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Logging - Syslog, stdout and GELF

Document updated on Jan 30, 2019

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.

Extending the logging capabilities

Different logging components allow you to extend the logging functionality, such as sending the events to the syslog, 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)

Improved logging with gologging.

The component gologging 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

Enabling gologging

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": 2,
  "extra_config": {
    "github_com/devopsfaith/krakend-gologging": {
      "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:

  • INFO

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
  • logstash
  • custom

If you select the custom format, you’ll be able to use the custom_format field:

  • "custom_format": "%{message}"

The pattern to use is the same as the go-logging library


If you want to log using the Logstash standard via stdout, you have to add the krakend-logstash integration in the root level of your krakend.json, inside the extra_config section. The gologging needs to be enabled too (but the format should be default).

For instance:

"extra_config": {
  "github_com/devopsfaith/krakend-logstash": {
    "enabled": true
  "github_com/devopsfaith/krakend-gologging": {
    "level": "INFO",
    "prefix": "[KRAKEND]",
    "syslog": false,
    "stdout": true

Unresolved issues?

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