From 2a056078dd15422443714c3c57df2d06d71e8729 Mon Sep 17 00:00:00 2001
From: samugi <samuele@konghq.com>
Date: Sat, 15 Apr 2023 21:24:45 +0200
Subject: [PATCH] fix(tracing): balancer span precision

use nanoseconds to track balancer span's start and end times
---
 kong/init.lua                    | 4 ++++
 kong/tracing/instrumentation.lua | 6 +++---
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/kong/init.lua b/kong/init.lua
index 818423ebb85..b9e7c6b5c1c 100644
--- a/kong/init.lua
+++ b/kong/init.lua
@@ -89,6 +89,7 @@ local instrumentation = require "kong.tracing.instrumentation"
 local tablepool = require "tablepool"
 local table_new = require "table.new"
 local get_ctx_table = require("resty.core.ctx").get_ctx_table
+local time_ns = require "kong.tools.utils".time_ns
 
 
 local kong             = kong
@@ -1039,6 +1040,7 @@ end
 function Kong.balancer()
   -- This may be called multiple times, and no yielding here!
   local now_ms = now() * 1000
+  local now_ns = time_ns()
 
   local ctx = ngx.ctx
   if not ctx.KONG_BALANCER_START then
@@ -1079,6 +1081,7 @@ function Kong.balancer()
   tries[try_count] = current_try
 
   current_try.balancer_start = now_ms
+  current_try.balancer_start_ns = now_ns
 
   if try_count > 1 then
     -- only call balancer on retry, first one is done in `runloop.access.after`
@@ -1202,6 +1205,7 @@ function Kong.balancer()
   -- record try-latency
   local try_latency = ctx.KONG_BALANCER_ENDED_AT - current_try.balancer_start
   current_try.balancer_latency = try_latency
+  current_try.balancer_latency_ns = time_ns() - current_try.balancer_start_ns
 
   -- time spent in Kong before sending the request to upstream
   -- start_time() is kept in seconds with millisecond resolution.
diff --git a/kong/tracing/instrumentation.lua b/kong/tracing/instrumentation.lua
index 8f194a59352..3f10f496b6d 100644
--- a/kong/tracing/instrumentation.lua
+++ b/kong/tracing/instrumentation.lua
@@ -87,7 +87,7 @@ function _M.balancer(ctx)
     local span_name = "balancer try #" .. i
     local span_options = {
       span_kind = 3, -- client
-      start_time_ns = try.balancer_start * 1e6,
+      start_time_ns = try.balancer_start_ns,
       attributes = {
         ["net.peer.ip"] = try.ip,
         ["net.peer.port"] = try.port,
@@ -103,9 +103,9 @@ function _M.balancer(ctx)
         span:set_status(2)
       end
 
-      if try.balancer_latency ~= nil then
+      if try.balancer_latency_ns ~= nil then
         local try_upstream_connect_time = (tonumber(upstream_connect_time[i], 10) or 0) * 1000
-        span:finish((try.balancer_start + try.balancer_latency + try_upstream_connect_time) * 1e6)
+        span:finish(try.balancer_start_ns + try.balancer_latency_ns + try_upstream_connect_time * 1e6)
       else
         span:finish()
       end