in_monitor_agent: change default visibility of config, retry, and debug info

**Which issue(s) this PR fixes**:
Fixes #

**What this PR does / why we need it**:
This PR updates the default behavior of the `monitor_agent` API to provide a more minimal and predictable response footprint.

### Before
The HTTP API (`/api/plugins.json`, etc.) included `config`, `retry` state, and `instance_variables` of plugins by default (or when dynamically queried with parameters like `debug=1`, `with_config`, `with_retry`, or `with_ivars`).

This resulted in unnecessarily verbose payloads that exposed deep internal plugin states not typically required for standard health monitoring.

### After
Inclusion of these detailed internal states is now disabled by default to reduce payload size and enforce explicit configuration.

* Changed
  * `include_config` default is changed from `true` to `false`.
  * `include_retry` default is changed from `true` to `false`.
  * The API no longer allows URL query parameters to override these settings.
* Added
  * `include_debug_info` parameter to explicitly control the visibility of internal instance variables (default `false`).
  * Debug information (via queries such as `debug=1` or `with_ivars=xxx`) is now only included when this parameter is explicitly enabled in the configuration block.

**Docs Changes**:

**Release Note**:
* in_monitor_agent: change default visibility of config, retry, and debug info

Signed-off-by: Shizuo Fujita <fujita@clear-code.com>

Author: Watson1978

lib/fluent/plugin/in_monitor_agent.rb

@@ -37,9 +37,11 @@ class MonitorAgentInput < Input
     desc 'Determine the rate to emit internal metrics as events.'
     config_param :emit_interval, :time, default: 60
     desc 'Determine whether to include the config information.'
-    config_param :include_config, :bool, default: true
+    config_param :include_config, :bool, default: false
     desc 'Determine whether to include the retry information.'
-    config_param :include_retry, :bool, default: true
+    config_param :include_retry, :bool, default: false
+    desc 'Determine whether to include the debug information.'
+    config_param :include_debug_info, :bool, default: false
 
     class APIHandler
       def initialize(agent)
@@ -151,28 +153,23 @@ def build_option(req)
         # parse ?=query string
         qs.merge!(req.query || {})
 
-        # if ?debug=1 is set, set :with_debug_info for get_monitor_info
-        # and :pretty_json for render_json_error
-        opts = { query: qs }
-        if qs['debug'.freeze].first
-          opts[:with_debug_info] = true
-          opts[:pretty_json] = true
-        end
-
-        if ivars = qs['with_ivars'.freeze].first
-          opts[:ivars] = ivars.split(',')
-        end
+        opts = {
+          query: qs,
+          with_config: @agent.include_config,
+          with_retry: @agent.include_retry
+        }
 
-        if with_config = qs['with_config'.freeze].first
-          opts[:with_config] = Fluent::Config.bool_value(with_config)
-        else
-          opts[:with_config] = @agent.include_config
-        end
+        if @agent.include_debug_info
+          # if ?debug=1 is set, set :with_debug_info for get_monitor_info
+          # and :pretty_json for render_json_error
+          if qs['debug'.freeze].first
+            opts[:with_debug_info] = true
+            opts[:pretty_json] = true
+          end
 
-        if with_retry = qs['with_retry'.freeze].first
-          opts[:with_retry] = Fluent::Config.bool_value(with_retry)
-        else
-          opts[:with_retry] = @agent.include_retry
+          if ivars = qs['with_ivars'.freeze].first
+            opts[:ivars] = ivars.split(',')
+          end
         end
 
         opts

test/plugin/test_in_monitor_agent.rb

@@ -35,7 +35,9 @@ def test_configure
     assert_equal(24220, d.instance.port)
     assert_equal(nil, d.instance.tag)
     assert_equal(60, d.instance.emit_interval)
-    assert_true d.instance.include_config
+    assert_false d.instance.include_config
+    assert_false d.instance.include_retry
+    assert_false d.instance.include_debug_info
   end
 
   sub_test_case "collect in_monitor_agent plugin statistics" do
@@ -614,15 +616,17 @@ def get(uri, header = {})
       d.instance_shutdown
     end
 
-    data(:with_config_and_retry_yes => [true, true, "?with_config=yes&with_retry"],
-         :with_config_and_retry_no => [false, false, "?with_config=no&with_retry=no"])
+    data(:with_config_and_retry_yes => [true, true, "?with_config=no&with_retry=no"],
+         :with_config_and_retry_no => [false, false, "?with_config=yes&with_retry=yes"])
     test "/api/plugins.json with query parameter. query parameter is preferred than include_config" do |(with_config, with_retry, query_param)|
 
       d = create_driver("
   @type monitor_agent
   bind '127.0.0.1'
   port #{@port}
   tag monitor
+  include_config #{with_config}
+  include_retry #{with_retry}
 ")
       d.instance.start
       expected_test_in_response = {
@@ -659,6 +663,7 @@ def get(uri, header = {})
       }
       expected_null_response["config"] = {"@id" => "null", "@type" => "null"} if with_config
       expected_null_response["retry"] = {} if with_retry
+      # The values are retrieved based on the configuration settings, regardless of query parameters.
       response = JSON.parse(get("http://127.0.0.1:#{@port}/api/plugins.json#{query_param}").body)
       test_in_response = response["plugins"][0]
       null_response = response["plugins"][5]
@@ -674,6 +679,7 @@ def get(uri, header = {})
   bind '127.0.0.1'
   port #{@port}
   tag monitor
+  include_debug_info true
 ")
       d.instance.start
       expected_test_in_response = {
@@ -710,7 +716,7 @@ def get(uri, header = {})
         "flush_time_count" => Integer,
         "drop_oldest_chunk_count" => Integer,
       }
-      response = JSON.parse(get("http://127.0.0.1:#{@port}/api/plugins.json?with_config=no&with_retry=no&with_ivars=id,num_errors").body)
+      response = JSON.parse(get("http://127.0.0.1:#{@port}/api/plugins.json?with_config=no&with_retry=no&with_ivars=id,non_existed_ivar").body)
       test_in_response = response["plugins"][0]
       null_response = response["plugins"][5]
       assert_equal(expected_test_in_response, test_in_response)
@@ -758,6 +764,7 @@ def get(uri, header = {})
   bind '127.0.0.1'
   port #{@port}
   tag monitor
+  include_debug_info true
 ")
       d.instance.start
       # To check pretty print
@@ -823,7 +830,8 @@ def write(chunk)
   @type monitor_agent
   bind '127.0.0.1'
   port #{@port}
-  include_config no
+  include_config false
+  include_retry true
 ")
       d.instance.start
       output = @ra.outputs[0]
@@ -968,4 +976,86 @@ def filter(tag, time, record)
       d.instance_shutdown
     end
   end
+
+  sub_test_case 'debug information exposure configurations' do
+    setup do
+      @port = unused_port(protocol: :tcp)
+
+      conf = <<~EOC
+        <source>
+          @type test_in
+          @id test_in
+        </source>
+      EOC
+      @ra = Fluent::RootAgent.new(log: $log)
+      stub(Fluent::Engine).root_agent { @ra }
+      @ra = configure_ra(@ra, conf)
+    end
+
+    def config(include_debug_info:)
+      <<~"CONFIG"
+        @type monitor_agent
+        bind '127.0.0.1'
+        port #{@port}
+        tag monitor
+        include_debug_info #{include_debug_info}
+      CONFIG
+    end
+
+    sub_test_case "include_debug_info true" do
+      test "'/api/plugins.json?with_ivars=xxx' expose instance variables" do
+        d = create_driver(config(include_debug_info: true))
+        d.instance.start
+
+        response = JSON.parse(get("http://127.0.0.1:#{@port}/api/plugins.json?with_ivars=id").body)
+        test_in_response = response["plugins"][0]
+        assert_equal({"id" => "test_in"} , test_in_response["instance_variables"])
+
+        d.instance_shutdown
+      end
+
+      test "'/api/plugins.json?debug=1' expose instance variables" do
+        d = create_driver(config(include_debug_info: true))
+        d.instance.start
+
+        response = JSON.parse(get("http://127.0.0.1:#{@port}/api/plugins.json?debug=1").body)
+        test_in_response = response["plugins"][0]
+        assert_true(test_in_response.has_key?("instance_variables"))
+        # check existence about one of typical debug element
+        assert_false(test_in_response["instance_variables"]["log"].nil?)
+
+        d.instance_shutdown
+      end
+    end
+
+    sub_test_case "include_debug_info false" do
+      test "'/api/plugins.json?with_ivars=xxx' does not expose instance variables" do
+        d = create_driver(config(include_debug_info: false))
+        d.instance.start
+
+        response = JSON.parse(get("http://127.0.0.1:#{@port}/api/plugins.json?with_ivars=id").body)
+        test_in_response = response["plugins"][0]
+        assert_false(test_in_response.has_key?("instance_variables"))
+
+        no_query_response = JSON.parse(get("http://127.0.0.1:#{@port}/api/plugins.json").body)
+        assert_equal(response, no_query_response)
+
+        d.instance_shutdown
+      end
+
+      test "'/api/plugins.json?debug=1' does not expose instance variables" do
+        d = create_driver(config(include_debug_info: false))
+        d.instance.start
+
+        response = JSON.parse(get("http://127.0.0.1:#{@port}/api/plugins.json?debug=1").body)
+        test_in_response = response["plugins"][0]
+        assert_false(test_in_response.has_key?("instance_variables"))
+
+        no_query_response = JSON.parse(get("http://127.0.0.1:#{@port}/api/plugins.json").body)
+        assert_equal(response, no_query_response)
+
+        d.instance_shutdown
+      end
+    end
+  end
 end