Configure Logging to File in Phoenix

config.exs

# Configures Elixir's Logger to log to file
# ensure https://github.com/onkel-dirtus/logger_file_backend 
# is installed in deps of the project in mix.exs
# reuses the original phoenix logging format.
config :logger, backends: [{LoggerFileBackend, :request_log}],
  format: "$time $metadata[$level] $message\n",
  metadata: [:request_id]

# Keep a seperate log file for each env.
# logs are stored in the root directory of the application
# inside the logs folder. 
# Note: Remember to specify the format along with the metadata required.
# Configurable per LoggerFileBackend.
config :logger, :request_log,
  path: "logs/request.#{Mix.env}.log",
  format: "$time $metadata[$level] $message\n",
  metadata: [:request_id]