fix(runloop): use upstream status code in passive health check

CHANGELOG.md

@@ -86,13 +86,15 @@
   [#10352](https://github.com/Kong/kong/pull/10352)
 - Fix an issue where validation to regex routes may be skipped when the old-fashioned config is used for DB-less Kong.
   [#10348](https://github.com/Kong/kong/pull/10348)
+- Fix an issue where balancer passive healthcheck would use wrong status code when kong changes status code
+  from upstream in `header_filter` phase.
+  [#10325](https://github.com/Kong/kong/pull/10325)
 
 ### Dependencies
 
 - Bumped lua-resty-session from 4.0.2 to 4.0.3
   [#10338](https://github.com/Kong/kong/pull/10338)
 
-
 ## 3.2.0
 
 ### Breaking Changes

kong/runloop/handler.lua

@@ -11,7 +11,7 @@ local certificate  = require "kong.runloop.certificate"
 local concurrency  = require "kong.concurrency"
 local lrucache     = require "resty.lrucache"
 local marshall     = require "kong.cache.marshall"
-local ktls         = require("resty.kong.tls")
+local ktls         = require "resty.kong.tls"
 
 local PluginsIterator = require "kong.runloop.plugins_iterator"
 local instrumentation = require "kong.tracing.instrumentation"
@@ -1511,7 +1511,10 @@ return {
       -- Report HTTP status for health checks
       local balancer_data = ctx.balancer_data
       if balancer_data and balancer_data.balancer_handle then
-        local status = ngx.status
+        -- https://nginx.org/en/docs/http/ngx_http_upstream_module.html#variables
+        -- because of the way of Nginx do the upstream_status variable, it may be
+        -- a string or a number, so we need to parse it to get the status
+        local status = tonumber(sub(var.upstream_status or "", -3)) or ngx.status
         if status == 504 then
           balancer_data.balancer.report_timeout(balancer_data.balancer_handle)
         else

spec/02-integration/05-proxy/10-balancer/01-healthchecks_spec.lua

@@ -1183,6 +1183,72 @@ for _, strategy in helpers.each_strategy() do
               end
             end)
 
+            it("perform passive health checks in downstream status code was changed", function()
+
+              for nfails = 1, 3 do
+
+                bu.begin_testcase_setup(strategy, bp)
+                -- configure healthchecks
+                local upstream_name, upstream_id = bu.add_upstream(bp, {
+                  healthchecks = bu.healthchecks_config {
+                    passive = {
+                      unhealthy = {
+                        http_failures = nfails,
+                      }
+                    }
+                  }
+                })
+                local port1 = bu.add_target(bp, upstream_id, localhost)
+                local port2 = bu.add_target(bp, upstream_id, localhost)
+                local api_host, service_id = bu.add_api(bp, upstream_name)
+                bp.plugins:insert({
+                  name = "pre-function",
+                  service = { id = service_id },
+                  config = {
+                    header_filter ={ 
+                      [[
+                        ngx.exit(200)
+                    ]],
+                    },
+                  }
+                })
+
+                bu.end_testcase_setup(strategy, bp)
+
+                local requests = bu.SLOTS * 2 -- go round the balancer twice
+
+                -- setup target servers:
+                -- server2 will only respond for part of the test,
+                -- then server1 will take over.
+                local server2_oks = math.floor(requests / 4)
+                local server1 = https_server.new(port1, localhost)
+                local server2 = https_server.new(port2, localhost)
+                server1:start()
+                server2:start()
+
+                -- Go hit them with our test requests
+                local client_oks1, client_fails1 = bu.client_requests(bu.SLOTS, api_host)
+                assert(bu.direct_request(localhost, port2, "/unhealthy"))
+                local client_oks2, client_fails2 = bu.client_requests(bu.SLOTS, api_host)
+
+                local client_oks = client_oks1 + client_oks2
+                local client_fails = client_fails1 + client_fails2
+
+                -- collect server results; hitcount
+                local count1 = server1:shutdown()
+                local count2 = server2:shutdown()
+
+                -- verify
+                assert.are.equal(requests - server2_oks - nfails, count1.ok)
+                assert.are.equal(server2_oks, count2.ok)
+                assert.are.equal(0, count1.fail)
+                assert.are.equal(nfails, count2.fail)
+
+                assert.are.equal(client_oks, requests)
+                assert.are.equal(0, client_fails)
+              end
+            end)
+
             it("threshold for health checks", function()
               local fixtures = {
                 dns_mock = helpers.dns_mock.new()