fix: add HTTP backend readiness probes (#97)

README.md

@@ -167,6 +167,7 @@ You can still use the non-prefixed environment variables in the spirit of the ba
 | `HOST_GRAPHQL`            | The host to proxy the graphql endpoint   | `http://localhost/` |
 | `HOST_GRAPHQL_READONLY`   | The host to proxy the read-only graphql endpoint | ``               |
 | `HEALTHCHECK_GRAPHQL_URL` | The URL to check the health of the graphql endpoint | `` |
+| `BACKEND_HEALTHCHECK_URL` | Optional HTTP readiness URL for startup and periodic backend checks; empty keeps the GraphQL probe | `` |
 | `JWT_USER_CLAIM_PATH`     | Path to the user claim in the JWT token  | ``                         |
 | `JWT_ROLE_CLAIM_PATH`     | Path to the role claim in the JWT token  | ``                         |
 | `JWT_VERIFY_SIGNATURE`    | Verify the JWT signature before trusting its claims (see [Caching](#caching)) | `false` |
@@ -1127,6 +1128,12 @@ With the `PURGE_METRICS_ON_CRAWL` enabled, the `graphql_proxy_requests_failed`,
 
 If you'd like the `/healthz` endpoint to perform actual check for the connectivity to the graphql endpoint - set the `HEALTHCHECK_GRAPHQL_URL` environment variable to the exact URL of the graphql endpoint. The query executed will be `query { __typename }` and if the response is not `200 OK` - the healthcheck will fail. Remember that the endpoint is a full URL which you'd like to check, so it should include the protocol, host and path - for example `http://localhost:8080/v1/graphql` and it's NOT the same as value of `HOST_GRAPHQL` environment variable which should provide only the host, without path, ending with slash.
 
+`BACKEND_HEALTHCHECK_URL` controls a separate check: the backend health manager's startup and periodic probes. Set it to an unauthenticated readiness endpoint, for example `http://127.0.0.1:8080/ready`. The manager sends `GET` to the supplied path and query, without a GraphQL body or authentication headers. Any 2xx response is healthy; network errors, timeouts, and other status codes are unhealthy. The request timeout remains five seconds, and redirects are not followed.
+
+When this variable is empty, the manager continues to send an unauthenticated `POST` containing `{"query":"{__typename}"}` to `HOST_GRAPHQL`. It preserves a supplied path, or appends `/v1/graphql` when there is no path beyond `/`. A configured readiness URL must use HTTP or HTTPS with a nonempty host and no userinfo or fragment. Invalid configuration stops startup; it does not fall back to GraphQL. Do not put secrets in the URL: probe targets are logged.
+
+This setting does not change `HEALTHCHECK_GRAPHQL_URL`, the API `/healthz` check, GraphQL authorization, or headers on forwarded client requests. Keep the GraphQL endpoint protected; only the readiness endpoint must accept these unauthenticated probes.
+
 #### Monitoring endpoint
 
 Example metrics produced by the proxy:

api_health_test.go

@@ -62,7 +62,7 @@ func TestApiBackendHealth_HealthyManager_Returns200(t *testing.T) {
 	defer func() { backendHealthManager = orig }()
 
 	// inject a healthy manager directly (bypassing sync.Once)
-	mgr := NewBackendHealthManager(&fasthttp.Client{}, "http://localhost:8080", libpack_logger.New())
+	mgr := NewBackendHealthManager(&fasthttp.Client{}, "http://localhost:8080", "", libpack_logger.New())
 	mgr.isHealthy.Store(true)
 	backendHealthManager = mgr
 
@@ -86,7 +86,7 @@ func TestApiBackendHealth_UnhealthyManager_Returns503(t *testing.T) {
 	orig := backendHealthManager
 	defer func() { backendHealthManager = orig }()
 
-	mgr := NewBackendHealthManager(&fasthttp.Client{}, "http://localhost:8080", libpack_logger.New())
+	mgr := NewBackendHealthManager(&fasthttp.Client{}, "http://localhost:8080", "", libpack_logger.New())
 	mgr.isHealthy.Store(false)
 	backendHealthManager = mgr
 

backend_health.go

@@ -22,6 +22,8 @@ type BackendHealthManager struct {
 	logger           *libpack_logger.Logger
 	cancel           context.CancelFunc
 	backendURL       string
+	healthCheckURL   string
+	useHTTPReadiness bool
 	checkInterval    time.Duration
 	maxRetries       int
 	mu               sync.RWMutex
@@ -32,11 +34,34 @@ type BackendHealthManager struct {
 }
 
 // NewBackendHealthManager creates a new backend health manager
-func NewBackendHealthManager(client *fasthttp.Client, backendURL string, logger *libpack_logger.Logger) *BackendHealthManager {
+func NewBackendHealthManager(client *fasthttp.Client, backendURL, readinessURL string, logger *libpack_logger.Logger) *BackendHealthManager {
 	ctx, cancel := context.WithCancel(context.Background())
+	healthCheckURL := readinessURL
+	if healthCheckURL == "" {
+		healthCheckURL = backendGraphQLHealthURL(backendURL)
+	} else {
+		// Path normalization is a client setting in fasthttp. Use a separate
+		// pool so readiness URLs stay exact without changing forwarded traffic.
+		client = &fasthttp.Client{
+			Dial:                     client.Dial,
+			DialTimeout:              client.DialTimeout,
+			TLSConfig:                client.TLSConfig,
+			ReadTimeout:              client.ReadTimeout,
+			WriteTimeout:             client.WriteTimeout,
+			MaxIdleConnDuration:      client.MaxIdleConnDuration,
+			MaxConnDuration:          client.MaxConnDuration,
+			ReadBufferSize:           client.ReadBufferSize,
+			WriteBufferSize:          client.WriteBufferSize,
+			MaxResponseBodySize:      client.MaxResponseBodySize,
+			NoDefaultUserAgentHeader: client.NoDefaultUserAgentHeader,
+			DisablePathNormalizing:   true,
+		}
+	}
 	return &BackendHealthManager{
 		client:           client,
 		backendURL:       backendURL,
+		healthCheckURL:   healthCheckURL,
+		useHTTPReadiness: readinessURL != "",
 		checkInterval:    5 * time.Second,
 		maxRetries:       30, // 30 * 5s = 2.5 minutes max startup wait
 		ctx:              ctx,
@@ -59,6 +84,7 @@ func (bhm *BackendHealthManager) WaitForBackendReady(timeout time.Duration) erro
 		Message: "Waiting for GraphQL backend to become ready",
 		Pairs: map[string]any{
 			"backend_url": bhm.backendURL,
+			"check_url":   bhm.healthCheckURL,
 			"timeout":     timeout.String(),
 		},
 	})
@@ -149,42 +175,14 @@ func (bhm *BackendHealthManager) checkBackendHealth() bool {
 	defer fasthttp.ReleaseRequest(req)
 	defer fasthttp.ReleaseResponse(resp)
 
-	// Determine the health check URL
-	// If backendURL is just "http://host:port" or "http://host:port/", append /v1/graphql
-	// If it has a path like "/v1/graphql", use that path
-	healthCheckURL := bhm.backendURL
-	hasGraphQLPath := false
-
-	if len(bhm.backendURL) > 0 {
-		// Simple check: if URL has a path component beyond just "/"
-		lastSlash := -1
-		protoEnd := 0
-		if idx := strings.Index(bhm.backendURL, "://"); idx >= 0 {
-			protoEnd = idx + 3
-		}
-		for i := protoEnd; i < len(bhm.backendURL); i++ {
-			if bhm.backendURL[i] == '/' {
-				lastSlash = i
-				break
-			}
-		}
-		// Has path if there's a slash after protocol and it's not the last char or followed by more path
-		hasGraphQLPath = lastSlash >= protoEnd && lastSlash < len(bhm.backendURL)-1
-
-		// If no GraphQL path, append /v1/graphql (standard Hasura endpoint)
-		if !hasGraphQLPath {
-			// Remove trailing slash if present
-			baseURL := strings.TrimSuffix(bhm.backendURL, "/")
-			healthCheckURL = baseURL + "/v1/graphql"
-		}
-	}
-
-	// Always send GraphQL introspection query for health check
-	healthQuery := `{"query":"{__typename}"}`
-	req.SetRequestURI(healthCheckURL)
+	req.SetRequestURI(bhm.healthCheckURL)
+	if bhm.useHTTPReadiness {
+		req.Header.SetMethod(http.MethodGet)
+	} else {
 		req.Header.SetMethod(http.MethodPost)
 		req.Header.SetContentType("application/json")
-	req.SetBody([]byte(healthQuery))
+		req.SetBodyString(`{"query":"{__typename}"}`)
+	}
 
 	// Short timeout for health checks
 	err := bhm.client.DoTimeout(req, resp, 5*time.Second)
@@ -193,7 +191,7 @@ func (bhm *BackendHealthManager) checkBackendHealth() bool {
 			Message: "Backend health check failed",
 			Pairs: map[string]any{
 				"error":     err.Error(),
-				"check_url": healthCheckURL,
+				"check_url": bhm.healthCheckURL,
 			},
 		})
 		return false
@@ -207,7 +205,7 @@ func (bhm *BackendHealthManager) checkBackendHealth() bool {
 			Message: "Backend returned unhealthy status",
 			Pairs: map[string]any{
 				"status_code": statusCode,
-				"check_url":   healthCheckURL,
+				"check_url":   bhm.healthCheckURL,
 			},
 		})
 	}
@@ -284,6 +282,9 @@ func (bhm *BackendHealthManager) Shutdown() {
 		return
 	}
 	bhm.cancel()
+	if bhm.useHTTPReadiness {
+		bhm.client.CloseIdleConnections()
+	}
 	if bhm.logger != nil {
 		bhm.logger.Info(&libpack_logger.LogMessage{
 			Message: "Backend health manager shut down",
@@ -298,9 +299,9 @@ var (
 )
 
 // InitializeBackendHealth initializes the backend health manager
-func InitializeBackendHealth(client *fasthttp.Client, backendURL string, logger *libpack_logger.Logger) *BackendHealthManager {
+func InitializeBackendHealth(client *fasthttp.Client, backendURL, readinessURL string, logger *libpack_logger.Logger) *BackendHealthManager {
 	backendHealthOnce.Do(func() {
-		backendHealthManager = NewBackendHealthManager(client, backendURL, logger)
+		backendHealthManager = NewBackendHealthManager(client, backendURL, readinessURL, logger)
 	})
 	return backendHealthManager
 }
@@ -309,3 +310,17 @@ func InitializeBackendHealth(client *fasthttp.Client, backendURL string, logger
 func GetBackendHealthManager() *BackendHealthManager {
 	return backendHealthManager
 }
+
+func backendGraphQLHealthURL(backendURL string) string {
+	if backendURL == "" {
+		return ""
+	}
+	protoEnd := 0
+	if idx := strings.Index(backendURL, "://"); idx >= 0 {
+		protoEnd = idx + 3
+	}
+	if pathStart := strings.IndexByte(backendURL[protoEnd:], '/'); pathStart >= 0 && protoEnd+pathStart < len(backendURL)-1 {
+		return backendURL
+	}
+	return strings.TrimSuffix(backendURL, "/") + "/v1/graphql"
+}

backend_health_test.go

@@ -0,0 +1,234 @@
+package main
+
+import (
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"os"
+	"os/exec"
+	"strings"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	libpack_logger "github.com/lukaszraczylo/graphql-monitoring-proxy/logging"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/valyala/fasthttp"
+)
+
+func TestBackendReadinessProtectedGraphQL(t *testing.T) {
+	var readyStatus atomic.Int32
+	readyStatus.Store(http.StatusOK)
+	var graphqlCalls atomic.Int32
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch r.URL.Path {
+		case "/v1/graphql":
+			graphqlCalls.Add(1)
+			w.WriteHeader(http.StatusUnauthorized)
+		case "/ready":
+			assert.Equal(t, http.MethodGet, r.Method)
+			assert.Empty(t, r.Header.Get("Authorization"))
+			assert.Empty(t, r.Header.Get("X-Husaria-Admin-Secret"))
+			assert.Empty(t, r.Header.Get("X-Hasura-Admin-Secret"))
+			body, err := io.ReadAll(r.Body)
+			assert.NoError(t, err)
+			assert.Empty(t, body)
+			w.WriteHeader(int(readyStatus.Load()))
+		default:
+			w.WriteHeader(http.StatusNotFound)
+		}
+	}))
+	t.Cleanup(server.Close)
+	client := &fasthttp.Client{}
+	t.Cleanup(client.CloseIdleConnections)
+	logger := libpack_logger.New().SetOutput(io.Discard)
+	legacy := NewBackendHealthManager(client, server.URL, "", logger)
+	t.Cleanup(legacy.Shutdown)
+	require.False(t, legacy.checkBackendHealth(), "GraphQL must reject the unauthenticated probe")
+
+	manager := NewBackendHealthManager(client, server.URL, server.URL+"/ready", logger)
+	t.Cleanup(manager.Shutdown)
+	manager.checkInterval = 10 * time.Millisecond
+	manager.StartHealthChecking()
+	require.NoError(t, manager.WaitForBackendReady(time.Second))
+	require.True(t, manager.IsHealthy())
+
+	readyStatus.Store(http.StatusServiceUnavailable)
+	require.Eventually(t, func() bool { return !manager.IsHealthy() }, time.Second, 5*time.Millisecond)
+	readyStatus.Store(http.StatusOK)
+	require.Eventually(t, manager.IsHealthy, time.Second, 5*time.Millisecond)
+	assert.Equal(t, int32(1), graphqlCalls.Load(), "readiness checks must not query protected GraphQL")
+	require.False(t, legacy.checkBackendHealth(), "readiness must not bypass GraphQL authorization")
+}
+
+func TestBackendReadinessExactTarget(t *testing.T) {
+	const target = "/checks//ready%2Fdatabase?probe=one%2Ftwo&probe=three"
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assert.Equal(t, http.MethodGet, r.Method)
+		assert.Equal(t, target, r.RequestURI)
+		w.WriteHeader(http.StatusNoContent)
+	}))
+	t.Cleanup(server.Close)
+	client := &fasthttp.Client{}
+	t.Cleanup(client.CloseIdleConnections)
+	manager := NewBackendHealthManager(client, "http://unused.invalid", server.URL+target, libpack_logger.New().SetOutput(io.Discard))
+	t.Cleanup(manager.Shutdown)
+	assert.True(t, manager.checkBackendHealth())
+}
+
+func TestBackendReadinessStatus(t *testing.T) {
+	for _, tc := range []struct {
+		name    string
+		status  int
+		healthy bool
+	}{
+		{name: "good OK", status: http.StatusOK, healthy: true},
+		{name: "good no content", status: http.StatusNoContent, healthy: true},
+		{name: "edge final success", status: 299, healthy: true},
+		{name: "bad redirect", status: http.StatusFound},
+		{name: "bad unauthorized", status: http.StatusUnauthorized},
+		{name: "bad unavailable", status: http.StatusServiceUnavailable},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				if r.URL.Path != "/ready" {
+					t.Error("readiness probe followed a redirect")
+					w.WriteHeader(http.StatusOK)
+					return
+				}
+				w.Header().Set("Location", "/redirected")
+				w.WriteHeader(tc.status)
+			}))
+			t.Cleanup(server.Close)
+			client := &fasthttp.Client{}
+			t.Cleanup(client.CloseIdleConnections)
+			manager := NewBackendHealthManager(client, server.URL, server.URL+"/ready", libpack_logger.New().SetOutput(io.Discard))
+			t.Cleanup(manager.Shutdown)
+			assert.Equal(t, tc.healthy, manager.checkBackendHealth())
+		})
+	}
+}
+
+func TestBackendReadinessNetworkFailure(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	}))
+	server.Close()
+	client := &fasthttp.Client{}
+	t.Cleanup(client.CloseIdleConnections)
+	manager := NewBackendHealthManager(client, server.URL, server.URL+"/ready", libpack_logger.New().SetOutput(io.Discard))
+	t.Cleanup(manager.Shutdown)
+	assert.False(t, manager.checkBackendHealth())
+}
+
+func TestBackendReadinessTimeout(t *testing.T) {
+	release := make(chan struct{})
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		<-release
+		w.WriteHeader(http.StatusOK)
+	}))
+	t.Cleanup(server.Close)
+	t.Cleanup(func() { close(release) })
+	client := &fasthttp.Client{ReadTimeout: 20 * time.Millisecond}
+	t.Cleanup(client.CloseIdleConnections)
+	manager := NewBackendHealthManager(client, server.URL, server.URL+"/ready", libpack_logger.New().SetOutput(io.Discard))
+	t.Cleanup(manager.Shutdown)
+	assert.False(t, manager.checkBackendHealth())
+}
+
+func TestBackendReadinessLegacyGraphQL(t *testing.T) {
+	for _, tc := range []struct {
+		name           string
+		configuredPath string
+		requestURI     string
+	}{
+		{name: "good bare host", requestURI: "/v1/graphql"},
+		{name: "edge root path", configuredPath: "/", requestURI: "/v1/graphql"},
+		{name: "good custom path and query", configuredPath: "/graphql?health=1", requestURI: "/graphql?health=1"},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				assert.Equal(t, http.MethodPost, r.Method)
+				assert.Equal(t, tc.requestURI, r.RequestURI)
+				assert.Equal(t, "application/json", r.Header.Get("Content-Type"))
+				assert.Empty(t, r.Header.Get("Authorization"))
+				body, err := io.ReadAll(r.Body)
+				assert.NoError(t, err)
+				assert.JSONEq(t, `{"query":"{__typename}"}`, string(body))
+				w.WriteHeader(http.StatusOK)
+			}))
+			t.Cleanup(server.Close)
+			client := &fasthttp.Client{}
+			t.Cleanup(client.CloseIdleConnections)
+			manager := NewBackendHealthManager(client, server.URL+tc.configuredPath, "", libpack_logger.New().SetOutput(io.Discard))
+			t.Cleanup(manager.Shutdown)
+			assert.True(t, manager.checkBackendHealth())
+		})
+	}
+}
+
+func readinessURLWithUserinfo(user *url.Userinfo) string {
+	u := url.URL{Scheme: "http", Host: "example.test", Path: "/ready", User: user}
+	return u.String()
+}
+
+func TestBackendReadinessURLValidation(t *testing.T) {
+	for _, tc := range []struct {
+		name  string
+		url   string
+		valid bool
+	}{
+		{name: "edge unset", valid: true},
+		{name: "good HTTP", url: "http://127.0.0.1:8080/ready", valid: true},
+		{name: "good HTTPS query", url: "https://example.test/check?database=primary", valid: true},
+		{name: "good IPv6", url: "http://[::1]:8080/ready", valid: true},
+		{name: "bad relative", url: "/ready"},
+		{name: "bad scheme", url: "ftp://example.test/ready"},
+		{name: "bad missing host", url: "http:///ready"},
+		{name: "bad port only host", url: "http://:8080/ready"},
+		{name: "bad opaque", url: "http:ready"},
+		{name: "bad userinfo", url: readinessURLWithUserinfo(url.UserPassword("operator", "secret"))},
+		{name: "bad user only", url: readinessURLWithUserinfo(url.User("operator"))},
+		{name: "bad escaped userinfo", url: strings.Replace(readinessURLWithUserinfo(url.UserPassword("operator", "%zz")), "%25zz", "%zz", 1)},
+		{name: "bad path escape", url: "http://example.test/%zz"},
+		{name: "bad port", url: "http://example.test:invalid/ready"},
+		{name: "bad port range", url: "http://example.test:65536/ready"},
+		{name: "bad fragment", url: "http://example.test/ready#ignored"},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			err := validateBackendHealthcheckURL(tc.url)
+			if tc.valid {
+				require.NoError(t, err)
+			} else {
+				require.Error(t, err)
+				assert.NotContains(t, err.Error(), tc.url)
+				assert.NotContains(t, err.Error(), "operator")
+				assert.NotContains(t, err.Error(), "secret")
+			}
+		})
+	}
+}
+
+func TestBackendReadinessInvalidConfigStopsStartup(t *testing.T) {
+	const helper = "GMP_TEST_INVALID_READINESS_CONFIG"
+	if os.Getenv(helper) == "1" {
+		parseConfig()
+		t.Fatal("invalid readiness configuration did not stop startup")
+	}
+	command := exec.Command(os.Args[0], "-test.run=^TestBackendReadinessInvalidConfigStopsStartup$")
+	for _, variable := range os.Environ() {
+		if !strings.HasPrefix(variable, "GMP_BACKEND_HEALTHCHECK_URL=") && !strings.HasPrefix(variable, helper+"=") {
+			command.Env = append(command.Env, variable)
+		}
+	}
+	command.Env = append(command.Env, helper+"=1", "GMP_BACKEND_HEALTHCHECK_URL="+readinessURLWithUserinfo(url.UserPassword("operator", "secret")))
+	output, err := command.CombinedOutput()
+	var exitError *exec.ExitError
+	require.ErrorAs(t, err, &exitError)
+	assert.Equal(t, 1, exitError.ExitCode())
+	assert.Contains(t, string(output), "Invalid BACKEND_HEALTHCHECK_URL")
+	assert.NotContains(t, string(output), "operator")
+	assert.NotContains(t, string(output), "secret")
+}

connection_resilience_test.go

@@ -77,16 +77,8 @@ func (suite *ConnectionResilienceTestSuite) TearDownTest() {
 
 // TestBackendHealthManager tests the backend health monitoring
 func (suite *ConnectionResilienceTestSuite) TestBackendHealthManager() {
-	suite.Run("initialization", func() {
-		healthMgr := NewBackendHealthManager(cfg.Client.FastProxyClient, cfg.Server.HostGraphQL, cfg.Logger)
-		suite.NotNil(healthMgr)
-		suite.Equal(cfg.Server.HostGraphQL, healthMgr.backendURL)
-		suite.Equal(5*time.Second, healthMgr.checkInterval)
-		suite.Equal(30, healthMgr.maxRetries)
-	})
-
 	suite.Run("health check success", func() {
-		healthMgr := NewBackendHealthManager(cfg.Client.FastProxyClient, cfg.Server.HostGraphQL, cfg.Logger)
+		healthMgr := NewBackendHealthManager(cfg.Client.FastProxyClient, cfg.Server.HostGraphQL, "", cfg.Logger)
 		isHealthy := healthMgr.checkBackendHealth()
 		suite.True(isHealthy)
 		suite.GreaterOrEqual(suite.mockServerCalled.Load(), int32(1))
@@ -94,13 +86,13 @@ func (suite *ConnectionResilienceTestSuite) TestBackendHealthManager() {
 
 	suite.Run("health check failure", func() {
 		// Use invalid URL to simulate failure
-		healthMgr := NewBackendHealthManager(cfg.Client.FastProxyClient, "http://invalid-url:99999", cfg.Logger)
+		healthMgr := NewBackendHealthManager(cfg.Client.FastProxyClient, "http://invalid-url:99999", "", cfg.Logger)
 		isHealthy := healthMgr.checkBackendHealth()
 		suite.False(isHealthy)
 	})
 
 	suite.Run("startup readiness with healthy backend", func() {
-		healthMgr := NewBackendHealthManager(cfg.Client.FastProxyClient, cfg.Server.HostGraphQL, cfg.Logger)
+		healthMgr := NewBackendHealthManager(cfg.Client.FastProxyClient, cfg.Server.HostGraphQL, "", cfg.Logger)
 		err := healthMgr.WaitForBackendReady(10 * time.Second)
 		suite.NoError(err)
 		suite.True(healthMgr.IsHealthy())
@@ -108,7 +100,7 @@ func (suite *ConnectionResilienceTestSuite) TestBackendHealthManager() {
 
 	suite.Run("startup readiness timeout", func() {
 		// Use invalid URL to simulate backend not ready
-		healthMgr := NewBackendHealthManager(cfg.Client.FastProxyClient, "http://invalid-url:99999", cfg.Logger)
+		healthMgr := NewBackendHealthManager(cfg.Client.FastProxyClient, "http://invalid-url:99999", "", cfg.Logger)
 		err := healthMgr.WaitForBackendReady(2 * time.Second)
 		suite.Error(err)
 		suite.Contains(err.Error(), "did not become ready")
@@ -177,7 +169,7 @@ func (suite *ConnectionResilienceTestSuite) TestConnectionPoolManager() {
 func (suite *ConnectionResilienceTestSuite) TestIntegratedHealthManagement() {
 	suite.Run("global initialization", func() {
 		// Initialize global instances
-		healthMgr := InitializeBackendHealth(cfg.Client.FastProxyClient, cfg.Server.HostGraphQL, cfg.Logger)
+		healthMgr := InitializeBackendHealth(cfg.Client.FastProxyClient, cfg.Server.HostGraphQL, "", cfg.Logger)
 		poolMgr := NewConnectionPoolManager(cfg.Client.FastProxyClient)
 
 		// Set global instances
@@ -194,7 +186,7 @@ func (suite *ConnectionResilienceTestSuite) TestIntegratedHealthManagement() {
 		// and may have already fired earlier in the process (e.g. via parseConfig in
 		// another test), in which case it returns whatever the global currently is —
 		// which TearDownTest above just nilled.
-		healthMgr := NewBackendHealthManager(cfg.Client.FastProxyClient, cfg.Server.HostGraphQL, cfg.Logger)
+		healthMgr := NewBackendHealthManager(cfg.Client.FastProxyClient, cfg.Server.HostGraphQL, "", cfg.Logger)
 		backendHealthManager = healthMgr
 
 		// Start health checking
@@ -272,7 +264,7 @@ func TestConnectionResilienceSuite(t *testing.T) {
 // periodic checking — otherwise the backend could never be marked healthy
 // again even after it recovers.
 func (suite *ConnectionResilienceTestSuite) TestHealthChecksStartAfterStartupTimeout() {
-	bhm := NewBackendHealthManager(cfg.Client.FastProxyClient, "http://invalid-url:99999", cfg.Logger)
+	bhm := NewBackendHealthManager(cfg.Client.FastProxyClient, "http://invalid-url:99999", "", cfg.Logger)
 	err := bhm.WaitForBackendReady(200 * time.Millisecond)
 	suite.Error(err, "expected timeout for unreachable backend")
 

coverage_micro_test.go

@@ -187,7 +187,7 @@ func TestCoverageMicro_BackendHealth(t *testing.T) {
 	client := &fasthttp.Client{}
 
 	t.Run("updateHealthStatus healthy→unhealthy transition", func(t *testing.T) {
-		bhm := NewBackendHealthManager(client, "http://localhost:9999", logger)
+		bhm := NewBackendHealthManager(client, "http://localhost:9999", "", logger)
 		defer bhm.Shutdown()
 
 		// Start healthy
@@ -203,7 +203,7 @@ func TestCoverageMicro_BackendHealth(t *testing.T) {
 	})
 
 	t.Run("updateHealthStatus unhealthy→healthy resets counter", func(t *testing.T) {
-		bhm := NewBackendHealthManager(client, "http://localhost:9999", logger)
+		bhm := NewBackendHealthManager(client, "http://localhost:9999", "", logger)
 		defer bhm.Shutdown()
 
 		bhm.isHealthy.Store(false)
@@ -219,7 +219,7 @@ func TestCoverageMicro_BackendHealth(t *testing.T) {
 	})
 
 	t.Run("GetLastHealthCheck round-trip", func(t *testing.T) {
-		bhm := NewBackendHealthManager(client, "http://localhost:9999", logger)
+		bhm := NewBackendHealthManager(client, "http://localhost:9999", "", logger)
 		defer bhm.Shutdown()
 
 		before := time.Now()

main.go

@@ -246,6 +246,33 @@ func validateJWTClaimPath(path string) error {
 	return nil
 }
 
+func validateBackendHealthcheckURL(rawURL string) error {
+	if rawURL == "" {
+		return nil
+	}
+	u, err := url.Parse(rawURL)
+	if err != nil {
+		// Parse errors can include credentials from the rejected URL.
+		return fmt.Errorf("must be a valid HTTP or HTTPS URL")
+	}
+	if (u.Scheme != "http" && u.Scheme != "https") || u.Hostname() == "" || u.Opaque != "" {
+		return fmt.Errorf("must use HTTP or HTTPS with a nonempty host")
+	}
+	if u.User != nil {
+		return fmt.Errorf("must not contain userinfo or credentials")
+	}
+	if u.Fragment != "" {
+		return fmt.Errorf("must not contain a fragment")
+	}
+	if port := u.Port(); port != "" {
+		n, err := strconv.Atoi(port)
+		if err != nil || n < 1 || n > 65535 {
+			return fmt.Errorf("must use a port between 1 and 65535")
+		}
+	}
+	return nil
+}
+
 // parseConfig loads and parses the configuration.
 func parseConfig() {
 	libpack_config.PKG_NAME = "graphql_proxy"
@@ -259,6 +286,11 @@ func parseConfig() {
 	c.Server.BindAddress = getDetailsFromEnv("BIND_ADDRESS", "")
 	c.Server.HostGraphQL = getDetailsFromEnv("HOST_GRAPHQL", "http://localhost/")
 	c.Server.HostGraphQLReadOnly = getDetailsFromEnv("HOST_GRAPHQL_READONLY", "")
+	c.Server.BackendHealthcheckURL = getDetailsFromEnv("BACKEND_HEALTHCHECK_URL", "")
+	if err := validateBackendHealthcheckURL(c.Server.BackendHealthcheckURL); err != nil {
+		fmt.Fprintf(os.Stderr, "CRITICAL ERROR: Invalid BACKEND_HEALTHCHECK_URL: %v\n", err)
+		os.Exit(1)
+	}
 	// Client configurations
 	c.Client.JWTUserClaimPath = getDetailsFromEnv("JWT_USER_CLAIM_PATH", "")
 	c.Client.JWTRoleClaimPath = getDetailsFromEnv("JWT_ROLE_CLAIM_PATH", "")
@@ -678,7 +710,7 @@ func parseConfig() {
 
 	// Initialize backend health manager
 	if cfg.Server.HostGraphQL != "" {
-		healthMgr := InitializeBackendHealth(cfg.Client.FastProxyClient, cfg.Server.HostGraphQL, cfg.Logger)
+		healthMgr := InitializeBackendHealth(cfg.Client.FastProxyClient, cfg.Server.HostGraphQL, cfg.Server.BackendHealthcheckURL, cfg.Logger)
 		// Start health checking in background
 		healthMgr.StartHealthChecking()
 	}

struct_config.go

@@ -67,6 +67,7 @@ type config struct {
 		HostGraphQL           string
 		HostGraphQLReadOnly   string
 		HealthcheckGraphQL    string
+		BackendHealthcheckURL string
 		AllowURLs             []string // List of allowed URL paths for access control
 		// BindAddress is the host portion of every listener's bind address
 		// (GraphQL proxy, admin API, monitoring). Empty (the default)