feat: Add additional modes for config endpoint (cortexproject#3645)

This adds a `mode` query parameter for the config endpoint:

- `/config?mode=diff`: Shows the YAML configuration with all values that
differ from the defaults.

- `/config?mode=defaults`: Shows the YAML configuration with all the
default values.

Signed-off-by: Christian Simon <[email protected]>

Co-authored-by: Marco Pracucci <[email protected]>

CHANGELOG.md

@@ -26,6 +26,9 @@
 * [ENHANCEMENT] Compactor: tenants marked for deletion will now be fully cleaned up after some delay since deletion of last block. Cleanup includes removal of remaining marker files (including tenant deletion mark file) and files under `debug/metas`. #3613
 * [ENHANCEMENT] Compactor: retry compaction of a single tenant on failure instead of re-running compaction for all tenants. #3627
 * [ENHANCEMENT] Querier: Implement result caching for tenant query federation. #3640
+* [ENHANCEMENT] API: Add a `mode` query parameter for the config endpoint: #3645
+  * `/config?mode=diff`: Shows the YAML configuration with all values that differ from the defaults.
+  * `/config?mode=defaults`: Shows the YAML configuration with all the default values.
 * [ENHANCEMENT] OpenStack Swift: added the following config options to OpenStack Swift backend client: #3660
   - Chunks storage: `-swift.auth-version`, `-swift.max-retries`, `-swift.connect-timeout`, `-swift.request-timeout`.
   - Blocks storage: ` -blocks-storage.swift.auth-version`, ` -blocks-storage.swift.max-retries`, ` -blocks-storage.swift.connect-timeout`, ` -blocks-storage.swift.request-timeout`.

docs/api/_index.md

@@ -109,6 +109,20 @@ GET /config
 
 Displays the configuration currently applied to Cortex (in YAML format), including default values and settings via CLI flags. Sensitive data is masked. Please be aware that the exported configuration **doesn't include the per-tenant overrides**.
 
+#### Different modes
+
+```
+GET /config?mode=diff
+```
+
+Displays the configuration currently applied to Cortex (in YAML format) as before, but containing only the values that differ from the  default values.
+
+```
+GET /config?mode=defaults
+```
+
+Displays the configuration using only the default values.
+
 ### Services status
 
 ```

pkg/api/api.go

@@ -166,10 +166,11 @@ func (a *API) RegisterAlertmanager(am *alertmanager.MultitenantAlertmanager, tar
 }
 
 // RegisterAPI registers the standard endpoints associated with a running Cortex.
-func (a *API) RegisterAPI(httpPathPrefix string, cfg interface{}) {
-	a.indexPage.AddLink(SectionAdminEndpoints, "/config", "Current Config")
+func (a *API) RegisterAPI(httpPathPrefix string, actualCfg interface{}, defaultCfg interface{}) {
+	a.indexPage.AddLink(SectionAdminEndpoints, "/config", "Current Config (including the default values)")
+	a.indexPage.AddLink(SectionAdminEndpoints, "/config?mode=diff", "Current Config (show only values that differ from the defaults)")
 
-	a.RegisterRoute("/config", configHandler(cfg), false, "GET")
+	a.RegisterRoute("/config", configHandler(actualCfg, defaultCfg), false, "GET")
 	a.RegisterRoute("/", indexHandler(httpPathPrefix, a.indexPage), false, "GET")
 	a.RegisterRoute("/debug/fgprof", fgprof.Handler(), false, "GET")
 }

pkg/api/handlers.go

@@ -2,14 +2,15 @@ package api
 
 import (
 	"context"
+	"fmt"
 	"html/template"
 	"net/http"
 	"path"
+	"reflect"
 	"regexp"
 	"sync"
 
 	"github.com/go-kit/kit/log"
-	"github.com/go-kit/kit/log/level"
 	"github.com/gorilla/mux"
 	"github.com/opentracing-contrib/go-stdlib/nethttp"
 	"github.com/opentracing/opentracing-go"
@@ -115,20 +116,109 @@ func indexHandler(httpPathPrefix string, content *IndexPageContent) http.Handler
 	}
 }
 
-func configHandler(cfg interface{}) http.HandlerFunc {
-	return func(w http.ResponseWriter, r *http.Request) {
-		out, err := yaml.Marshal(cfg)
-		if err != nil {
-			http.Error(w, err.Error(), http.StatusInternalServerError)
-			return
+func yamlMarshalUnmarshal(in interface{}) (map[interface{}]interface{}, error) {
+	yamlBytes, err := yaml.Marshal(in)
+	if err != nil {
+		return nil, err
+	}
+
+	object := make(map[interface{}]interface{})
+	if err := yaml.Unmarshal(yamlBytes, object); err != nil {
+		return nil, err
+	}
+
+	return object, nil
+}
+
+func diffConfig(defaultConfig, actualConfig map[interface{}]interface{}) (map[interface{}]interface{}, error) {
+	output := make(map[interface{}]interface{})
+
+	for key, value := range actualConfig {
+
+		defaultValue, ok := defaultConfig[key]
+		if !ok {
+			output[key] = value
+			continue
 		}
 
-		w.Header().Set("Content-Type", "text/yaml")
-		w.WriteHeader(http.StatusOK)
-		if _, err := w.Write(out); err != nil {
-			level.Error(util.Logger).Log("msg", "error writing response", "err", err)
+		switch v := value.(type) {
+		case int:
+			defaultV, ok := defaultValue.(int)
+			if !ok || defaultV != v {
+				output[key] = v
+			}
+		case string:
+			defaultV, ok := defaultValue.(string)
+			if !ok || defaultV != v {
+				output[key] = v
+			}
+		case bool:
+			defaultV, ok := defaultValue.(bool)
+			if !ok || defaultV != v {
+				output[key] = v
+			}
+		case []interface{}:
+			defaultV, ok := defaultValue.([]interface{})
+			if !ok || !reflect.DeepEqual(defaultV, v) {
+				output[key] = v
+			}
+		case float64:
+			defaultV, ok := defaultValue.(float64)
+			if !ok || !reflect.DeepEqual(defaultV, v) {
+				output[key] = v
+			}
+		case map[interface{}]interface{}:
+			defaultV, ok := defaultValue.(map[interface{}]interface{})
+			if !ok {
+				output[key] = value
+			}
+			diff, err := diffConfig(defaultV, v)
+			if err != nil {
+				return nil, err
+			}
+			if len(diff) > 0 {
+				output[key] = diff
+			}
+		default:
+			return nil, fmt.Errorf("unsupported type %T", v)
 		}
 	}
+
+	return output, nil
+}
+
+func configHandler(actualCfg interface{}, defaultCfg interface{}) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		var output interface{}
+		switch r.URL.Query().Get("mode") {
+		case "diff":
+			defaultCfgObj, err := yamlMarshalUnmarshal(defaultCfg)
+			if err != nil {
+				http.Error(w, err.Error(), http.StatusInternalServerError)
+				return
+			}
+
+			actualCfgObj, err := yamlMarshalUnmarshal(actualCfg)
+			if err != nil {
+				http.Error(w, err.Error(), http.StatusInternalServerError)
+				return
+			}
+
+			diff, err := diffConfig(defaultCfgObj, actualCfgObj)
+			if err != nil {
+				http.Error(w, err.Error(), http.StatusInternalServerError)
+				return
+			}
+			output = diff
+
+		case "defaults":
+			output = defaultCfg
+		default:
+			output = actualCfg
+		}
+
+		util.WriteYAMLResponse(w, output)
+	}
 }
 
 // NewQuerierHandler returns a HTTP handler that can be used by the querier service to

pkg/api/handlers_test.go

@@ -1,10 +1,12 @@
 package api
 
 import (
+	"io/ioutil"
 	"net/http/httptest"
 	"strings"
 	"testing"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -53,3 +55,110 @@ func TestIndexPageContent(t *testing.T) {
 	require.True(t, strings.Contains(resp.Body.String(), "/shutdown"))
 	require.False(t, strings.Contains(resp.Body.String(), "/compactor/ring"))
 }
+
+type diffConfigMock struct {
+	MyInt          int          `yaml:"my_int"`
+	MyFloat        float64      `yaml:"my_float"`
+	MySlice        []string     `yaml:"my_slice"`
+	IgnoredField   func() error `yaml:"-"`
+	MyNestedStruct struct {
+		MyString      string   `yaml:"my_string"`
+		MyBool        bool     `yaml:"my_bool"`
+		MyEmptyStruct struct{} `yaml:"my_empty_struct"`
+	} `yaml:"my_nested_struct"`
+}
+
+func newDefaultDiffConfigMock() *diffConfigMock {
+	c := &diffConfigMock{
+		MyInt:        666,
+		MyFloat:      6.66,
+		MySlice:      []string{"value1", "value2"},
+		IgnoredField: func() error { return nil },
+	}
+	c.MyNestedStruct.MyString = "string1"
+	return c
+}
+
+func TestConfigDiffHandler(t *testing.T) {
+	for _, tc := range []struct {
+		name               string
+		expectedStatusCode int
+		expectedBody       string
+		actualConfig       func() interface{}
+	}{
+		{
+			name:               "no config parameters overridden",
+			expectedStatusCode: 200,
+			expectedBody:       "{}\n",
+		},
+		{
+			name: "slice changed",
+			actualConfig: func() interface{} {
+				c := newDefaultDiffConfigMock()
+				c.MySlice = append(c.MySlice, "value3")
+				return c
+			},
+			expectedStatusCode: 200,
+			expectedBody: "my_slice:\n" +
+				"- value1\n" +
+				"- value2\n" +
+				"- value3\n",
+		},
+		{
+			name: "string in nested struct changed",
+			actualConfig: func() interface{} {
+				c := newDefaultDiffConfigMock()
+				c.MyNestedStruct.MyString = "string2"
+				return c
+			},
+			expectedStatusCode: 200,
+			expectedBody: "my_nested_struct:\n" +
+				"  my_string: string2\n",
+		},
+		{
+			name: "bool in nested struct changed",
+			actualConfig: func() interface{} {
+				c := newDefaultDiffConfigMock()
+				c.MyNestedStruct.MyBool = true
+				return c
+			},
+			expectedStatusCode: 200,
+			expectedBody: "my_nested_struct:\n" +
+				"  my_bool: true\n",
+		},
+		{
+			name: "test invalid input",
+			actualConfig: func() interface{} {
+				c := "x"
+				return &c
+			},
+			expectedStatusCode: 500,
+			expectedBody: "yaml: unmarshal errors:\n" +
+				"  line 1: cannot unmarshal !!str `x` into map[interface {}]interface {}\n",
+		},
+	} {
+		defaultCfg := newDefaultDiffConfigMock()
+		t.Run(tc.name, func(t *testing.T) {
+
+			var actualCfg interface{}
+			if tc.actualConfig != nil {
+				actualCfg = tc.actualConfig()
+			} else {
+				actualCfg = newDefaultDiffConfigMock()
+			}
+
+			req := httptest.NewRequest("GET", "http://test.com/config?mode=diff", nil)
+			w := httptest.NewRecorder()
+
+			h := configHandler(actualCfg, defaultCfg)
+			h(w, req)
+			resp := w.Result()
+			assert.Equal(t, tc.expectedStatusCode, resp.StatusCode)
+
+			body, err := ioutil.ReadAll(resp.Body)
+			assert.NoError(t, err)
+			assert.Equal(t, tc.expectedBody, string(body))
+		})
+	}
+
+}

pkg/cortex/modules.go

@@ -1,6 +1,7 @@
 package cortex
 
 import (
+	"flag"
 	"fmt"
 	"os"
 	"time"
@@ -80,6 +81,13 @@ const (
 	All                      string = "all"
 )
 
+func newDefaultConfig() *Config {
+	defaultConfig := &Config{}
+	defaultFS := flag.NewFlagSet("", flag.PanicOnError)
+	defaultConfig.RegisterFlags(defaultFS)
+	return defaultConfig
+}
+
 func (t *Cortex) initAPI() (services.Service, error) {
 	t.Cfg.API.ServerPrefix = t.Cfg.Server.PathPrefix
 	t.Cfg.API.LegacyHTTPPrefix = t.Cfg.HTTPPrefix
@@ -90,8 +98,7 @@ func (t *Cortex) initAPI() (services.Service, error) {
 	}
 
 	t.API = a
-
-	t.API.RegisterAPI(t.Cfg.Server.PathPrefix, t.Cfg)
+	t.API.RegisterAPI(t.Cfg.Server.PathPrefix, t.Cfg, newDefaultConfig())
 
 	return nil, nil
 }