Add per-checker remote address CLI flags

Register one -checker-<id>-remote-address flag per registered checker,
allowing operators to delegate a checker's observation collection to a
remote HTTP service at startup. When set, the CLI/config value wins
over any per-checker "endpoint" AdminOpt.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/app/app.go

@@ -287,6 +287,11 @@ func (app *App) initUsecases() {
 		app.store,
 		app.store,
 	)
+	if setter, ok := app.usecases.checkerEngine.(interface {
+		SetRemoteAddresses(map[string]string)
+	}); ok {
+		setter.SetRemoteAddresses(app.cfg.CheckerRemoteAddresses)
+	}
 	// Build the user-level gate so paused or long-inactive users do not
 	// get checked. The same user resolver is reused by the janitor for
 	// per-user retention overrides.

internal/config/cli.go

@@ -27,6 +27,7 @@ import (
 	"runtime"
 	"time"
 
+	"git.happydns.org/happyDomain/internal/checker"
 	"git.happydns.org/happyDomain/internal/storage"
 	"git.happydns.org/happyDomain/model"
 )
@@ -70,6 +71,20 @@ func declareFlags(o *happydns.Options) {
 
 	flag.Var(&stringSlice{&o.PluginsDirectories}, "plugins-directory", "Path to a directory containing checker plugins (.so files); may be repeated")
 
+	// One -checker-<id>-remote-address flag per registered checker. Checkers
+	// register themselves in init() of the blank-imported `checkers` package,
+	// so by the time declareFlags runs the registry is fully populated.
+	if o.CheckerRemoteAddresses == nil {
+		o.CheckerRemoteAddresses = map[string]string{}
+	}
+	for id := range checker.GetCheckers() {
+		flag.Var(
+			&mapEntry{Map: &o.CheckerRemoteAddresses, Key: id},
+			fmt.Sprintf("checker-%s-remote-address", id),
+			fmt.Sprintf("URL of a remote HTTP service that should run the %q checker (overrides any per-checker endpoint AdminOpt)", id),
+		)
+	}
+
 	// Others flags are declared in some other files likes sources, storages, ... when they need specials configurations
 }
 

internal/config/custom.go

@@ -46,6 +46,29 @@ func (s *stringSlice) Set(value string) error {
 	return nil
 }
 
+// mapEntry is a flag.Value that writes the flag value into a map under a
+// preset key. Used to register one flag per checker writing into a shared
+// map[string]string on Options.
+type mapEntry struct {
+	Map *map[string]string
+	Key string
+}
+
+func (m *mapEntry) String() string {
+	if m.Map == nil || *m.Map == nil {
+		return ""
+	}
+	return (*m.Map)[m.Key]
+}
+
+func (m *mapEntry) Set(value string) error {
+	if *m.Map == nil {
+		*m.Map = map[string]string{}
+	}
+	(*m.Map)[m.Key] = value
+	return nil
+}
+
 type JWTSecretKey struct {
 	Secret *[]byte
 }

internal/usecase/checker/checker_engine.go

@@ -34,14 +34,23 @@ import (
 
 // checkerEngine implements the happydns.CheckerEngine interface.
 type checkerEngine struct {
-	optionsUC     *CheckerOptionsUsecase
-	evalStore     CheckEvaluationStorage
-	execStore     ExecutionStorage
-	snapStore     ObservationSnapshotStorage
-	cacheStore    ObservationCacheStorage
-	entryStore    DiscoveryEntryStorage
-	obsRefStore   DiscoveryObservationStorage
-	relatedLookup checkerPkg.RelatedObservationLookup
+	optionsUC       *CheckerOptionsUsecase
+	evalStore       CheckEvaluationStorage
+	execStore       ExecutionStorage
+	snapStore       ObservationSnapshotStorage
+	cacheStore      ObservationCacheStorage
+	entryStore      DiscoveryEntryStorage
+	obsRefStore     DiscoveryObservationStorage
+	relatedLookup   checkerPkg.RelatedObservationLookup
+	remoteAddresses map[string]string
+}
+
+// SetRemoteAddresses installs a checker-ID -> remote HTTP endpoint map. When
+// a non-empty entry exists for a checker, runPipeline routes its observation
+// collection through the remote service instead of the local provider, and
+// takes precedence over any per-checker "endpoint" AdminOpt.
+func (e *checkerEngine) SetRemoteAddresses(addrs map[string]string) {
+	e.remoteAddresses = addrs
 }
 
 // NewCheckerEngine creates a new CheckerEngine implementation. Passing nil
@@ -189,8 +198,14 @@ func (e *checkerEngine) runPipeline(ctx context.Context, def *happydns.CheckerDe
 		obsCtx.SetRelatedLookup(def.ID, e.relatedLookup)
 	}
 
-	// If an endpoint is configured, override observation providers with HTTP transport.
-	if endpoint, ok := mergedOpts["endpoint"].(string); ok && endpoint != "" {
+	// If an endpoint is configured, override observation providers with HTTP
+	// transport. The CLI/config -checker-<id>-remote-address value (if set)
+	// wins over the per-checker "endpoint" AdminOpt.
+	endpoint, _ := mergedOpts["endpoint"].(string)
+	if cli, ok := e.remoteAddresses[def.ID]; ok && cli != "" {
+		endpoint = cli
+	}
+	if endpoint != "" {
 		for _, key := range def.ObservationKeys {
 			obsCtx.SetProviderOverride(key, checkerPkg.NewHTTPObservationProvider(key, endpoint))
 		}

model/config.go

@@ -134,6 +134,12 @@ type Options struct {
 	// PluginsDirectories lists filesystem paths scanned at startup for
 	// checker plugins (.so files).
 	PluginsDirectories []string
+
+	// CheckerRemoteAddresses maps a checker ID to the URL of a remote HTTP
+	// service that should run that checker's observation collection. When
+	// set for a given checker, this CLI/config value takes precedence over
+	// any per-checker "endpoint" AdminOpt.
+	CheckerRemoteAddresses map[string]string
 }
 
 // GetBaseURL returns the full url to the absolute ExternalURL, including BaseURL.