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HTTP Logger Integration in KrakenD API Gateway

Document updated on Jan 24, 2022

The HTTP logger is a response dumper that allows you to write the backend request and its response into a file, to help you debug your processes during development.

A development tool

Although it works, we discourage you from using this plugin in production for the following reasons:

  1. Performance: The throughput of the filesystem is usually slower than the network. This plugin writes two files on the disk for each request (consuming your disk space and I/O).
  2. Privacy: Your backend responses are saved as they are in a plain file. If you have sensitive data, you might breach your company policies.

Response logging configuration

The response dumper is an HTTP-client plugin, and you need to load it in the backend section. Notice the different elements you need to include in the configuration:

    "version": 3,
    "plugin": {
        "pattern": ".so",
        "folder": "/opt/krakend/plugins/"
    "endpoints": [
            "endpoint": "/health",
            "output_encoding": "no-op",
            "backend": [
                    "url_pattern": "/__health",
                    "host": ["http://localhost:8080"],
                    "encoding": "no-op",
                    "extra_config": {
                        "plugin/http-client": {
                            "name": "http-logger",
                            "path": "./dumps",
                            "file_prefix": "health"

The configuration flags relative to the plugin are:

  • path (string): The folder where to dump the responses. The folder destination must exist and be writeable by the krakend user (or any other user you have chosen to start the process). Otherwise, the plugin will fail to save the dumps. So in the example above, a mkdir -p dumps is needed to make the plugin work correctly.
  • file_prefix (string): As all files will use in the name the timestamp to avoid concurrency problems, you can add a prefix to identify which backend wrote that response.

Dump file format

For each request to KrakenD, two files are written in the directory with the following naming convention:

  • ${file_prefix}_request_${timestamp}.txt
  • ${file_prefix}_response_${timestamp}.txt

Each file contains the request and the response respectively using the HTTP format, as if you did a curl -i which contains the headers and the body. So for the example above, you would have:

Request to your backend (e.g: health_request_1649753368.txt)

GET /__health HTTP/1.1
Host: localhost:8082
User-Agent: KrakenD Version 2.0.0
X-Forwarded-Host: localhost:8082
Accept-Encoding: gzip

Response from your backend (e.g: health_response_1649753368.txt):

HTTP/1.1 200 OK
Content-Length: 92
Content-Type: application/json; charset=utf-8
Date: Tue, 12 Apr 2022 08:49:28 GMT

{"agents":{},"now":"2022-04-12 10:49:28.90471549 +0200 CEST m=+428.707781074","status":"ok"}

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