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Elixir logging to (multiple) file(s) using metadata_filter
This is a follow up post for JSON Logging in Elixir using a custom formatter where we looked in to how to log request logs to a file using a custom formatter. We require below hex dependencies in our project to log request logs and other app logs.
{:plug_logger_json, "~> 0.7.0"},
{:logger_file_backend, "~> 0.0.12"}
Unlike non functional languages where you have log objects per log file and can use them to write to different log
require "logger"
request_logger = Logger.new('/src/obliviator/log/obliviator_request.log')
request_logger.debug("I'm a request debug log")
stream_logger = Logger.new('/src/obliviator/log/stream.log')
stream_logger.info("I'm a stream info log")
but in Elixir you only have a Logger object and need to differentiate based on metadata assigned to write to the associated log. metadata_filter can be assigned on multiple fields. We can separate logs by each application running on our VM or by key identifying our file.
# log by identifying application
metadata_filter: [application: :plug_logger_json]
#log by tagging log by key value
metadata_filter: [log: :stream]
The full config would be as below
use Mix.Config
config :plug_logger_json,
filtered_keys: ["password", "authorization"],
suppressed_keys: ["api_version", "log_type"]
config :logger,
backends: [
{LoggerFileBackend, :request_log},
{LoggerFileBackend, :message_log},
{LoggerFileBackend, :debugging_log}
],
utc_log: true,
handle_otp_reports: true
# configuration for the {LoggerFileBackend, :request_log} backend
config :logger, :request_log,
format: {Obliviator.Formatter.RequestLog, :format},
metadata: :all,
path: "/src/obliviator/log/obliviator_request.log",
level: :info,
metadata_filter: [application: :plug_logger_json]
config :logger, :message_log,
format: {Obliviator.Formatter.MessageLog, :format},
metadata: :all,
path: "/src/obliviator/log/stream.log",
level: :info,
metadata_filter: [log: :stream]
config :logger, :debugging_log,
format: {Obliviator.Formatter.MessageLog, :format},
metadata: :all,
path: "/src/obliviator/log/obliviator_debugging.log",
level: :debug,
metadata_filter: [log: :debugging]
Once the config is in place data can be logged as follows
# log to :stream
Logger.info("Stream msg", log: :stream)
#log to :debugging
Logger.debug("Debugging", log: :debugging)
Elixir logging might look limiting at the start but with a powerful custom formatter and metadata filtering ability its is sufficiently better than many ;)
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