feat(prometheus): expose controlplane connectivity state as a gauge

changelog/unreleased/kong/add-cp-connectivity-metric-prometheus.yml

@@ -0,0 +1,4 @@
+message: |
+  **Prometheus**: Added gauge to expose connectivity state to controlplane.
+type: feature
+scope: Plugin

kong/clustering/data_plane.lua

@@ -74,11 +74,20 @@ function _M.new(clustering)
 end
 
 
+local function set_control_plane_reachable(reachable)
+  local ok, err = ngx.shared.kong:safe_set("control_plane_reachable", reachable)
+  if not ok then
+    ngx_log(ngx_ERR, _log_prefix, "failed to set controlplane_reachable key in shm to " .. reachable .. " :", err)
+  end
+end
+
+
 function _M:init_worker(basic_info)
   -- ROLE = "data_plane"
 
   self.plugins_list = basic_info.plugins
   self.filters = basic_info.filters
+  set_control_plane_reachable(false)
 
   -- only run in process which worker_id() == 0
   assert(ngx.timer.at(0, function(premature)
@@ -98,13 +107,17 @@ local function send_ping(c, log_suffix)
 
   local _, err = c:send_ping(hash)
   if err then
+    set_control_plane_reachable(false)
     ngx_log(is_timeout(err) and ngx_NOTICE or ngx_WARN, _log_prefix,
             "unable to send ping frame to control plane: ", err, log_suffix)
 
   -- only log a ping if the hash changed
-  elseif hash ~= prev_hash then
-    prev_hash = hash
-    ngx_log(ngx_INFO, _log_prefix, "sent ping frame to control plane with hash: ", hash, log_suffix)
+  else
+    set_control_plane_reachable(true)
+    if hash ~= prev_hash then
+      prev_hash = hash
+      ngx_log(ngx_INFO, _log_prefix, "sent ping frame to control plane with hash: ", hash, log_suffix)
+    end
   end
 end
 
@@ -156,6 +169,7 @@ function _M:communicate(premature)
 
   local c, uri, err = clustering_utils.connect_cp(self, "/v1/outlet")
   if not c then
+    set_control_plane_reachable(false)
     ngx_log(ngx_WARN, _log_prefix, "connection to control plane ", uri, " broken: ", err,
                  " (retrying after ", reconnection_delay, " seconds)", log_suffix)
 
@@ -188,6 +202,7 @@ function _M:communicate(premature)
                                        filters = self.filters,
                                        labels = labels, }))
   if err then
+    set_control_plane_reachable(false)
     ngx_log(ngx_ERR, _log_prefix, "unable to send basic information to control plane: ", uri,
                      " err: ", err, " (retrying after ", reconnection_delay, " seconds)", log_suffix)
 
@@ -197,6 +212,7 @@ function _M:communicate(premature)
     end))
     return
   end
+  set_control_plane_reachable(true)
 
   local config_semaphore = semaphore.new(0)
 
@@ -302,16 +318,19 @@ function _M:communicate(premature)
       local data, typ, err = c:recv_frame()
       if err then
         if not is_timeout(err) then
+          set_control_plane_reachable(false)
           return nil, "error while receiving frame from control plane: " .. err
         end
 
         local waited = ngx_time() - last_seen
         if waited > PING_WAIT then
+          set_control_plane_reachable(false)
           return nil, "did not receive pong frame from control plane within " .. PING_WAIT .. " seconds"
         end
 
         goto continue
       end
+      set_control_plane_reachable(true)
 
       if typ == "close" then
         ngx_log(ngx_DEBUG, _log_prefix, "received close frame from control plane", log_suffix)

kong/plugins/prometheus/exporter.lua

@@ -10,6 +10,7 @@ local lower = string.lower
 local ngx_timer_pending_count = ngx.timer.pending_count
 local ngx_timer_running_count = ngx.timer.running_count
 local get_all_upstreams = balancer.get_all_upstreams
+
 if not balancer.get_all_upstreams then -- API changed since after Kong 2.5
   get_all_upstreams = require("kong.runloop.balancer.upstreams").get_all_upstreams
 end
@@ -65,6 +66,14 @@ local function init()
                                           "0 is unreachable",
                                           nil,
                                           prometheus.LOCAL_STORAGE)
+  if role == "data_plane" then
+    metrics.cp_reachable = prometheus:gauge("control_plane_reachable",
+                                          "Control plane reachable from gateway, " ..
+                                          "0 is unreachable",
+                                          nil,
+                                          prometheus.LOCAL_STORAGE)
+  end
+
   metrics.node_info = prometheus:gauge("node_info",
                                        "Kong Node metadata information",
                                        {"node_id", "version"},
@@ -449,6 +458,15 @@ local function metric_data(write_fn)
       kong.log.err("prometheus: failed to reach database while processing",
                   "/metrics endpoint: ", err)
     end
+
+    if role == "data_plane" then
+      local cp_reachable = ngx.shared.kong:get("control_plane_reachable")
+      if cp_reachable then
+        metrics.cp_reachable:set(1)
+      else
+        metrics.cp_reachable:set(0)
+      end
+    end
   end
 
   local phase = get_phase()

spec/03-plugins/26-prometheus/04-status_api_spec.lua

@@ -529,3 +529,70 @@ describe("Plugin: prometheus (access) granular metrics switch", function()
 
 end)
 end
+
+describe("CP/DP connectivity state #", function ()
+  local status_client
+
+  local function get_metrics()
+    if not status_client then
+      status_client = helpers.http_client("127.0.0.1", tcp_status_port, 20000)
+      status_client.reopen = true -- retry on a closed connection
+    end
+
+    local res, err = status_client:get("/metrics")
+
+    assert.is_nil(err, "failed GET /metrics: " .. tostring(err))
+    return assert.res_status(200, res)
+  end
+
+  setup(function()
+    local bp = helpers.get_db_utils()
+
+    bp.plugins:insert {
+      protocols = { "http", "https", "grpc", "grpcs", "tcp", "tls" },
+      name = "prometheus",
+    }
+
+    assert(helpers.start_kong({
+      role = "control_plane",
+      prefix = "prom_cp",
+      cluster_cert = "spec/fixtures/kong_clustering.crt",
+      cluster_cert_key = "spec/fixtures/kong_clustering.key",
+      cluster_listen = "127.0.0.1:9005",
+      plugins = "bundled, prometheus",
+    }))
+
+    assert(helpers.start_kong({
+      role = "data_plane",
+      database = "off",
+      prefix = "prom_dp",
+      cluster_cert = "spec/fixtures/kong_clustering.crt",
+      cluster_cert_key = "spec/fixtures/kong_clustering.key",
+      cluster_control_plane = "127.0.0.1:9005",
+      proxy_listen = "0.0.0.0:9000",
+      worker_state_update_frequency = 1,
+      status_listen = "0.0.0.0:" .. tcp_status_port,
+      nginx_worker_processes = 1,
+      dedicated_config_processing = "on",
+      plugins = "bundled, prometheus",
+    }))
+    status_client = helpers.http_client("127.0.0.1", tcp_status_port, 20000)
+  end)
+
+  teardown(function()
+    if status_client then
+      status_client:close()
+    end
+
+    helpers.stop_kong("prom_dp")
+  end)
+
+  it("exposes controlplane connectivity status", function ()
+    local body = get_metrics()
+    assert.matches('kong_control_plane_reachable 1', body, nil, true)
+
+    helpers.stop_kong("prom_cp")
+    local body  = get_metrics()
+    assert.matches('kong_control_plane_reachable 0', body, nil, true)
+  end)
+end)