rust-logging

name	rust-logging
description	Use when setting up tracing, configuring log levels, writing structured logs, using spans and instrument, or handling sensitive data in Rust logs.

Rust Logging Standards

Core Rules

• Framework: tracing + tracing-subscriber
• Format: pretty print in dev, JSON in production
• Output: stdout
• Language: all log messages in English

Log Levels

Level	Purpose	Example
ERROR	Requires alerting and human intervention	Database connection failed
WARN	Needs attention but system can self-heal	Retry succeeded after transient failure
INFO	Business events, visible in production	Order created/completed
DEBUG	Development debugging, disabled in prod	SQL queries, intermediate values
TRACE	Extreme detail, only for hard-to-diagnose issues	Function entry/exit

# Production
RUST_LOG=info,my_app=debug

# Development
RUST_LOG=debug,my_app=trace,sqlx=warn

Structured Logging

Use snake_case field names:

tracing::info!(
    request_id = %request_id,
    user_id = %user_id,
    order_id = %order.id,
    duration_ms = elapsed.as_millis() as u64,
    "order completed"
);

Common fields: request_id, user_id, order_id, duration_ms, error, path, method, status

Span Usage

#[tracing::instrument(
    name = "create_order",
    skip(self, cmd),
    fields(user_id = %cmd.user_id, product_id = %cmd.product_id)
)]
pub async fn create_order(&self, cmd: CreateOrderCommand) -> Result<Order, AppError> {
    // ...
}

• Always skip large or non-Display arguments (self, request bodies, DB pools).
• Use fields(...) to attach key context to the span.

Sensitive Data

Never log: passwords, API keys, tokens, credit card numbers, personal IDs.

// Use the secrecy crate
use secrecy::Secret;

pub struct Config {
    pub api_key: Secret<String>,  // Displays as [REDACTED] in logs
}

Error Logging

// ERROR: requires alerting
tracing::error!(error = ?err, "database connection failed");

// WARN: needs attention
tracing::warn!(error = ?err, attempt = attempt, "retry after failure");

// INFO: expected business error
tracing::info!(error = %err, "validation failed");

• ?err — preserves the full error chain (Debug format)
• %err — logs only the Display message

Checklist

• Use tracing macros, never println! or log
• All log messages in English
• Key business operations logged at INFO level
• Errors use the correct severity level
• Include request_id for distributed tracing
• Sensitive data is redacted
• Use structured fields instead of string concatenation