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Custom Metrics Autoscaling

Porter supports autoscaling based on custom Prometheus metrics, allowing you to scale your services based on application-specific signals like queue length, request latency, or business metrics. For other autoscaling options, see the Autoscaling overview.

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Configuring Metrics Scraping

Note: Metrics scraping is only available for web services. You can configure Porter to scrape metrics from your application’s /metrics endpoint. This is useful for:
  • Collecting application-specific metrics
  • Setting up custom autoscaling based on your metrics
  • Monitoring application performance

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How to Enable Metrics Scraping

  1. Navigate to your application dashboard
  2. Select your web service
  3. Go to the Advanced tab under service settings
  4. Find the Metrics scraping section
  5. Enable Enable metrics scraping
  6. Configure the following options:
    • Port: The port where your metrics endpoint is exposed (defaults to your web service’s default port)
    • Path: The path where metrics are exposed (defaults to /metrics)
Important: Our telemetry collector will automatically send requests to the specified port and path to collect metrics from your service. Metrics Scraping Configuration Metrics scraping configuration in the Advanced tab of a web service

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Prometheus Metrics Format

Your application must expose metrics in Prometheus format:
  • Metrics are exposed as HTTP endpoints (typically /metrics)
  • Each metric follows the format: metric_name{label1="value1",label2="value2"} value
  • Common metric types:
    • Counter: Values that only increase (e.g., http_requests_total)
    • Gauge: Values that can go up and down (e.g., queue_length)
    • Histogram: Observations distributed into buckets (e.g., request_duration_seconds)
Example metrics output: 
# HELP http_requests_total Total number of HTTP requests
# TYPE http_requests_total counter
http_requests_total{method="post",code="200"} 1027
http_requests_total{method="get",code="200"} 2048
For detailed information about implementing Prometheus metrics in your application, refer to:

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Configuring Custom Autoscaling

With metrics scraping enabled, you can set up autoscaling based on your custom metrics.

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How to Configure

  1. Navigate to your application dashboard
  2. Select your service
  3. Go to the Resources tab
  4. Configure basic autoscaling:
    • Enable Autoscaling
    • Set Min instances (e.g., 1)
    • Set Max instances (e.g., 10)
  5. Switch to custom metrics mode by clicking the customize icon
  6. Configure custom metrics:
    • Metric Name: Select a metric from your exposed Prometheus metrics
    • Query: Write or modify the PromQL query (defaults to avg(<metric_name>))
    • Threshold: Set the threshold value that triggers scaling
When your selected metric exceeds the threshold, Porter will automatically scale your service between the min and max instances you’ve specified. Custom Autoscaling Configuration Custom autoscaling configuration in the Resources tab of a service

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Query Requirements

Your PromQL query must return a single numeric value (scalar). Valid query examples:
  • avg(metric_name) → Returns a single average value
  • sum(rate(http_requests_total[5m])) → Returns a single sum value
  • max(queue_length) → Returns a single maximum value
Invalid queries:
  • Vector results (multiple time series)
  • String results
  • No data/empty results
If your query returns multiple values, use aggregation operators like avg(), sum(), or max() to reduce it to a single value.

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Switching Between Autoscaling Modes

You can switch between:
  • Default Mode: Autoscale based on CPU/Memory usage
  • Custom Mode: Autoscale based on your application metrics
Click the customize/restore icons to switch between modes.

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Example: Message Queue Consumer

Consider a data processing pipeline with a web API and worker service:

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Analytics Ingestion API

A web service that ingests events and publishes them to RabbitMQ for processing. 
from prometheus_client import generate_latest, Gauge

# Track messages in RabbitMQ queues
queue_metrics = Gauge('rabbitmq_queue_messages',
                     'Number of messages in queue',
                     ['queue_name'])

@app.route('/metrics')
def metrics():
    queue_metrics.labels(queue_name='user_events').set(
        rabbit_connection.get_queue_length('user_events'))
    queue_metrics.labels(queue_name='system_events').set(
        rabbit_connection.get_queue_length('system_events'))
    return generate_latest()

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Event Processing Worker

A worker service that processes events from RabbitMQ. Custom Autoscaling Configuration:
  • Metric Name: rabbitmq_queue_messages{queue_name="user_events"}
  • Query: sum(rabbitmq_queue_messages{queue_name="user_events"})
  • Threshold: 1000 (scale up when more than 1000 events are waiting)
With this setup, Porter will add more workers when the queue backs up and scale down when the queue is processed.