Migrating from setup_logging() to FastAPIBuilder

This guide helps you migrate from the deprecated setup_logging() function to the new FastAPIBuilder class.

Why migrate?

FastAPIBuilder provides:

Full configuration access: All AsyncLoggerBuilder methods (backpressure, sampling, redaction, queue size, etc.)
Environment variable support: FastAPI-specific env vars with override warnings
Consistent API: Same builder pattern as regular logger configuration
Better discoverability: IDE autocompletion for all options

Quick migration

Before (deprecated)

from fapilog.fastapi import setup_logging

app = FastAPI(
    lifespan=setup_logging(
        preset="production",
        skip_paths=["/health", "/metrics"],
        sample_rate=0.1,
        include_headers=True,
        allow_headers=["content-type", "user-agent"],
        log_errors_on_skip=True,
    )
)

After (recommended)

from fapilog.fastapi import FastAPIBuilder

app = FastAPI(
    lifespan=FastAPIBuilder()
        .with_preset("production")
        .skip_paths(["/health", "/metrics"])
        .sample_rate(0.1)
        .include_headers(["content-type", "user-agent"])
        .log_errors_on_skip(True)
        .build()
)

Parameter mapping

setup_logging() parameter	FastAPIBuilder method
`preset="production"`	`.with_preset("production")`
`skip_paths=[...]`	`.skip_paths([...])`
`sample_rate=0.1`	`.sample_rate(0.1)`
`include_headers=True`	Not needed (use `.include_headers()`)
`allow_headers=[...]`	`.include_headers([...])`
`log_errors_on_skip=True`	`.log_errors_on_skip(True)`
`redact_headers=[...]`	Use middleware directly
`additional_redact_headers=[...]`	Use middleware directly

Advanced configuration

With FastAPIBuilder, you now have access to all core fapilog options:

app = FastAPI(
    lifespan=FastAPIBuilder()
        .with_preset("production")
        # FastAPI-specific
        .skip_paths(["/health"])
        .sample_rate(0.1)
        # Core options (not available with setup_logging)
        .with_backpressure(drop_on_full=False)
        .with_sampling(rate=0.1)  # Log-level sampling
        .with_redaction(preset="GDPR_PII")
        .with_queue_size(50000)
        .with_batch_size(100)
        .add_cloudwatch("/myapp/prod")
        .build()
)

Environment variables

FastAPI-specific settings can now be configured via environment variables:

# FastAPI-specific env vars
FAPILOG_FASTAPI__SKIP_PATHS=/health,/metrics,/ready
FAPILOG_FASTAPI__INCLUDE_HEADERS=content-type,user-agent
FAPILOG_FASTAPI__SAMPLE_RATE=0.1
FAPILOG_FASTAPI__LOG_ERRORS_ON_SKIP=true

Environment variables take priority over code-specified values. When an override occurs, a warning is emitted via internal diagnostics:

Config override: sample_rate=1.0 overridden by FAPILOG_FASTAPI__SAMPLE_RATE=0.1

Deprecation timeline

v0.14.0: setup_logging() emits DeprecationWarning
v0.15.0 (planned): setup_logging() will be removed

Need help?

If you encounter issues during migration, please open an issue.