Exporting custom metrics and logs is available in the Shuttle Pro Tier and above.
This guide will show you how to add custom metrics and tracing events to your Shuttle application using the tracing crate.

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Getting Started

First, add the tracing dependency to your project: 
cargo add tracing

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Basic Usage

Add tracing events with fields to your functions to create custom metrics. Here’s a simple example: 
async fn hello_world() -> &'static str {
    tracing::info!(counter.hello = 1, "Hello world from OTel!");
    "Hello, world!"
}
This will:
  1. Send an info level log to stdout
  2. Export the metric to your configured telemetry provider
  3. Include the custom attribute counter.hello with value 1

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Metric Types

The runtime’s OTel exporter uses tracing-opentelemetry under the hood, which automatically handles three metric types:
  1. Monotonic Counters: Values that only increase (e.g., total requests) 
    tracing::info!(monotonic_counter.requests = 1, "New request received");
  2. Counters: Values that can increase or decrease 
    tracing::info!(counter.active_users = 1, "User logged in");
tracing::info!(counter.active_users = -1, "User logged out");
  3. Histograms: For measuring distributions of values 
    tracing::info!(histogram.request_duration_ms = 150.0, "Request completed");

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Example Trace Output

Here’s what a tracing event looks like when exported: 
{
    "attributes": {
        "code.filepath": "src/main.rs",
        "code.lineno": 4,
        "code.module_path": "my_project",
        "counter.hello": 1
    },
    "dropped_attributes_count": 0,
    "dt": "2025-02-04T15:56:27.068644985Z",
    "message": "Hello world from OTel!",
    "observed_timestamp": "2025-02-04T15:56:27.068649239Z",
    "resources": {
        "service.name": "my-project",
        "service.version": "0.1.0",
        "shuttle.deployment.env": "production",
        "shuttle.project.crate.name": "my_project",
        "shuttle.project.id": "proj_01JK8SHBZQ0XF0TKW0EDWBJ8NH",
        "shuttle.project.name": "my-project",
        "telemetry.sdk.language": "rust",
        "telemetry.sdk.name": "opentelemetry",
        "telemetry.sdk.version": "0.27.1"
    },
    "severity_number": 9,
    "severity_text": "INFO",
    "source_type": "opentelemetry"
}

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Best Practices

  1. Use Meaningful Names: Choose clear, descriptive names for your metrics 
    // Good
tracing::info!(counter.user_sessions = 1, "User session started");

// Bad
tracing::info!(counter.us = 1, "Session");
  2. Include Context: Add relevant context to your metrics 
    tracing::info!(
    counter.api_calls = 1,
    api.endpoint = "/users",
    api.method = "GET",
    "API call completed"
);
  3. Use Appropriate Metric Types:
    • Use monotonic_counter for values that only increase
    • Use counter for values that can go up and down
    • Use histogram for measuring distributions

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