# Logster
[](https://github.com/navinpeiris/logster/actions/workflows/ci.yml)
[](https://hex.pm/packages/logster)
[](https://hex.pm/packages/logster)
[](http://doge.mit-license.org)
> **Note**\
> This is the documentation for v2 of Logster. If you're looking for v1, see the [v1 branch](https://github.com/navinpeiris/logster/tree/v1.x).
An easy-to-parse, single-line logger for Elixir Phoenix and Plug applications. Supports logfmt, JSON and custom formatting.
## Motivation
By default, the Phoenix log output for a request looks like:
```text
[info] GET /articles/some-article
[debug] Processing with HelloPhoenix.ArticleController.show/2
Parameters: %{"id" => "some-article"}
Pipelines: [:browser]
[info] Sent 200 in 21ms
```
This can be handy for development, but cumbersome in production. The log output is spread across multiple lines making it difficult to parse and search.
Logster aims to solve this problem by logging the request in a easy-to-parse single line like:
```text
[info] state=sent method=GET path=/articles/some-article format=html controller=HelloPhoenix.ArticleController action=show params={"id":"some-article"} status=200 duration=0.402
```
This is especially handy when integrating with log management services such as [Better Stack](https://betterstack.com/telemetry) or [Papertrail](https://papertrailapp.com/).
Alternatively, Logster can also output JSON formatted logs (see configuration section below), or you can provide a custom formatter:
```text
[info] {"state":"sent","method":"GET","path":"/articles/some-article","format":"html","controller":"HelloPhoenix.ArticleController","action":"show","params":{"id":"some-article"},"status":200,"duration":0.402}
```
## Migrating from v1.x to v2.x
See [Migration Guide](MIGRATION_GUIDE.md) for more information on migrating from v1.x to v2.x.
## Installation
Add `:logster` to the list of dependencies in `mix.exs`:
```elixir
def deps do
[{:logster, "~> 2.0.0-rc.1"}]
end
```
## Usage
### Using with Phoenix
Attach the Logster Phoenix logger in the `start` function in your project's `application.ex` file:
```elixir
# lib/my_app/application.ex
def start(_type, _args) do
children = [
# ...
]
#
# Add the line below:
#
:ok = Logster.attach_phoenix_logger()
opts = [strategy: :one_for_one, name: MyApp.Supervisor]
Supervisor.start_link(children, opts)
end
```
Next, disable the default Phoenix logger by adding the following line to your `config.exs` file:
```elixir
# config/config.exs
config :phoenix, :logger, false
```
### Using with Plug
Add `Logster.Plug` to your plug pipeline, or in the relevant module:
```elixir
plug Logster.Plug
```
### Using the standalone logger
Logster provides `debug`, `info`, `warning`, `error` etc convenience functions that mimic those provided by the elixir logger, which outputs messages in your chosen log format.
For example:
```elixir
Logster.info(service: :payments, event: :received, amount: 1000, customer: 123)
```
will output the following:
```
[info] service=payments event=received amount=1000 customer=123
```
You can also provide a function to be called lazily, which will only be called if the log level is enabled:
```elixir
Logster.debug(fn ->
# some potentially expensive operation
# won't be called if the log level is not enabled
customer = get_customer_id()
[service: :payments, event: :received, amount: 1000, customer: customer]
end)
```
## Configuration
### Application wide
You can configure Logster application wide using your `config.exs`, or environment specific config file by providing options like:
```elixir
config :logster,
formatter: :json,
headers: ["content-type"],
excludes: [:params]
```
### Per request
You can then customize each option on a request basis by passing them as options to the `Logster.ChangeConfig` plug in the relevant controller or plug:
```elixir
plug Logster.ChangeConfig, status_2xx_level: :debug, headers: ["content-type", "x-request-id"]
```
or, for specific actions in the controller:
```elixir
plug Logster.ChangeConfig, [status_2xx_level: :debug, headers: ["content-type", "x-request-id"]] when action in [:index, :show]
```
This is specially useful for cases such as when you want to lower the log level for a healthcheck endpoint that gets hit every few seconds.
### Plug level
If you're using the `Logster.Plug` plug, you can also pass options to it directly:
```elixir
plug Logster.Plug, status_2xx_level: :debug, headers: ["content-type", "x-request-id"]
```
## Configuration options
### Formatter
#### JSON formatter
```elixir
config :logster, formatter: :json
```
_Caution:_ There is no guarantee that what reaches your console will be valid JSON. The Elixir `Logger` module has its own formatting which may be appended to your message. See the [Logger documentation](http://elixir-lang.org/docs/stable/logger/Logger.html) for more information.
#### Custom formatter
Provide a function that takes one argument, the parameters as input, and returns formatted output
```elixir
config :logster, formatter: &MyCustomFormatter.format/1
```
### Log level per status group
You can change the log level for each status group by using the following configuration options:
```elixir
config :logster,
status_2xx_level: :debug, # default: :info
status_3xx_level: :debug, # default: :info
status_4xx_level: :info, # default: :warning
status_5xx_level: :error # default: :error
```
### Fine grained log level configuration
You can specify a function to be called to determine the log level for each request.
This function will be called with the `conn`, and expects a logger level, or `false` to not log the request as return value.
```elixir
# config/config.exs
config :logster, log: {MyLoggingModule, :log_level, []}
```
```elixir
defmodule MyLoggingModule do
def log_level(%{status: status}) when status >= 500, do: :error
def log_level(%{status: status}) when status >= 400, do: :warning
def log_level(%{path_info: ["status" | _]}), do: false
def log_level(_), do: :info
end
```
### Request headers
By default, Logster won't log any request headers. To log specific headers, you can use the `:headers` option:
```elixir
config :logster, headers: ["my-header-one", "my-header-two"]
```
### Enabling extra fields
One or more of the following fields can be optionally enabled through the `extra_fields` configuration option:
- host
- query_params
Example:
```elixir
config :logster, extra_fields: [:host, :query_params]
```
### Excluding fields
You can exclude fields with `:excludes`:
```elixir
config :logster, excludes: [:params, :status, :state]
```
Example output:
```
[info] method=GET path=/articles/some-article format=html controller=HelloPhoenix.ArticleController action=show duration=0.402
```
### Renaming default fields
You can rename the default keys passing a keyword list like:
```elixir
config :logster, renames: [duration: :response_time, params: :parameters]
```
Example output:
```
[info] method=GET path=/articles/some-article format=html controller=HelloPhoenix.ArticleController action=show parameters={"id":"some-article"} status=200 response_time=0.402 state=set
```
### Filtering parameters
By default, Logster filters parameters named `password`.
To change the filtered parameters:
```elixir
config :logster, filter_parameters: ["password", "secret", "token"]
```
### Metadata
Custom metadata can be added to logs using `Logger.metadata` and configuring your logger backend:
```elixir
# add metadata for all future logs from this process
Logger.metadata(%{user_id: "123", foo: "bar"})
# example for configuring console backend to include metadata in logs.
# see https://hexdocs.pm/logger/Logger.html#module-console-backend documentation for more
# config.exs
config :logger, :console, metadata: [:user_id, :foo]
```
The easiest way to do this app wide is to introduce a new plug which you can include in your Phoenix router pipeline.
For example:
```elixir
defmodule HelloPhoenix.SetLoggerMetadata do
def init(opts), do: opts
def call(conn, _opts) do
Logger.metadata user_id: get_user_id(conn),
remote_ip: format_ip(conn)
conn
end
defp format_ip(%{remote_ip: remote_ip}) when remote_ip != nil, do: :inet_parse.ntoa(remote_ip)
defp format_ip(_), do: nil
defp get_user_id(%{assigns: %{current_user: %{id: id}}}), do: id
defp get_user_id(_), do: nil
end
```
And then add this plug to the relevant pipelines in the router:
```elixir
pipeline :browser do
plug :fetch_session
plug :fetch_flash
plug :put_secure_browser_headers
# ...
plug HelloPhoenix.SetLoggerMetadata
# ...
end
```
## Development
Use the following mix task before pushing commits to run the same checks that are run in CI:
```
mix ci
```
## Acknowledgements
This library was inspired by the ruby [lograge](https://github.com/roidrage/lograge) gem.
## License
The MIT License
Copyright (c) 2016-present Navin Peiris
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
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copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
