Expose current Prometheus config via /status/config

This PR adds the `/status/config` endpoint which exposes the currently
loaded Prometheus config. This is the same config that is displayed on
`/config` in the UI in YAML format. The response payload looks like
such:
```
{
  "status": "success",
  "data": {
    "yaml": <CONFIG>
  }
}
```

config/config_test.go

@@ -540,15 +540,27 @@ func TestLoadConfig(t *testing.T) {
 	if !reflect.DeepEqual(c, expectedConf) {
 		t.Fatalf("%s: unexpected config result: \n\n%s\n expected\n\n%s", "testdata/conf.good.yml", bgot, bexp)
 	}
-
-	// String method must not reveal authentication credentials.
-	s := c.String()
-	secretRe := regexp.MustCompile("<secret>")
-	matches := secretRe.FindAllStringIndex(s, -1)
-	if len(matches) != 6 || strings.Contains(s, "mysecret") {
-		t.Fatalf("config's String method reveals authentication credentials.")
 }
 
+// YAML marshalling must not reveal authentication credentials.
+func TestElideSecrets(t *testing.T) {
+	c, err := LoadFile("testdata/conf.good.yml")
+	if err != nil {
+		t.Fatalf("Error parsing %s: %s", "testdata/conf.good.yml", err)
+	}
+
+	secretRe := regexp.MustCompile(`\\u003csecret\\u003e|<secret>`)
+
+	config, err := yaml.Marshal(c)
+	if err != nil {
+		t.Fatal(err)
+	}
+	yamlConfig := string(config)
+
+	matches := secretRe.FindAllStringIndex(yamlConfig, -1)
+	if len(matches) != 6 || strings.Contains(yamlConfig, "mysecret") {
+		t.Fatalf("yaml marshal reveals authentication credentials.")
+	}
 }
 
 func TestLoadConfigRuleFilesAbsolutePath(t *testing.T) {

web/api/v1/api.go

@@ -29,6 +29,7 @@ import (
 	"github.com/prometheus/common/route"
 	"golang.org/x/net/context"
 
+	"github.com/prometheus/prometheus/config"
 	"github.com/prometheus/prometheus/promql"
 	"github.com/prometheus/prometheus/retrieval"
 	"github.com/prometheus/prometheus/storage/local"
@@ -104,16 +105,18 @@ type API struct {
 	alertmanagerRetriever alertmanagerRetriever
 
 	now    func() model.Time
+	config func() config.Config
 }
 
 // NewAPI returns an initialized API type.
-func NewAPI(qe *promql.Engine, st local.Storage, tr targetRetriever, ar alertmanagerRetriever) *API {
+func NewAPI(qe *promql.Engine, st local.Storage, tr targetRetriever, ar alertmanagerRetriever, configFunc func() config.Config) *API {
 	return &API{
 		QueryEngine:           qe,
 		Storage:               st,
 		targetRetriever:       tr,
 		alertmanagerRetriever: ar,
 		now:    model.Now,
+		config: configFunc,
 	}
 }
 
@@ -147,6 +150,8 @@ func (api *API) Register(r *route.Router) {
 
 	r.Get("/targets", instr("targets", api.targets))
 	r.Get("/alertmanagers", instr("alertmanagers", api.alertmanagers))
+
+	r.Get("/status/config", instr("config", api.serveConfig))
 }
 
 type queryData struct {
@@ -436,6 +441,17 @@ func (api *API) alertmanagers(r *http.Request) (interface{}, *apiError) {
 	return ams, nil
 }
 
+type prometheusConfig struct {
+	YAML string `json:"yaml"`
+}
+
+func (api *API) serveConfig(r *http.Request) (interface{}, *apiError) {
+	cfg := &prometheusConfig{
+		YAML: api.config().String(),
+	}
+	return cfg, nil
+}
+
 func respond(w http.ResponseWriter, data interface{}) {
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(http.StatusOK)

web/api/v1/api_test.go

@@ -29,6 +29,7 @@ import (
 	"github.com/prometheus/common/route"
 	"golang.org/x/net/context"
 
+	"github.com/prometheus/prometheus/config"
 	"github.com/prometheus/prometheus/promql"
 	"github.com/prometheus/prometheus/retrieval"
 )
@@ -45,6 +46,15 @@ func (f alertmanagerRetrieverFunc) Alertmanagers() []*url.URL {
 	return f()
 }
 
+var samplePrometheusCfg = config.Config{
+	GlobalConfig:       config.GlobalConfig{},
+	AlertingConfig:     config.AlertingConfig{},
+	RuleFiles:          []string{},
+	ScrapeConfigs:      []*config.ScrapeConfig{},
+	RemoteWriteConfigs: []*config.RemoteWriteConfig{},
+	RemoteReadConfigs:  []*config.RemoteReadConfig{},
+}
+
 func TestEndpoints(t *testing.T) {
 	suite, err := promql.NewTest(t, `
 		load 1m
@@ -91,6 +101,9 @@ func TestEndpoints(t *testing.T) {
 		targetRetriever:       tr,
 		alertmanagerRetriever: ar,
 		now: func() model.Time { return now },
+		config: func() config.Config {
+			return samplePrometheusCfg
+		},
 	}
 
 	start := model.Time(0)
@@ -445,7 +458,8 @@ func TestEndpoints(t *testing.T) {
 					"foo":      "bar",
 				},
 			},
-		}, {
+		},
+		{
 			endpoint: api.dropSeries,
 			query: url.Values{
 				"match[]": []string{`{__name__=~".+"}`},
@@ -453,7 +467,8 @@ func TestEndpoints(t *testing.T) {
 			response: struct {
 				NumDeleted int `json:"numDeleted"`
 			}{2},
-		}, {
+		},
+		{
 			endpoint: api.targets,
 			response: &TargetDiscovery{
 				ActiveTargets: []*Target{
@@ -465,7 +480,8 @@ func TestEndpoints(t *testing.T) {
 					},
 				},
 			},
-		}, {
+		},
+		{
 			endpoint: api.alertmanagers,
 			response: &AlertmanagerDiscovery{
 				ActiveAlertmanagers: []*AlertmanagerTarget{
@@ -475,6 +491,12 @@ func TestEndpoints(t *testing.T) {
 				},
 			},
 		},
+		{
+			endpoint: api.serveConfig,
+			response: &prometheusConfig{
+				YAML: samplePrometheusCfg.String(),
+			},
+		},
 	}
 
 	for _, test := range tests {

web/federate.go

@@ -74,7 +74,7 @@ func (h *Handler) federation(w http.ResponseWriter, req *http.Request) {
 	}
 	sort.Sort(byName(vector))
 
-	externalLabels := h.externalLabels.Clone()
+	externalLabels := h.config.GlobalConfig.ExternalLabels.Clone()
 	if _, ok := externalLabels[model.InstanceLabel]; !ok {
 		externalLabels[model.InstanceLabel] = ""
 	}

web/federate_test.go

@@ -23,6 +23,7 @@ import (
 	"testing"
 
 	"github.com/prometheus/common/model"
+	"github.com/prometheus/prometheus/config"
 	"github.com/prometheus/prometheus/promql"
 )
 
@@ -178,10 +179,13 @@ func TestFederation(t *testing.T) {
 		storage:     suite.Storage(),
 		queryEngine: suite.QueryEngine(),
 		now:         func() model.Time { return 101 * 60 * 1000 }, // 101min after epoch.
+		config: &config.Config{
+			GlobalConfig: config.GlobalConfig{},
+		},
 	}
 
 	for name, scenario := range scenarios {
-		h.externalLabels = scenario.externalLabels
+		h.config.GlobalConfig.ExternalLabels = scenario.externalLabels
 		req, err := http.ReadRequest(bufio.NewReader(strings.NewReader(
 			"GET http://example.org/federate?" + scenario.params + " HTTP/1.0\r\n\r\n",
 		)))

web/web.go

@@ -73,26 +73,24 @@ type Handler struct {
 	quitCh      chan struct{}
 	reloadCh    chan chan error
 	options     *Options
-	configString string
+	config      *config.Config
 	versionInfo *PrometheusVersion
 	birth       time.Time
 	cwd         string
 	flagsMap    map[string]string
 
-	externalLabels model.LabelSet
 	mtx sync.RWMutex
 	now func() model.Time
 
 	ready uint32 // ready is uint32 rather than boolean to be able to use atomic functions.
 }
 
-// ApplyConfig updates the status state as the new config requires.
+// ApplyConfig updates the config field of the Handler struct
 func (h *Handler) ApplyConfig(conf *config.Config) error {
 	h.mtx.Lock()
 	defer h.mtx.Unlock()
 
-	h.externalLabels = conf.GlobalConfig.ExternalLabels
-	h.configString = conf.String()
+	h.config = conf
 
 	return nil
 }
@@ -158,12 +156,23 @@ func New(o *Options) *Handler {
 		storage:       o.Storage,
 		notifier:      o.Notifier,
 
-		apiV1: api_v1.NewAPI(o.QueryEngine, o.Storage, o.TargetManager, o.Notifier),
 		now: model.Now,
 
 		ready: 0,
 	}
 
+	h.apiV1 = api_v1.NewAPI(
+		o.QueryEngine,
+		o.Storage,
+		o.TargetManager,
+		o.Notifier,
+		func() config.Config {
+			h.mtx.RLock()
+			defer h.mtx.RUnlock()
+			return *h.config
+		},
+	)
+
 	if o.RoutePrefix != "/" {
 		// If the prefix is missing for the root path, prepend it.
 		router.Get("/", func(w http.ResponseWriter, r *http.Request) {
@@ -184,7 +193,7 @@ func New(o *Options) *Handler {
 	router.Get("/graph", readyf(instrf("graph", h.graph)))
 	router.Get("/status", readyf(instrf("status", h.status)))
 	router.Get("/flags", readyf(instrf("flags", h.flags)))
-	router.Get("/config", readyf(instrf("config", h.config)))
+	router.Get("/config", readyf(instrf("config", h.serveConfig)))
 	router.Get("/rules", readyf(instrf("rules", h.rules)))
 	router.Get("/targets", readyf(instrf("targets", h.targets)))
 	router.Get("/version", readyf(instrf("version", h.version)))
@@ -404,11 +413,11 @@ func (h *Handler) flags(w http.ResponseWriter, r *http.Request) {
 	h.executeTemplate(w, "flags.html", h.flagsMap)
 }
 
-func (h *Handler) config(w http.ResponseWriter, r *http.Request) {
+func (h *Handler) serveConfig(w http.ResponseWriter, r *http.Request) {
 	h.mtx.RLock()
 	defer h.mtx.RUnlock()
 
-	h.executeTemplate(w, "config.html", h.configString)
+	h.executeTemplate(w, "config.html", h.config.String())
 }
 
 func (h *Handler) rules(w http.ResponseWriter, r *http.Request) {