
      in: query
      value: $inputs.query
    - name: time
      in: query
      value: $inputs.end
    - name: timeout
      in: query
      value: 30s
    successCriteria:
    - condition: $statusCode == 200
    - condition: $response.body#/status == "success"
    outputs:
      resultType: $response.body#/data/resultType
      sampleCount: $response.body#/data/result
  - stepId: evaluateRange
    description: >-
      Evaluate the expression at every step across the range, producing the
      matrix of time series a chart renders.
    operationId: queryRange
    parameters:
    - name: query
      in: query
      value: $inputs.query
    - name: start
      in: query
      value: $inputs.start
    - name: end
      in: query
      value: $inputs.end
    - name: step
      in: query
      value: $inputs.step
    - name: timeout
      in: query
      value: 60s
    successCriteria:
    - condition: $statusCode == 200
    - condition: $response.body#/status == "success"
    - condition: $response.body#/data/resultType == "matrix"
    outputs:
      resultType: $response.body#/data/resultType
      series: $response.body#/data/result
      firstSeriesMetric: $response.body#/data/result/0/metric
      firstSeriesValues: $response.body#/data/result/0/values
  - stepId: fetchExemplars
    description: >-
      Retrieve exemplars over the same window. Exemplars carry the trace or log
      IDs attached to individual observations, which is what turns a latency
      spike on the chart into a specific trace to open.
    operationId: queryExemplars
    parameters:
    - name: query
      in: query
      value: $inputs.query
    - name: start
      in: query
      value: $inputs.start
    - name: end
      in: query
      value: $inputs.end
    successCriteria:
    - condition: $statusCode == 200
    - condition: $response.body#/status == "success"
    outputs:
      exemplarData: $response.body#/data
      firstSeriesLabels: $response.body#/data/0/seriesLabels
      firstExemplars: $response.body#/data/0/exemplars
  outputs:
    series: $steps.evaluateRange.outputs.series
    resultType: $steps.evaluateRange.outputs.resultType
    exemplarData: $steps.fetchExemplars.outputs.exemplarData