Add `-list-targets` command line flag (#4920)

* Add -list-targets flag to list available targets

Signed-off-by: Christian Haudum <christian.haudum@gmail.com>

* Mark user-invisible modules as such

so they are not shown as run targets when listing available targets
using the `-list-targets` flag.

Signed-off-by: Christian Haudum <christian.haudum@gmail.com>

* Mention command line flag in configuration docs

Signed-off-by: Christian Haudum <christian.haudum@gmail.com>

* Add changelog entry

Signed-off-by: Christian Haudum <christian.haudum@gmail.com>

* fixup! Add -list-targets flag to list available targets

Signed-off-by: Christian Haudum <christian.haudum@gmail.com>

CHANGELOG.md

@@ -1,5 +1,6 @@
 ## Main
 
+* [4920](https://github.com/grafana/loki/pull/4920) **chaudum**: Add `-list-targets` command line flag to list all available run targets
 * [4860](https://github.com/grafana/loki/pull/4860) **cyriltovena**: Add rate limiting and metrics to hedging
 * [4865](https://github.com/grafana/loki/pull/4865) **taisho6339**: Fix duplicate registry.MustRegister call in Promtail Kafka
 * [4845](https://github.com/grafana/loki/pull/4845) **chaudum** Return error responses consistently as JSON

cmd/loki/main.go

@@ -91,6 +91,11 @@ func main() {
 	t, err := loki.New(config.Config)
 	util_log.CheckFatal("initialising loki", err)
 
+	if config.ListTargets {
+		t.ListTargets()
+		os.Exit(0)
+	}
+
 	level.Info(util_log.Logger).Log("msg", "Starting Loki", "version", version.Info())
 
 	err = t.Run(loki.RunOpts{})

docs/sources/configuration/_index.md

@@ -86,6 +86,7 @@ Pass the `-config.expand-env` flag at the command line to enable this way of set
 # the distributor and compactor, but all in the same process.
 # Supported values: all, compactor, distributor, ingester, querier, query-scheduler,
 #  ingester-querier, query-frontend, index-gateway, ruler, table-manager, read, write.
+# A full list of available targets can be printed when running Loki with the `-list-targets` command line flag.
 [target: <string> | default = "all"]
 
 # Enables authentication through the X-Scope-OrgID header, which must be present

pkg/loki/config_wrapper.go

@@ -31,6 +31,7 @@ type ConfigWrapper struct {
 	PrintVersion    bool
 	VerifyConfig    bool
 	PrintConfig     bool
+	ListTargets     bool
 	LogConfig       bool
 	ConfigFile      string
 	ConfigExpandEnv bool
@@ -40,6 +41,7 @@ func (c *ConfigWrapper) RegisterFlags(f *flag.FlagSet) {
 	f.BoolVar(&c.PrintVersion, "version", false, "Print this builds version information")
 	f.BoolVar(&c.VerifyConfig, "verify-config", false, "Verify config file and exits")
 	f.BoolVar(&c.PrintConfig, "print-config-stderr", false, "Dump the entire Loki config object to stderr")
+	f.BoolVar(&c.ListTargets, "list-targets", false, "List available targets")
 	f.BoolVar(&c.LogConfig, "log-config-reverse-order", false, "Dump the entire Loki config object at Info log "+
 		"level with the order reversed, reversing the order makes viewing the entries easier in Grafana.")
 	f.StringVar(&c.ConfigFile, "config.file", "", "yaml file to load")

pkg/loki/loki.go

@@ -6,6 +6,8 @@ import (
 	"flag"
 	"fmt"
 	"net/http"
+	"os"
+	rt "runtime"
 
 	cortex_tripper "github.com/cortexproject/cortex/pkg/querier/queryrange"
 	cortex_ruler "github.com/cortexproject/cortex/pkg/ruler"
@@ -13,6 +15,7 @@ import (
 	"github.com/cortexproject/cortex/pkg/util"
 	"github.com/cortexproject/cortex/pkg/util/fakeauth"
 	util_log "github.com/cortexproject/cortex/pkg/util/log"
+	"github.com/fatih/color"
 	"github.com/felixge/fgprof"
 	"github.com/go-kit/log/level"
 	"github.com/grafana/dskit/flagext"
@@ -295,6 +298,24 @@ func (t *Loki) bindConfigEndpoint(opts RunOpts) {
 	t.Server.HTTP.Path("/config").Methods("GET").HandlerFunc(configEndpointHandlerFn)
 }
 
+// ListTargets prints a list of available user visible targets and their
+// dependencies
+func (t *Loki) ListTargets() {
+	green := color.New(color.FgGreen, color.Bold)
+	if rt.GOOS == "windows" {
+		green.DisableColor()
+	}
+	for _, m := range t.ModuleManager.UserVisibleModuleNames() {
+		fmt.Fprintln(os.Stdout, green.Sprint(m))
+
+		for _, n := range t.ModuleManager.DependenciesForModule(m) {
+			if t.ModuleManager.IsUserVisibleModule(n) {
+				fmt.Fprintln(os.Stdout, " ", n)
+			}
+		}
+	}
+}
+
 // Run starts Loki running, and blocks until a Loki stops.
 func (t *Loki) Run(opts RunOpts) error {
 	serviceMap, err := t.ModuleManager.InitModuleServices(t.Cfg.Target...)
@@ -427,15 +448,15 @@ func (t *Loki) readyHandler(sm *services.Manager) http.HandlerFunc {
 func (t *Loki) setupModuleManager() error {
 	mm := modules.NewManager(util_log.Logger)
 
-	mm.RegisterModule(Server, t.initServer)
-	mm.RegisterModule(RuntimeConfig, t.initRuntimeConfig)
-	mm.RegisterModule(MemberlistKV, t.initMemberlistKV)
-	mm.RegisterModule(Ring, t.initRing)
-	mm.RegisterModule(Overrides, t.initOverrides)
+	mm.RegisterModule(Server, t.initServer, modules.UserInvisibleModule)
+	mm.RegisterModule(RuntimeConfig, t.initRuntimeConfig, modules.UserInvisibleModule)
+	mm.RegisterModule(MemberlistKV, t.initMemberlistKV, modules.UserInvisibleModule)
+	mm.RegisterModule(Ring, t.initRing, modules.UserInvisibleModule)
+	mm.RegisterModule(Overrides, t.initOverrides, modules.UserInvisibleModule)
 	mm.RegisterModule(OverridesExporter, t.initOverridesExporter)
-	mm.RegisterModule(TenantConfigs, t.initTenantConfigs)
+	mm.RegisterModule(TenantConfigs, t.initTenantConfigs, modules.UserInvisibleModule)
 	mm.RegisterModule(Distributor, t.initDistributor)
-	mm.RegisterModule(Store, t.initStore)
+	mm.RegisterModule(Store, t.initStore, modules.UserInvisibleModule)
 	mm.RegisterModule(Ingester, t.initIngester)
 	mm.RegisterModule(Querier, t.initQuerier)
 	mm.RegisterModule(IngesterQuerier, t.initIngesterQuerier)