Kong Zipkin Plugin

This is a plugin for the Kong API gateway to integrate with the Zipkin distributed tracing system. It allows for some degree of Zipkin instrumentation of connections between systems where one or both ends can't be directly instrumented.

This code has not been used in a production deployment by the author - you should verify it works for you before deploying.

Scenarios

Simulate Server

--------    ------    --------
|client| -> |Kong| -> |server|
--------    ------    --------
   |           |
   V           V
--------    --------
|Zipkin|    |Zipkin|
--------    --------

Server cannot be instrumented, so Kong impersonates the server to Zipkin, continuing the trace propagated from the client in B3 headers

Simulate Client

--------    ------    --------
|client| -> |Kong| -> |server|
--------    ------    --------
              |           |
              V           V
            --------    --------
            |Zipkin|    |Zipkin|
            --------    --------

Client cannot be instrumented, so Kong impersonates the client to Zipkin, initiating a new trace and propagating the B3 headers to the server

Simulate Client and server

--------    ------    --------
|client| -> |Kong| -> |server|
--------    ------    --------
              |           
              V           
            --------
            |Zipkin|
            --------

Neither client nor server can be instrumented, so Kong impersonates both ends of the communication to Zipkin

Usage

Requires Kong and Zipkin instances to exist
Install the plugin on Kong:

Obtain plugin:

$ git clone git@github.com:sfhardman/kong-plugin-zipkin.git /opt/plugins/kong-plugin-zipkin

Edit kong.conf:
```
 lua_package_path = /opt/plugins/kong-plugin-zipkin/?.lua;;

 custom_plugins = zipkin
```
Restart Kong

Add the plugin to an API:

 $ curl -i -X POST \
   --url http://localhost:8001/apis/ \
   --data 'name=example-api' \
   --data 'hosts=example.com' \
   --data 'upstream_url=http://httpbin.org'

 $ curl -i -X POST \
   --url http://localhost:8001/apis/example-api/plugins/ \
   --data 'name=zipkin' \
   --data 'config.zipkin_url=http://10.0.0.99:9411' \
   --data 'config.sample_once_every_n_requests=1' \
   --data 'config.simulate_server=false'

 # a Kong restart appears to be needed here to cause the plugin to register

 $ curl -i -X GET \
   --url http://localhost:8000/headers \
   --header 'Host: example.com'

 HTTP/1.1 200 OK
 ...

  {
    "headers": {
      "Accept": "*/*",
      "Connection": "close",
      "Host": "httpbin.org",
      "User-Agent": "curl/7.47.0",
      "X-B3-Sampled": "true",
      "X-B3-Spanid": "cf7fffa067b446fe",
      "X-B3-Traceid": "c14cad40e0e24232b94a2a25db2a0ca9"
    }
  }

Parameters

zipkin_url: Base URL of the Zipkin instance (protocol://host:port)
sample_once_every_n_requests: Causes the plugin to sample the request at this frequency. Set to zero to never sample. Set to one to always sample. Regardless of this setting the plugin will always sample if it receives B3 headers indicating the caller is sampling (X-B3-Sampled == 1 or X-B3-Flags == 1)
simulate_server: Tells the plugin to impersonate the server which will process the request (Kong upstream_url). Note that Kong will impersonate the client automatically if it is sampling and there are no B3 headers from the client

Limitations

Uses Zipkin REST API, not gRPC
Kong random number generator seeding does not work correctly when running with KONG_LUA_CODE_CACHE=false, and this results in all generated trace / span ID's being the same. To workaround for development uncomment the randomseed line in handler.lua (function plugin:access)
Only millisecond precision timing, not microsecond as preferred by Zipkin

sfhardman / kong-plugin-zipkin