Correlate requests and responses using a unique ID transmitted over an HTTP header.


Terminology

  • plugin: a plugin executing actions inside Kong before or after a request has been proxied to the upstream API.
  • API: (deprecated) the Kong entity representing your upstream service placed behind Kong, for which Kong proxies requests to.
  • Service: the Kong entity representing an external upstream API or microservice.
  • Route: the Kong entity representing a way to map downstream requests to upstream services.
  • Consumer: the Kong entity representing a developer or machine using the API. When using Kong, a Consumer only communicates with Kong which proxies every call to the said upstream API.
  • Credential: a unique string associated with a Consumer, also referred to as an API key.
  • upstream service: this refers to your own API/service sitting behind Kong, to which client requests are forwarded.

Configuration

Enabling the plugin for a Service

Configure on top of a Service by executing the following request on your Kong server:

$ curl -X POST http://kong:8001/services/{service}/plugins \
    --data "name=correlation-id"  \
    --data "config.header_name=Kong-Request-ID" \
    --data "config.generator=uuid#counter" \
    --data "config.echo_downstream=false"
  • service: the id or name of the Service that this plugin configuration will target.

Enabling the plugin for a Route

Configure on top of a Route with:

$ curl -X POST http://kong:8001/routes/{route_id}/plugins \
    --data "name=correlation-id"  \
    --data "config.header_name=Kong-Request-ID" \
    --data "config.generator=uuid#counter" \
    --data "config.echo_downstream=false"
  • route_id: the id of the Route that this plugin configuration will target.

Enabling the plugin for an API

If you are using the deprecated API entity, you can configure on top of an API by executing the following request on your Kong server:

$ curl -X POST http://kong:8001/apis/{api}/plugins \
    --data "name=correlation-id"  \
    --data "config.header_name=Kong-Request-ID" \
    --data "config.generator=uuid#counter" \
    --data "config.echo_downstream=false"
  • api: either id or name of the API that this plugin configuration will target.

Enabling the plugin for a Consumer

You can use the http://localhost:8001/plugins endpoint to target Consumers:

$ curl -X POST http://kong:8001/plugins \
    --data "name=correlation-id" \
    --data "consumer_id={consumer_id}"  \
    --data "config.header_name=Kong-Request-ID" \
    --data "config.generator=uuid#counter" \
    --data "config.echo_downstream=false"

Where consumer_id: The id of the Consumer we want to associate with this plugin.

You can combine adding consumer_id and service_id in the same request.

Once applied, any user with a valid credential can access the Service/API. To restrict usage to only some of the authenticated users, also add the ACL plugin (not covered here) and create whitelist or blacklist groups of users.

Global plugins

All plugins can be configured using the http:/kong:8001/plugins/ endpoint. A plugin which is not associated to any API, Service, Route or Consumer is considered "global", and will be run on every request. Read the Plugin Reference and the Plugin Precedence sections for more information.

Parameters

Here's a list of all the parameters which can be used in this plugin's configuration:

form parameterdefaultdescription
nameThe name of the plugin to use, in this case correlation-id
api_idThe id of the API which this plugin will target.
service_idThe id of the Service which this plugin will target.
route_idThe id of the Route which this plugin will target.
consumer_idThe id of the Consumer which this plugin will target.
config.header_name
optional

Kong-Request-ID

The HTTP header name to use for the correlation ID.

config.generator
optional

uuid#counter

The generator to use for the correlation ID. Accepted values are uuid, uuid#counter and tracker See Generators.

config.echo_downstream
optional

false

Whether to echo the header back to downstream (the client).

How it works

When enabled, this plugin will add a new header to all of the requests processed by Kong. This header bears the name configured in config.header_name, and a unique value generated according to config.generator.

This header is always added to calls to your upstream services, and optionally echoed back to your clients according to the config.echo_downstream setting.

If a header bearing the same name is already present in the client request, it is honored and this plugin will not temper with it.

Generators

uuid

Format: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

Using this format, a UUID is generated in its hexadecimal form for each request.

uuid#counter

Format: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx#counter

In this format, a single UUID is generated on a per-worker basis, and further requests simply append a counter to the UUID after a # character. The counter value starts at 0 for each worker, and gets incremented independantly of the others.

This format provides a better performance, but might be harder to store or process for analizing (due to its format and low cardinality).

tracker

Format: ip-port-pid-connection-connection_requests-timestamp

In this format, the correlation id contains more practical implications for each request.

The following is a detailed description of the field

form parameter description
ip an address of the server which accepted a request
port port of the server which accepted a request
pid pid of the nginx worker process
connection connection serial number
connection_requests current number of requests made through a connection
timestamp a floating-point number for the elapsed time in seconds (including milliseconds as the decimal part) from the epoch for the current time stamp from the nginx cached time

FAQ

Can I see my correlation ids in my Kong logs?

The correlation id will not show up in the Nginx access or error logs. As such, we suggest you use this plugin alongside one of the Logging plugins, or store this id on your backend-side.

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