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File Log

By Kong Inc.
You are browsing documentation for an outdated plugin version.

Looking for the plugin's configuration parameters? You can find them in the File Log configuration reference doc.

Append request and response data in JSON format to a log file. You can also specify streams (for example, /dev/stdout and /dev/stderr), which is especially useful when running Kong in Kubernetes.

This plugin uses blocking I/O, which could affect performance when writing to physical files on slow (spinning) disks.

Log format

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

{
    "response": {
        "size": 9982,
        "headers": {
            "access-control-allow-origin": "*",
            "content-length": "9593",
            "date": "Thu, 19 Sep 2024 22:10:39 GMT",
            "content-type": "text/html; charset=utf-8",
            "via": "1.1 kong/3.8.0.0-enterprise-edition",
            "connection": "close",
            "server": "gunicorn/19.9.0",
            "access-control-allow-credentials": "true",
            "x-kong-upstream-latency": "171",
            "x-kong-proxy-latency": "1",
            "x-kong-request-id": "2f6946328ffc4946b8c9120704a4a155"
        },
        "status": 200
    },
    "route": {
        "updated_at": 1726782477,
        "tags": [],
        "response_buffering": true,
        "path_handling": "v0",
        "protocols": [
            "http",
            "https"
        ],
        "service": {
            "id": "fb4eecf8-dec2-40ef-b779-16de7e2384c7"
        },
        "https_redirect_status_code": 426,
        "regex_priority": 0,
        "name": "example_route",
        "id": "0f1a4101-3327-4274-b1e4-484a4ab0c030",
        "strip_path": true,
        "preserve_host": false,
        "created_at": 1726782477,
        "request_buffering": true,
        "ws_id": "f381e34e-5c25-4e65-b91b-3c0a86cfc393",
        "paths": [
            "/example-route"
        ]
    },
    "workspace": "f381e34e-5c25-4e65-b91b-3c0a86cfc393",
    "workspace_name": "default",
    "tries": [
        {
            "balancer_start": 1726783839539,
            "balancer_start_ns": 1.7267838395395e+18,
            "ip": "34.237.204.224",
            "balancer_latency": 0,
            "port": 80,
            "balancer_latency_ns": 27904
        }
    ],
    "client_ip": "192.168.65.1",
    "request": {
        "id": "2f6946328ffc4946b8c9120704a4a155",
        "headers": {
            "accept": "*/*",
            "user-agent": "HTTPie/3.2.3",
            "host": "localhost:8000",
            "connection": "keep-alive",
            "accept-encoding": "gzip, deflate"
        },
        "uri": "/example-route",
        "size": 139,
        "method": "GET",
        "querystring": {},
        "url": "http://localhost:8000/example-route"
    },
    "upstream_uri": "/",
    "started_at": 1726783839538,
    "source": "upstream",
    "upstream_status": "200",
    "latencies": {
        "kong": 1,
        "proxy": 171,
        "request": 173,
        "receive": 1
    },
    "service": {
        "write_timeout": 60000,
        "read_timeout": 60000,
        "updated_at": 1726782459,
        "host": "httpbin.konghq.com",
        "name": "example_service",
        "id": "fb4eecf8-dec2-40ef-b779-16de7e2384c7",
        "port": 80,
        "enabled": true,
        "created_at": 1726782459,
        "protocol": "http",
        "ws_id": "f381e34e-5c25-4e65-b91b-3c0a86cfc393",
        "connect_timeout": 60000,
        "retries": 5
    }
}

Log format definitions

  • service: Properties about the service associated with the requested route.
  • route: Properties about the specific route requested.
  • request: Properties about the request sent by the client.
  • response: Properties about the response sent to the client.
  • latencies: Latency data.
    • kong: The internal Kong Gateway latency, in milliseconds, that it takes to process the request.
      • For requests that are proxied to an upstream, it is equivalent to the X-Kong-Proxy-Latency response header.
      • For requests that generate a response within Kong Gateway (typically the result of an error or a plugin-generated response), it is equivalent to the X-Kong-Response-Latency response header.
    • request: The time in milliseconds that has elapsed between when the first bytes were read from the client and the last byte was sent to the client. This is useful for detecting slow clients.
    • proxy: The time in milliseconds that it took for the upstream to process the request. In other words, it’s the time elapsed between transferring the request to the final service and when Kong Gateway starts receiving the response.
    • receive: The time in milliseconds that it took to receive and process the response (headers and body) from the upstream.
  • tries: a list of iterations made by the load balancer for this request.
    • balancer_start: A Unix timestamp for when the balancer started.
    • ip: The IP address of the contacted balancer.
    • port: The port number of the contacted balancer.
    • balancer_latency: The latency of the balancer expressed in milliseconds.
  • client_ip: The original client IP address.
  • workspace: The UUID of the workspace associated with this request.
  • workspace_name: The name of the workspace associated with this request.
  • upstream_uri: The URI, including query parameters, for the configured upstream.
  • authenticated_entity: Properties about the authenticated credential (if an authentication plugin has been enabled).
  • consumer: The authenticated consumer (if an authentication plugin has been enabled).
  • started_at: The unix timestamp of when the request has started to be processed.
  • source: Indicates whether the response is generated by kong or upstream.
  • upstream_status: The status code received from the upstream in the response.

Log plugins enabled on services and routes contain information about the service or route.

Kong process errors

This logging plugin logs HTTP request and response data, and also supports stream data (TCP, TLS, and UDP).

The Kong process error file is the Nginx error file. You can find it at the following path:

{prefix}/logs/error.log

Configure the prefix in kong.conf.

Custom fields by Lua

The custom_fields_by_lua configuration allows for the dynamic modification of log fields using Lua code. Below is a snippet of an example configuration that removes the route field from the logs:

curl -i -X POST http://localhost:8001/plugins \
... 
  --data config.custom_fields_by_lua.route="return nil"

Similarly, new fields can be added:

curl -i -X POST http://localhost:8001/plugins \
... 
  --data config.custom_fields_by_lua.header="return kong.request.get_header('h1')"

Plugin precedence and managing fields

All logging plugins use the same table for logging. If you set custom_fields_by_lua in one plugin, all logging plugins that execute after that plugin will also use the same configuration. For example, if you configure fields via custom_fields_by_lua in File Log, those same fields will appear in Kafka Log, since File Log executes first.

If you want all logging plugins to use the same configuration, we recommend using the Pre-function plugin to call kong.log.set_serialize_value so that the function is applied predictably and is easier to manage.

If you don’t want all logging plugins to use the same configuration, you need to manually disable the relevant fields in each plugin.

For example, if you configure a field in File Log that you don’t want appearing in Kafka Log, set that field to return nil in the Kafka Log plugin:

curl -i -X POST http://localhost:8001/plugins/ \
...
  --data config.name=kafka-log \
  --data config.custom_fields_by_lua.my_file_log_field="return nil"

See the plugin execution order reference for more details on plugin ordering.

Limitations

Lua code runs in a restricted sandbox environment, whose behavior is governed by the untrusted_lua configuration properties configuration properties.

Sandboxing consists of several limitations in the way the Lua code can be executed, for heightened security.

The following functions are not available because they can be used to abuse the system:

  • string.rep: Can be used to allocate millions of bytes in one operation.
  • {set|get}metatable: Can be used to modify the metatables of global objects (strings, numbers).
  • collectgarbage: Can be abused to kill the performance of other workers.
  • _G: Is the root node which has access to all functions. It is masked by a temporary table.
  • load{file|string}: Is deemed unsafe because it can grant access to the global environment.
  • raw{get|set|equal}: Potentially unsafe because sandboxing relies on some metatable manipulation.
  • string.dump: Can display confidential server information (such as implementation of functions).
  • math.randomseed: Can affect the host system. Kong Gateway already seeds the random number generator properly.
  • All os.* (except os.clock, os.difftime, and os.time). os.execute can significantly alter the host system.
  • io.*: Provides access to the hard drive.
  • dofile|require: Provides access to the hard drive.

The exclusion of require means that plugins must only use PDK functions kong.*. The ngx.* abstraction is also available, but it is not guaranteed to be present in future versions of the plugin.

In addition to the above restrictions:

  • All the provided modules (like string or table) are read-only and can’t be modified.

  • Bytecode execution is disabled.

  • The kong.cache points to a cache instance that is dedicated to the Serverless Functions plugins. It does not provide access to the global Kong Gateway cache. It only exposes the get method. Explicit write operations like set or invalidate are not available.

Further, as code runs in the context of the log phase, only PDK methods that can run in said phase can be used.