fix(cmd) check db connection on reload

### Summary

Database connection may be changed on `kong reload`, so it is good that we
check that before we signal to actual Kong server process to `reload`.

kong/cmd/reload.lua

@@ -1,9 +1,12 @@
 local prefix_handler = require "kong.cmd.utils.prefix_handler"
 local nginx_signals = require "kong.cmd.utils.nginx_signals"
 local conf_loader = require "kong.conf_loader"
+local kong_global = require "kong.global"
 local pl_path = require "pl.path"
 local pl_file = require "pl.file"
 local log = require "kong.cmd.utils.log"
+local DB = require "kong.db"
+
 
 local function execute(args)
   log.disable()
@@ -34,11 +37,19 @@ local function execute(args)
   end
 
   assert(prefix_handler.prepare_prefix(conf, args.nginx_conf, nil, true))
+
+  _G.kong = kong_global.new()
+  kong_global.init_pdk(_G.kong, conf)
+
+  local db = assert(DB.new(conf))
+  assert(db:init_connector())
+
   assert(nginx_signals.reload(conf))
 
   log("Kong reloaded")
 end
 
+
 local lapp = [[
 Usage: kong reload [OPTIONS]
 
@@ -56,6 +67,7 @@ Options:
  --nginx-conf     (optional string) custom Nginx configuration template
 ]]
 
+
 return {
   lapp = lapp,
   execute = execute

spec/02-integration/02-cmd/03-reload_spec.lua

@@ -622,6 +622,22 @@ describe("kong reload #" .. strategy, function()
       assert.False(ok)
       assert.matches("Error: nginx not running in prefix: " .. helpers.test_conf.prefix, err, nil, true)
     end)
+
+    if strategy ~= "off" then
+      it("complains when database connection is invalid", function()
+        assert(helpers.start_kong({
+          proxy_listen = "0.0.0.0:9002"
+        }, nil, true))
+
+        local ok = helpers.kong_exec("reload --conf " .. helpers.test_conf_path, {
+          database = strategy,
+          pg_port = 1234,
+          cassandra_port = 1234,
+        })
+
+        assert.False(ok)
+      end)
+    end
   end)
 end)