Add warnings for suspect configurations

CHANGELOG.md

@@ -1,4 +1,5 @@
 ## master / unreleased
 
 * [CHANGE] Bloom filters are now sharded to reduce size and improve caching, as blocks grow. This is a **breaking change** and all data stored before this change will **not** be queryable. [192](https://github.com/grafana/tempo/pull/192)
-* [ENHANCEMENT] CI checks for vendored dependencies using `make vendor-check`. Update CONTRIBUTING.md to reflect the same before checking in files in a PR. [#274](https://github.com/grafana/tempo/pull/274)
+* [ENHANCEMENT] CI checks for vendored dependencies using `make vendor-check`. Update CONTRIBUTING.md to reflect the same before checking in files in a PR. [#274](https://github.com/grafana/tempo/pull/274)
+* [ENHANCEMENT] Add warnings for suspect configs. [#294](https://github.com/grafana/tempo/pull/294)

cmd/tempo/app/app.go

@@ -83,6 +83,19 @@ func (c *Config) RegisterFlagsAndApplyDefaults(prefix string, f *flag.FlagSet) {
 
 }
 
+// CheckConfig checks if config values are suspect.
+func (c *Config) CheckConfig() {
+	if c.Ingester.CompleteBlockTimeout < c.StorageConfig.Trace.MaintenanceCycle {
+		level.Warn(util.Logger).Log("msg", "3ingester.CompleteBlockTimeout < storage.trace.maintenance-cycle",
+			"explan", "You may receive 404s between the time the ingesters have flushed a trace and the querier is aware of the new block")
+	}
+
+	if c.Compactor.Compactor.BlockRetention < c.StorageConfig.Trace.MaintenanceCycle {
+		level.Warn(util.Logger).Log("msg", "compactor.CompactedBlockRetention < storage.trace.maintenance-cycle",
+			"explan", "Queriers and Compactors may attempt to read a block that no longer exists")
+	}
+}
+
 // App is the root datastructure.
 type App struct {
 	cfg Config

cmd/tempo/main.go

@@ -76,6 +76,9 @@ func main() {
 	// Allocate a block of memory to alter GC behaviour. See https://github.com/golang/go/issues/23044
 	ballast := make([]byte, *ballastMBs*1024*1024)
 
+	// Warn the user for suspect configurations
+	config.CheckConfig()
+
 	// Start Tempo
 	t, err := app.New(*config)
 	if err != nil {