How do you configure Uvicorn logging and access logs?

Uvicorn uses Python's standard logging module with configurable log levels and optional access logging. Log configuration can be provided via CLI flags, environment variables, or a config file.

# Log level options: critical, error, warning, info (default), debug, trace
uvicorn main:app --log-level debug

# Disable access log (reduces CPU by ~10% under high load)
uvicorn main:app --no-access-log

# Disable colour in logs (useful for log aggregators)
uvicorn main:app --no-use-colors

# Use a custom logging config file (JSON, YAML, or INI)
uvicorn main:app --log-config logging.yaml

# Programmatic log config:
uvicorn.run("main:app", log_level="warning", access_log=False)

# Production hardened logging:
uvicorn main:app \
    --log-level warning \
    --no-access-log \
    --no-use-colors

# logging.yaml - custom Uvicorn log config
version: 1
formatters:
  default:
    format: "%(asctime)s %(levelname)s %(message)s"
    use_colors: false
  access:
    format: '%(asctime)s %(client_addr)s - "%(request_line)s" %(status_code)s'
handlers:
  default:
    class: logging.StreamHandler
    formatter: default
  access:
    class: logging.StreamHandler
    formatter: access
loggers:
  uvicorn:
    handlers: [default]
    level: INFO
  uvicorn.access:
    handlers: [access]
    level: INFO
    propagate: false

Performance tip: disabling access logs (--no-access-log) and setting --log-level warning can reduce CPU usage by up to 10-15% under high concurrency, since log formatting and I/O for every request is eliminated. In production, access logging is often handled at the reverse proxy layer (Nginx/Caddy) instead.

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