Logging Rails apps with Logtail

To help you get started with using Logtail in your Rails projects, here is an overview of how to use the Logtail logger in your Rails apps.

Setup

Setting up the integration is very easy. All you need is a source-token that you'll get after you create a Source in your logtail.com account. Then run the following command to create the default config file:

bundle exec rake logtail:install source_token=YOUR_LOGTAIL_SOURCE_TOKEN
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Donā€™t forget to replace YOUR_LOGTAIL_SOURCE_TOKEN with your actual source token which you can find in the source settings. This will generate config/initializers/logtail.rb.

Logging example

To send logs to Logtail use the Rails.logger logger. It provides 5 logging methods for the 5 default log levels. The log levels and their method are:

  • DEBUGĀ - Send debug messages using theĀ debug()Ā method
  • INFOĀ - Send informative messages about the application progress using theĀ info()Ā method
  • WARNĀ - Report non-critical issues using theĀ warn()Ā method
  • ERRORĀ - Send messages about serious problems using theĀ error()Ā method
  • FATAL - Send messages about fatal events that caused the app to crash using the fatal() method

In this example, we will send two logs - DEBUG and INFO:

# Send debug logs messages using the debug() method
Rails.logger.debug("Logtail is ready!")

# Send informative messages about interesting events using the info() method
Rails.logger.info("I am using Logtail!")
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This will create the following output:

{
    "dt": "2021-03-29T11:24:54.788Z",
    "level": "debug",
    "message": "Logtail is ready!",
    "context": {
        "runtime": {
            "thread_id": 123,
            "file": "main.rb",
            "line": 6,
            "frame": null,
            "frame_label": "<main>"
        },
        "system": {
            "hostname": "hostname"
            "pid": 1234
        }
    }
}

{
    "dt": "2021-03-29T11:24:54.788Z",
    "level": "info",
    "message": "I am using Logtail!",
    "context": {
        "runtime": {
            "thread_id": 123,
            "file": "main.rb",
            "line": 6,
            "frame": null,
            "frame_label": "<main>"
        },
        "system": {
            "hostname": "hostname"
            "pid": 1234
        }
    }
}
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Logging structured data

You can also log additional structured data. This can help you provide additional information when debugging and troubleshooting your application. You can provide this data as the second argument to any logging method.

# Send messages about worrying events using the warn() method
# You can also log additional structured data
Rails.logger.warn(
    "log structured data",
    item: {
        url: "https://fictional-store.com/item-123",
        price: 100.00
    }
)
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This will create the following output:

{
    "dt": "2021-03-29T11:24:54.788Z",
    "level": "warn",
    "message": "log structured data",
    "item": {
        "url": "https://fictional-store.com/item-123",
        "price": 100.00
    },
    "context": {
        "runtime": {
            "thread_id": 123,
            "file": "main.rb",
            "line": 7,            
            "frame": null,
            "frame_label": "<main>"
        },
        "system": {
            "hostname": "hostname"
            "pid": 1234
        }
    }
}
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Adding more context to your logs

We add information about the current runtime environment and the current process into a context field of the logged item by default.

If you want to add custom information to all logged items (e.g., the ID of the current user), you can do so by adding a custom context:

# Provide context to the logs
Logtail.with_context(user: { id: 123 }) do
    Rails.logger.info('new subscription')
end
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This will generate the following JSON output:

{
    "dt": "2021-03-29T11:24:54.788Z",
    "level": "warn",
    "message": "new subscription",
    "context": {
        "runtime": {
            "thread_id": 123456,
            "file": "main.rb",
            "line": 2,            
            "frame": null,
            "frame_label": "<main>"
        },
        "system": {
            "hostname": "hostname"
            "pid": 1234
        },
        "user": {
            "id": 123
        }
    }
}
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We will automatically add the information about the current user to each log if you're using Ruby on Rails and the Devise gem.

If you're not using Devise or you want to log some additional information for every request your Rails app handles, you can easily implement this using Rails' around_action in your application controller. A simple implementation could look like this:

class ApplicationController < ActionController::Base
  around_action :with_logtail_context

  private

    def with_logtail_context
      if user_signed_in?
        Logtail.with_context(user_context) { yield }
      else
        yield
      end
    end

    def user_context
      Logtail::Contexts::User.new(
        id: current_user.id,
        name: current_user.name,
        email: current_user.email
      )
    end
end
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