Improved Logging - Syslog, stdout

Document updated on Jun 15, 2022

By default, when KrakenD starts all the log events are sent to the standard output using the basic logger capabilities of the Lura Project. The reporting level, in that case, is DEBUG and adds no prefix to the log lines.

There are two types of logs:

• Access logs (activity from users)
• Application logs (errors, debugging information and other application messages)

Access logs

The access log shows with the following format:

[GIN] 2022/06/15 - 15:38:58 | 200 |       4.529µs |      172.17.0.1 | GET      "/test/foo"
[GIN] 2022/06/15 - 15:38:59 | 200 |       3.647µs |      172.17.0.1 | GET      "/test/bar"

The access log is not customizable, but it can be disabled using disable_access_log (see how to remove requests from logs options).

Application logs

Different logging components allow you to extend the application logging functionality, such as sending the events to the syslog, use JSON format, choosing the verbosity level, or use the Graylog Extended Log Format (GELF).

In addition to this, a lot of exporters are available to send your logs out (see Telemetry)

The component telemetry/logging extends the default logging capabilities with the following capabilities:

• Option to write to the stdout
• Option to write to the syslog
• Add a prefix to log lines
• Select the reporting level
• Option to use a predefined or custom format

To enjoy the extended logging capabilities the component needs to be added in the krakend.json configuration. Add its namespace in the extra_config at the root level:

{
  "version": 3,
  "extra_config": {
    "telemetry/logging": {
      "level": "INFO",
      "prefix": "[KRAKEND]",
      "syslog": true,
      "stdout": true,
      "format": "custom",
      "custom_format": "%{message}"
    }
  }
}

The snippet above shows the four options you can configure, explained below.

Set the reporting level

Define the severity you would like to see in the logs with level. The recognized options from more to less verbosity are:

• DEBUG
• INFO
• WARNING
• ERROR
• CRITICAL

Write to Syslog or Stdout

For each log event triggered, the output can write to the syslog, the stdout, or both. The accepted values are a boolean. When true, the log writes in the selected target:

• "syslog": true
• "stdout": true

Add a prefix to all lines

Besides, you might want to choose to add a string to every logged line, so you can quickly filter messages with external tools later.

• "prefix": "[ANY STRING]"

Predefined and customs formats

If you want to follow other patterns for logging, you’re able to.

• "format": "custom"

The valid formats are:

• default uses the pattern %{time:2006/01/02 - 15:04:05.000} %{color}▶ %{level:.6s}%{color:reset} %{message}
• logstash uses the pattern {"@timestamp":"%{time:2006-01-02T15:04:05.000+00:00}", "@version": 1, "level": "%{level}", "message": "%{message}", "module": "%{module}"}. See Logstash
• custom lets you write your own pattern, e.g: %{message}

To know more about the possible pattern format see the go-logging library

Log in JSON format

If you want to log in the stdout using JSON format see Logstash