https://github.com/jonathanperret/logger_lager_backend

A Logger backend that forwards messages to lager
https://github.com/jonathanperret/logger_lager_backend

elixir lager logging

Last synced: 3 months ago
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A Logger backend that forwards messages to lager

• Host: GitHub
• URL: https://github.com/jonathanperret/logger_lager_backend
• Owner: jonathanperret
• License: mit
• Created: 2016-04-05T16:55:35.000Z (almost 9 years ago)
• Default Branch: master
• Last Pushed: 2021-08-02T15:59:28.000Z (over 3 years ago)
• Last Synced: 2024-10-18T10:27:03.731Z (4 months ago)
• Topics: elixir, lager, logging
• Language: Elixir
• Homepage:
• Size: 15.6 KB
• Stars: 12
• Watchers: 4
• Forks: 6
• Open Issues: 3
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# LoggerLagerBackend

A `lager` (https://github.com/erlang-lager/lager) backend for Elixir's `Logger`

(https://hexdocs.pm/logger/Logger.html).

That is, it routes messages generated with `Logger.()` to `lager`. This

is useful if you have a mixed Erlang/Elixir project and have decided to

standardize on `lager` as a logging framework.

Known limitations:

* You're on your own to configure and start `lager`.

* Only `lager`'s default sink (`:lager_event`) is used.

* Performance is probably not ideal - all messages received are sent to `lager`

  regardless of the configured level and `lager`'s compile-time optimization

  does not happen. However, `Logger` will still do its own optimization

  upstream of this backend.

* Metadata is passed straight from `Logger` to `lager`, hoping that the keys

  match. It seems to be the case for the basics (`module`, `function`...) but

  may need looking into.

## Installation

Add `logger_lager_backend` to your list of dependencies in `mix.exs`:

```elixir

def deps do

  [{:logger_lager_backend, "~> 0.1.0"}]

end

```

## Configuration

Instruct `Logger` to use `logger_lager_backend`:

```elixir

config :logger,

  backends: [LoggerLagerBackend],

  handle_otp_reports: false,

  level: :debug

```

This sends all messages of level `debug` or higher to `lager`. They will then

be subject to filtering and routing according to whichever `lager` config you

have in place.

We also use `handle_otp_reports: false` to avoid having messages from the

Erlang's built-in `error_logger` module appear twice in the output.

## Troubleshooting

### `FORMAT ERROR`s in log

If you get `FORMAT ERROR` messages like this one:

```text

FORMAT ERROR: "~s" [[<<"GenServer :redis_sub_0_8 terminating">>,<<"\n** (stop) ">>|<<":redis_down">>]

```

You're probably hitting [erlang-lager/lager#326](https://github.com/erlang-lager/lager/issues/326). Upgrade

`lager` to `3.2.0` or more recent.

### `Elixir.Logger.Supervisor` error on startup

If you get the following message on startup:

```text

[error] Supervisor 'Elixir.Logger.Supervisor' had child 'Elixir.Logger.ErrorHandler' started with

  'Elixir.Logger.Watcher':watcher(error_logger, 'Elixir.Logger.ErrorHandler',

  {true,false,500}, link) at <0.422.0> exit with reason normal in context child_terminated

```

Make sure the `:lager` application is started before `:logger`, by putting

`:lager` first in your `applications` list in `mix.exs`:

```elixir

def application do

  [applications: [:lager, :logger, …],

   mod: {MyApp, []}]

end

```

## Related projects

* [lager_logger](https://github.com/PSPDFKit-labs/lager_logger) does the

  opposite of this backend: it sends `lager` messages to `Logger`.

* [exlager](https://github.com/khia/exlager) offers an Elixir frontend to

  `lager`, which can be an alternative to this backend if you control all the

  code that does logging. But if you are using e.g. `Ecto`, which writes to

  `Logger`, `exlager` will not help you.