LoggerEtsBackend

A simple Logger backend which writes log entries to an ETS table. It does not create or manage the table for you; you must do this external to the logging app.

LoggerEtsBackend borrows heavily from LoggerFileBackend, and therefore acts much the same way.

Rationale

The primary use-case for this backend is not for persistent logs, but for temporary logs that may need to be inspected at run-time by the system itself. By pushing log messages to an ETS table, data can be quickly searched using match_specs based on message contents or the metadata stored along with the entry.

Configuration

LoggerEtsBackend is a custom backend for the elixir :logger application. This backend can only log to a single ETS table, so there must be one :logger backend configured for each log file we need. Each backend has a name like {LoggerEtsBackend, id}, where id is any elixir term (usually an atom).

Note: tables use for logging are recommented to be configured with the :ordered_set and :public options.

Configuration Example

config :logger,
  backends: [{LoggerEtsBackend, :inspection_log}]

# configuration for the {LoggerEtsBackend, :critical_log} backend
config :logger, :critical_log,
  table: :critical_table,
  level: :error

Usage

LoggerEtsBackend supports the following configuration values:

• table - the table name to push log tuples to
• level - the logging level for the backend
• metadata - the metadata to include
• metadata_filter - metadata terms which must be present in order to log

Note: It is recommended that metadata_filter is set for this backend, to ensure only a small subset of log entries are captured.

Examples

Runtime configuration

# some process starts an ets table
:ets.new(:debug_messages, [:ordered_set, :public, :named_table])
...
Logger.add_backend {LoggerFileBackend, :debug}
Logger.configure_backend {LoggerFileBackend, :debug},
  table: :debug_messages,
  metadata: ...,
  metadata_filter: ...

Application config for multiple log files

config :logger,
  backends: [{LoggerEtsBackend, :info},
             {LoggerEtsBackend, :error}]

config :logger, :info,
  table: :info_messages,
  level: :info

config :logger, :error,
  table: :error_messages,
  level: :error

Filter out metadata

This example removes all the default metadata and only keeps the :module name which issued the log message.

config :logger,
  backends: [{LoggerEtsBackend, :info}]

config :logger, :info,
  table: :info_messages,
  level: :info,
  metadata: [application: :ui]

Filtering logging by specifying metadata terms

This example only logs :info statements originating from the :ui OTP app. The :application metadata key is auto-populated by Logger.

config :logger,
  backends: [{LoggerEtsBackend, :ui}]

config :logger, :ui,
  table: :ui_messages,
  level: :info,
  metadata_filter: [application: :ui]