Append request and response data to a log file on disk.

It is not recommended to use this plugin in production, it would be better to use another logging plugin, for example syslog, in those cases. Due to system limitations this plugin uses blocking file i/o, which will hurt performance, and hence is an anti-pattern for Kong installations.


Configuring the plugin is straightforward, you can add it on top of an API (or Consumer) by executing the following request on your Kong server:

$ curl -X POST http://kong:8001/apis/{api}/plugins \
    --data "name=file-log" \
    --data "config.path=/tmp/file.log"

api: The id or name of the API that this plugin configuration will target

You can also apply it for every API using the http://kong:8001/plugins/ endpoint. Read the Plugin Reference for more information.

form parameter default description
name The name of the plugin to use, in this case: file-log
The CONSUMER ID that this plugin configuration will target. This value can only be used if authentication has been enabled so that the system can identify the user making the request.
config.path The file path of the output log file. The plugin will create the file if it doesn't exist yet. Make sure Kong has write permissions to this file.
reopen false Introduced in Kong 0.10.2. Determines whether the log file is closed and reopened on every request. If the file is not reopened, and has been removed/rotated, the plugin will keep writing to the stale file descriptor, and hence lose information.

Log Format

Every request will be logged separately in a JSON object separated by a new line \n, with the following format:

    "request": {
        "method": "GET",
        "uri": "/get",
        "url": "",
        "size": "75",
        "querystring": {},
        "headers": {
            "accept": "*/*",
            "host": "",
            "user-agent": "curl/7.37.1"
    "upstream_uri": "/",
    "response": {
        "status": 200,
        "size": "434",
        "headers": {
            "Content-Length": "197",
            "via": "kong/0.3.0",
            "Connection": "close",
            "access-control-allow-credentials": "true",
            "Content-Type": "application/json",
            "server": "nginx",
            "access-control-allow-origin": "*"
    "tries": [
            "state": "next",
            "code": 502,
            "ip": "",
            "port": 8000
            "ip": "",
            "port": 8000
    "authenticated_entity": {
        "consumer_id": "80f74eef-31b8-45d5-c525-ae532297ea8e",
        "id": "eaa330c0-4cff-47f5-c79e-b2e4f355207e"
    "api": {
        "created_at": 1488830759000,
        "hosts": [
        "http_if_terminated": true,
        "https_only": false,
        "id": "6378122c-a0a1-438d-a5c6-efabae9fb969",
        "name": "example-api",
        "preserve_host": false,
        "retries": 5,
        "strip_uri": true,
        "upstream_connect_timeout": 60000,
        "upstream_read_timeout": 60000,
        "upstream_send_timeout": 60000,
        "upstream_url": ""
    "consumer": {
        "username": "demo",
        "created_at": 1491847011000,
        "id": "35b03bfc-7a5b-4a23-a594-aa350c585fa8"
    "latencies": {
        "proxy": 1430,
        "kong": 9,
        "request": 1921
    "client_ip": "",
    "started_at": 1433209822425

A few considerations on the above JSON object:

  • request contains properties about the request sent by the client
  • response contains properties about the response sent to the client
  • tries contains the list of (re)tries (successes and failures) made by the load balancer for this request
  • api contains Kong properties about the specific API requested
  • authenticated_entity contains Kong properties about the authenticated credential (if an authentication plugin has been enabled)
  • consumer contains the authenticated Consumer (if an authentication plugin has been enabled)
  • latencies contains some data about the latencies involved:
    • proxy is the time it took for the final service to process the request
    • kong is the internal Kong latency that it took to run all the plugins
    • request is the time elapsed between the first bytes were read from the client and after the last bytes were sent to the client. Useful for detecting slow clients.
  • client_ip contains the original client IP address
  • started_at contains the UTC timestamp of when the API transaction has started to be processed.

Kong Process Errors

This logging plugin will only log HTTP request and response data. If you are looking for the Kong process error file (which is the nginx error file), then you can find it at the following path: {prefix}/logs/error.log

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