fix(cmd) do not reload the declarative config on kong reload if no de…

…clarative config given

### Summary

On `kong reload` we do not want to reload the declarative configuration that was given on e.g.
`kong start` (because that could overwrite the more recent configuration send to `:8000/config`).
Thus we want to clear the declarative config from the `.kong_env` before we reload a new
configuration.

kong/cmd/reload.lua

@@ -29,6 +29,10 @@ local function execute(args)
     prefix = args.prefix
   }))
 
+  if not new_config.declarative_config then
+    conf.declarative_config = nil
+  end
+
   assert(prefix_handler.prepare_prefix(conf, args.nginx_conf))
   assert(nginx_signals.reload(conf))
 

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

@@ -316,7 +316,9 @@ describe("kong reload #" .. strategy, function()
             - example.test
       ]], yaml_file)
 
-      assert(kong_reload(strategy, "reload --prefix " .. helpers.test_conf.prefix))
+      assert(kong_reload(strategy, "reload --prefix " .. helpers.test_conf.prefix, {
+        declarative_config = yaml_file,
+      }))
 
       helpers.wait_until(function()
         pok, admin_client = pcall(helpers.admin_client)
@@ -384,7 +386,102 @@ describe("kong reload #" .. strategy, function()
         return true
       end)
 
+      assert(kong_reload(strategy, "reload --prefix " .. helpers.test_conf.prefix))
+
       admin_client = assert(helpers.admin_client())
+      local res = assert(admin_client:send {
+        method = "GET",
+        path = "/services",
+      })
+      assert.res_status(200, res)
+
+      local body = assert.res_status(200, res)
+      local json = cjson.decode(body)
+      assert.same(1, #json.data)
+      assert.same(ngx.null, json.next)
+      admin_client:close()
+
+      return "my-service" == json.data[1].name
+    end)
+
+    it("preserves declarative config from memory even when kong was started with a declarative_config", function()
+      local yaml_file = helpers.make_yaml_file [[
+        _format_version: "1.1"
+        services:
+        - name: my-service-on-start
+          url: http://127.0.0.1:15555
+          routes:
+          - name: example-route
+            hosts:
+            - example.test
+      ]]
+
+      local pok, admin_client
+
+      finally(function()
+        helpers.stop_kong(helpers.test_conf.prefix, true)
+        if admin_client then
+          admin_client:close()
+        end
+      end)
+
+      assert(helpers.start_kong({
+        database = "off",
+        nginx_worker_processes = 1,
+        declarative_config = yaml_file,
+        nginx_conf = "spec/fixtures/custom_nginx.template",
+      }))
+
+      helpers.wait_until(function()
+        pok, admin_client = pcall(helpers.admin_client)
+        if not pok then
+          return false
+        end
+
+        local res = assert(admin_client:send {
+          method = "GET",
+          path = "/services",
+        })
+        assert.res_status(200, res)
+
+        local body = assert.res_status(200, res)
+        local json = cjson.decode(body)
+        assert.same(1, #json.data)
+        assert.same(ngx.null, json.next)
+
+        admin_client:close()
+
+        return "my-service-on-start" == json.data[1].name
+      end, 10)
+
+      helpers.wait_until(function()
+        pok, admin_client = pcall(helpers.admin_client)
+        if not pok then
+          return false
+        end
+
+        local res = assert(admin_client:send {
+          method = "POST",
+          path = "/config",
+          headers = {
+            ["Content-Type"] = "application/json",
+          },
+          body = {
+            _format_version = "1.1",
+            services = {
+              {
+                name = "my-service",
+                url = "http://127.0.0.1:15555",
+              }
+            }
+          },
+        }, 10)
+        assert.res_status(201, res)
+
+        admin_client:close()
+
+        return true
+      end)
 
       assert(kong_reload(strategy, "reload --prefix " .. helpers.test_conf.prefix))
 
@@ -477,7 +574,9 @@ describe("kong reload #" .. strategy, function()
             weight: 100
       ]], yaml_file)
 
-      assert(kong_reload(strategy, "reload --prefix " .. helpers.test_conf.prefix))
+      assert(kong_reload(strategy, "reload --prefix " .. helpers.test_conf.prefix, {
+        declarative_config = yaml_file,
+      }))
 
       helpers.wait_until(function()
         pok, admin_client = pcall(helpers.admin_client)
@@ -608,8 +707,9 @@ describe("key-auth plugin invalidation on dbless reload #off", function()
         keyauth_credentials:
         - key: my-new-key
     ]], yaml_file)
-    assert(kong_reload("off", "reload --prefix " .. helpers.test_conf.prefix))
-
+    assert(kong_reload("off", "reload --prefix " .. helpers.test_conf.prefix, {
+      declarative_config = yaml_file,
+    }))
 
     local res