Steno

Steno is a lightweight, modular logging library written specifically to support Cloud Foundry.

Concepts

Steno is composed of three main classes: loggers, sinks, and formatters. Loggers are the main entry point for Steno. They consume user input, create structured records, and forward said records to the configured sinks. Sinks are the ultimate destination for log records. They transform a structured record into a string via a formatter and then typically write the transformed string to another transport.

Configuration

To use steno, you must configure one or more 'sinks', a 'codec' and a 'context'. If you don't provide a codec, steno will encode your logs as JSON.

For example:

config = Steno::Config.new(
  :sinks   => [Steno::Sink::IO.new(STDOUT)],
  :codec   => Steno::Codec::Json.new,
  :context => Steno::Context::ThreadLocal.new)

from YAML file

Alternatively, Steno can read its configuration from a YAML file in the following format:

# config.yml
---
logging:
  file: /some/path            # Optional - path a log file
  max_retries: 3              # Optional - number of times to retry if a file write fails.
  syslog: some_syslog.id      # Optional - only works on *nix systems
  eventlog: true              # Optional - only works on Windows
  fluentd:                    # Optional
    host: fluentd.host
    port: 9999
  level: debug                # Optional - Minimum log level that will be written.
                              # Defaults to 'info'

Then, in your code:

config = Steno::Config.from_file("path/to/config.yml")

With this configuration method, if neither file, syslog or fluentd are provided, steno will use its stdout as its sink. Also, note that the top-level field logging is required.

from Hash

As a third option, steno can be configured using a hash with the same structure as the above YAML file (without the top-level logging key):

config = Steno::Config.from_hash(config_hash)

Usage

Steno.init(config)
logger = Steno.logger("test")  
logger.info("Hello world!")

Log levels

LEVEL	NUMERIC RANKING 
off		0
fatal	1
error	5
warn	10
info	15
debug	16
debug1	17
debug2	18
all		30