feat(remote): Implement lazy distributed feature (#64)

THIS IS AN EXPERIMENTAL FEATURE/IMPLEMENTATION, AND IT MAY BE REMOVED IN THE FUTURE.

Note that for now, it will be an undocumented feature.

config/config.go

@@ -10,6 +10,7 @@ import (
 	"github.com/TwiN/gatus/v4/alerting/alert"
 	"github.com/TwiN/gatus/v4/alerting/provider"
 	"github.com/TwiN/gatus/v4/config/maintenance"
+	"github.com/TwiN/gatus/v4/config/remote"
 	"github.com/TwiN/gatus/v4/config/ui"
 	"github.com/TwiN/gatus/v4/config/web"
 	"github.com/TwiN/gatus/v4/core"
@@ -85,6 +86,10 @@ type Config struct {
 	// Maintenance is the configuration for creating a maintenance window in which no alerts are sent
 	Maintenance *maintenance.Config `yaml:"maintenance,omitempty"`
 
+	// Remote is the configuration for remote Gatus instances
+	// WARNING: This is in ALPHA and may change or be completely removed in the future
+	Remote *remote.Config `yaml:"remote,omitempty"`
+
 	filePath        string    // path to the file from which config was loaded from
 	lastFileModTime time.Time // last modification time
 }
@@ -185,10 +190,22 @@ func parseAndValidateConfigBytes(yamlBytes []byte) (config *Config, err error) {
 		if err := validateStorageConfig(config); err != nil {
 			return nil, err
 		}
+		if err := validateRemoteConfig(config); err != nil {
+			return nil, err
+		}
 	}
 	return
 }
 
+func validateRemoteConfig(config *Config) error {
+	if config.Remote != nil {
+		if err := config.Remote.ValidateAndSetDefaults(); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 func validateStorageConfig(config *Config) error {
 	if config.Storage == nil {
 		config.Storage = &storage.Config{

config/remote/remote.go

@@ -0,0 +1,38 @@
+package remote
+
+import (
+	"log"
+
+	"github.com/TwiN/gatus/v4/client"
+)
+
+// NOTICE: This is an experimental alpha feature and may be updated/removed in future versions.
+// For more information, see https://github.com/TwiN/gatus/issues/64
+
+type Config struct {
+	// Instances is a list of remote instances to retrieve endpoint statuses from.
+	Instances []Instance `yaml:"instances,omitempty"`
+
+	// ClientConfig is the configuration of the client used to communicate with the provider's target
+	ClientConfig *client.Config `yaml:"client,omitempty"`
+}
+
+type Instance struct {
+	EndpointPrefix string `yaml:"endpoint-prefix"`
+	URL            string `yaml:"url"`
+}
+
+func (c *Config) ValidateAndSetDefaults() error {
+	if c.ClientConfig == nil {
+		c.ClientConfig = client.GetDefaultConfig()
+	} else {
+		if err := c.ClientConfig.ValidateAndSetDefaults(); err != nil {
+			return err
+		}
+	}
+	if len(c.Instances) > 0 {
+		log.Println("WARNING: Your configuration is using 'remote', which is in alpha and may be updated/removed in future versions.")
+		log.Println("WARNING: See https://github.com/TwiN/gatus/issues/64 for more information")
+	}
+	return nil
+}

controller/controller.go

@@ -8,10 +8,9 @@ import (
 	"os"
 	"time"
 
+	"github.com/TwiN/gatus/v4/config"
 	"github.com/TwiN/gatus/v4/config/ui"
-	"github.com/TwiN/gatus/v4/config/web"
 	"github.com/TwiN/gatus/v4/controller/handler"
-	"github.com/TwiN/gatus/v4/security"
 )
 
 var (
@@ -21,19 +20,19 @@ var (
 )
 
 // Handle creates the router and starts the server
-func Handle(securityConfig *security.Config, webConfig *web.Config, uiConfig *ui.Config, enableMetrics bool) {
-	var router http.Handler = handler.CreateRouter(ui.StaticFolder, securityConfig, uiConfig, enableMetrics)
+func Handle(cfg *config.Config) {
+	var router http.Handler = handler.CreateRouter(ui.StaticFolder, cfg)
 	if os.Getenv("ENVIRONMENT") == "dev" {
 		router = handler.DevelopmentCORS(router)
 	}
 	server = &http.Server{
-		Addr:         fmt.Sprintf("%s:%d", webConfig.Address, webConfig.Port),
+		Addr:         fmt.Sprintf("%s:%d", cfg.Web.Address, cfg.Web.Port),
 		Handler:      router,
 		ReadTimeout:  15 * time.Second,
 		WriteTimeout: 15 * time.Second,
 		IdleTimeout:  15 * time.Second,
 	}
-	log.Println("[controller][Handle] Listening on " + webConfig.SocketAddress())
+	log.Println("[controller][Handle] Listening on " + cfg.Web.SocketAddress())
 	if os.Getenv("ROUTER_TEST") == "true" {
 		return
 	}

controller/controller_test.go

@@ -32,7 +32,7 @@ func TestHandle(t *testing.T) {
 	_ = os.Setenv("ROUTER_TEST", "true")
 	_ = os.Setenv("ENVIRONMENT", "dev")
 	defer os.Clearenv()
-	Handle(cfg.Security, cfg.Web, cfg.UI, cfg.Metrics)
+	Handle(cfg)
 	defer Shutdown()
 	request, _ := http.NewRequest("GET", "/health", http.NoBody)
 	responseRecorder := httptest.NewRecorder()

controller/handler/badge_test.go

@@ -31,7 +31,7 @@ func TestBadge(t *testing.T) {
 	}
 	watchdog.UpdateEndpointStatuses(cfg.Endpoints[0], &core.Result{Success: true, Connected: true, Duration: time.Millisecond, Timestamp: time.Now()})
 	watchdog.UpdateEndpointStatuses(cfg.Endpoints[1], &core.Result{Success: false, Connected: false, Duration: time.Second, Timestamp: time.Now()})
-	router := CreateRouter("../../web/static", cfg.Security, nil, cfg.Metrics)
+	router := CreateRouter("../../web/static", cfg)
 	type Scenario struct {
 		Name         string
 		Path         string

controller/handler/chart_test.go

@@ -30,7 +30,7 @@ func TestResponseTimeChart(t *testing.T) {
 	}
 	watchdog.UpdateEndpointStatuses(cfg.Endpoints[0], &core.Result{Success: true, Duration: time.Millisecond, Timestamp: time.Now()})
 	watchdog.UpdateEndpointStatuses(cfg.Endpoints[1], &core.Result{Success: false, Duration: time.Second, Timestamp: time.Now()})
-	router := CreateRouter("../../web/static", cfg.Security, nil, cfg.Metrics)
+	router := CreateRouter("../../web/static", cfg)
 	type Scenario struct {
 		Name         string
 		Path         string

controller/handler/endpoint_status.go

@@ -5,11 +5,16 @@ import (
 	"compress/gzip"
 	"encoding/json"
 	"fmt"
+	"io"
 	"log"
 	"net/http"
 	"strings"
 	"time"
 
+	"github.com/TwiN/gatus/v4/client"
+	"github.com/TwiN/gatus/v4/config"
+	"github.com/TwiN/gatus/v4/config/remote"
+	"github.com/TwiN/gatus/v4/core"
 	"github.com/TwiN/gatus/v4/storage/store"
 	"github.com/TwiN/gatus/v4/storage/store/common"
 	"github.com/TwiN/gatus/v4/storage/store/common/paging"
@@ -28,7 +33,8 @@ var (
 // EndpointStatuses handles requests to retrieve all EndpointStatus
 // Due to the size of the response, this function leverages a cache.
 // Must not be wrapped by GzipHandler
-func EndpointStatuses(writer http.ResponseWriter, r *http.Request) {
+func EndpointStatuses(cfg *config.Config) http.HandlerFunc {
+	return func(writer http.ResponseWriter, r *http.Request) {
 		page, pageSize := extractPageAndPageSizeFromRequest(r)
 		gzipped := strings.Contains(r.Header.Get("Accept-Encoding"), "gzip")
 		var exists bool
@@ -50,6 +56,13 @@ func EndpointStatuses(writer http.ResponseWriter, r *http.Request) {
 				http.Error(writer, err.Error(), http.StatusInternalServerError)
 				return
 			}
+			// ALPHA: Retrieve endpoint statuses from remote instances
+			if endpointStatusesFromRemote, err := getEndpointStatusesFromRemoteInstances(cfg.Remote); err != nil {
+				log.Printf("[handler][EndpointStatuses] Silently failed to retrieve endpoint statuses from remote: %s", err.Error())
+			} else if endpointStatusesFromRemote != nil {
+				endpointStatuses = append(endpointStatuses, endpointStatusesFromRemote...)
+			}
+			// Marshal endpoint statuses to JSON
 			data, err = json.Marshal(endpointStatuses)
 			if err != nil {
 				log.Printf("[handler][EndpointStatuses] Unable to marshal object to JSON: %s", err.Error())
@@ -71,6 +84,39 @@ func EndpointStatuses(writer http.ResponseWriter, r *http.Request) {
 		writer.WriteHeader(http.StatusOK)
 		_, _ = writer.Write(data)
 	}
+}
+
+func getEndpointStatusesFromRemoteInstances(remoteConfig *remote.Config) ([]*core.EndpointStatus, error) {
+	if remoteConfig == nil || len(remoteConfig.Instances) == 0 {
+		return nil, nil
+	}
+	var endpointStatusesFromAllRemotes []*core.EndpointStatus
+	httpClient := client.GetHTTPClient(remoteConfig.ClientConfig)
+	for _, instance := range remoteConfig.Instances {
+		response, err := httpClient.Get(instance.URL)
+		if err != nil {
+			return nil, err
+		}
+		body, err := io.ReadAll(response.Body)
+		if err != nil {
+			_ = response.Body.Close()
+			log.Printf("[handler][getEndpointStatusesFromRemoteInstances] Silently failed to retrieve endpoint statuses from %s: %s", instance.URL, err.Error())
+			continue
+		}
+		var endpointStatuses []*core.EndpointStatus
+		if err = json.Unmarshal(body, &endpointStatuses); err != nil {
+			_ = response.Body.Close()
+			log.Printf("[handler][getEndpointStatusesFromRemoteInstances] Silently failed to retrieve endpoint statuses from %s: %s", instance.URL, err.Error())
+			continue
+		}
+		_ = response.Body.Close()
+		for _, endpointStatus := range endpointStatuses {
+			endpointStatus.Name = instance.EndpointPrefix + endpointStatus.Name
+		}
+		endpointStatusesFromAllRemotes = append(endpointStatusesFromAllRemotes, endpointStatuses...)
+	}
+	return endpointStatusesFromAllRemotes, nil
+}
 
 // EndpointStatus retrieves a single core.EndpointStatus by group and endpoint name
 func EndpointStatus(writer http.ResponseWriter, r *http.Request) {

controller/handler/endpoint_status_test.go

@@ -97,7 +97,7 @@ func TestEndpointStatus(t *testing.T) {
 	}
 	watchdog.UpdateEndpointStatuses(cfg.Endpoints[0], &core.Result{Success: true, Duration: time.Millisecond, Timestamp: time.Now()})
 	watchdog.UpdateEndpointStatuses(cfg.Endpoints[1], &core.Result{Success: false, Duration: time.Second, Timestamp: time.Now()})
-	router := CreateRouter("../../web/static", cfg.Security, nil, cfg.Metrics)
+	router := CreateRouter("../../web/static", cfg)
 
 	type Scenario struct {
 		Name         string
@@ -153,7 +153,7 @@ func TestEndpointStatuses(t *testing.T) {
 	// Can't be bothered dealing with timezone issues on the worker that runs the automated tests
 	firstResult.Timestamp = time.Time{}
 	secondResult.Timestamp = time.Time{}
-	router := CreateRouter("../../web/static", nil, nil, false)
+	router := CreateRouter("../../web/static", &config.Config{Metrics: true})
 
 	type Scenario struct {
 		Name         string

controller/handler/favicon_test.go

@@ -4,10 +4,12 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"testing"
+
+	"github.com/TwiN/gatus/v4/config"
 )
 
 func TestFavIcon(t *testing.T) {
-	router := CreateRouter("../../web/static", nil, nil, false)
+	router := CreateRouter("../../web/static", &config.Config{})
 	type Scenario struct {
 		Name         string
 		Path         string

controller/handler/handler.go

@@ -3,32 +3,31 @@ package handler
 import (
 	"net/http"
 
-	"github.com/TwiN/gatus/v4/config/ui"
-	"github.com/TwiN/gatus/v4/security"
+	"github.com/TwiN/gatus/v4/config"
 	"github.com/TwiN/health"
 	"github.com/gorilla/mux"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
 )
 
-func CreateRouter(staticFolder string, securityConfig *security.Config, uiConfig *ui.Config, enabledMetrics bool) *mux.Router {
+func CreateRouter(staticFolder string, cfg *config.Config) *mux.Router {
 	router := mux.NewRouter()
-	if enabledMetrics {
+	if cfg.Metrics {
 		router.Handle("/metrics", promhttp.Handler()).Methods("GET")
 	}
 	api := router.PathPrefix("/api").Subrouter()
 	protected := api.PathPrefix("/").Subrouter()
 	unprotected := api.PathPrefix("/").Subrouter()
-	if securityConfig != nil {
-		if err := securityConfig.RegisterHandlers(router); err != nil {
+	if cfg.Security != nil {
+		if err := cfg.Security.RegisterHandlers(router); err != nil {
 			panic(err)
 		}
-		if err := securityConfig.ApplySecurityMiddleware(protected); err != nil {
+		if err := cfg.Security.ApplySecurityMiddleware(protected); err != nil {
 			panic(err)
 		}
 	}
 	// Endpoints
-	unprotected.Handle("/v1/config", ConfigHandler{securityConfig: securityConfig}).Methods("GET")
-	protected.HandleFunc("/v1/endpoints/statuses", EndpointStatuses).Methods("GET") // No GzipHandler for this one, because we cache the content as Gzipped already
+	unprotected.Handle("/v1/config", ConfigHandler{securityConfig: cfg.Security}).Methods("GET")
+	protected.HandleFunc("/v1/endpoints/statuses", EndpointStatuses(cfg)).Methods("GET") // No GzipHandler for this one, because we cache the content as Gzipped already
 	protected.HandleFunc("/v1/endpoints/{key}/statuses", GzipHandlerFunc(EndpointStatus)).Methods("GET")
 	unprotected.HandleFunc("/v1/endpoints/{key}/health/badge.svg", HealthBadge).Methods("GET")
 	unprotected.HandleFunc("/v1/endpoints/{key}/uptimes/{duration}/badge.svg", UptimeBadge).Methods("GET")
@@ -38,8 +37,8 @@ func CreateRouter(staticFolder string, securityConfig *security.Config, uiConfig
 	router.Handle("/health", health.Handler().WithJSON(true)).Methods("GET")
 	router.HandleFunc("/favicon.ico", FavIcon(staticFolder)).Methods("GET")
 	// SPA
-	router.HandleFunc("/endpoints/{name}", SinglePageApplication(staticFolder, uiConfig)).Methods("GET")
-	router.HandleFunc("/", SinglePageApplication(staticFolder, uiConfig)).Methods("GET")
+	router.HandleFunc("/endpoints/{name}", SinglePageApplication(staticFolder, cfg.UI)).Methods("GET")
+	router.HandleFunc("/", SinglePageApplication(staticFolder, cfg.UI)).Methods("GET")
 	// Everything else falls back on static content
 	router.PathPrefix("/").Handler(GzipHandler(http.FileServer(http.Dir(staticFolder))))
 	return router

controller/handler/handler_test.go

@@ -4,10 +4,12 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"testing"
+
+	"github.com/TwiN/gatus/v4/config"
 )
 
 func TestCreateRouter(t *testing.T) {
-	router := CreateRouter("../../web/static", nil, nil, true)
+	router := CreateRouter("../../web/static", &config.Config{Metrics: true})
 	type Scenario struct {
 		Name         string
 		Path         string

controller/handler/spa_test.go

@@ -30,7 +30,7 @@ func TestSinglePageApplication(t *testing.T) {
 	}
 	watchdog.UpdateEndpointStatuses(cfg.Endpoints[0], &core.Result{Success: true, Duration: time.Millisecond, Timestamp: time.Now()})
 	watchdog.UpdateEndpointStatuses(cfg.Endpoints[1], &core.Result{Success: false, Duration: time.Second, Timestamp: time.Now()})
-	router := CreateRouter("../../web/static", cfg.Security, nil, cfg.Metrics)
+	router := CreateRouter("../../web/static", cfg)
 	type Scenario struct {
 		Name         string
 		Path         string

main.go

@@ -36,7 +36,7 @@ func main() {
 }
 
 func start(cfg *config.Config) {
-	go controller.Handle(cfg.Security, cfg.Web, cfg.UI, cfg.Metrics)
+	go controller.Handle(cfg)
 	watchdog.Monitor(cfg)
 	go listenToConfigurationFileChanges(cfg)
 }