Unistore: Reuse MySQL and Postgres Grafana core config instead of the object (#94223)

* Reuse MySQL and Postgres Grafana config instead of the object

- Only reuse the Grafana DB object for SQLite. Support for SQLite will be added in a different PR
- Fail when reusing the Grafana DB object if it is using DB instrumentation
- In the case that we have to reuse a Grafana DB with its instrumentation, fail with an error that describes a workaround
- Add regression tests to reproduce incident 2144

* remove temp file

* fix linter

* fix linter x2

* fix linter x3

pkg/storage/unified/sql/db/dbimpl/dbimpl.go

@@ -2,6 +2,7 @@ package dbimpl
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"sync"
 
@@ -12,7 +13,6 @@ import (
 
 	infraDB "github.com/grafana/grafana/pkg/infra/db"
 	"github.com/grafana/grafana/pkg/infra/log"
-	"github.com/grafana/grafana/pkg/services/featuremgmt"
 	"github.com/grafana/grafana/pkg/setting"
 	"github.com/grafana/grafana/pkg/storage/unified/sql/db"
 	"github.com/grafana/grafana/pkg/storage/unified/sql/db/migrations"
@@ -23,8 +23,17 @@ const (
 	dbTypePostgres = "postgres"
 )
 
-func ProvideResourceDB(grafanaDB infraDB.DB, cfg *setting.Cfg, features featuremgmt.FeatureToggles, tracer tracing.Tracer) (db.DBProvider, error) {
-	p, err := newResourceDBProvider(grafanaDB, cfg, features, tracer)
+const grafanaDBInstrumentQueriesKey = "instrument_queries"
+
+var errGrafanaDBInstrumentedNotSupported = errors.New("the Resource API is " +
+	"attempting to leverage the database from core Grafana defined in the" +
+	" [database] INI section since a database configuration was not provided" +
+	" in the [resource_api] section. But we detected that the key `" +
+	grafanaDBInstrumentQueriesKey + "` is enabled in [database], and that" +
+	" setup is currently unsupported. Please, consider disabling that flag")
+
+func ProvideResourceDB(grafanaDB infraDB.DB, cfg *setting.Cfg, tracer tracing.Tracer) (db.DBProvider, error) {
+	p, err := newResourceDBProvider(grafanaDB, cfg, tracer)
 	if err != nil {
 		return nil, fmt.Errorf("provide Resource DB: %w", err)
 	}
@@ -54,41 +63,67 @@ type resourceDBProvider struct {
 	logQueries      bool
 }
 
-func newResourceDBProvider(grafanaDB infraDB.DB, cfg *setting.Cfg, features featuremgmt.FeatureToggles, tracer tracing.Tracer) (p *resourceDBProvider, err error) {
-	// TODO: This should be renamed resource_api
-	getter := &sectionGetter{
-		DynamicSection: cfg.SectionWithEnvOverrides("resource_api"),
-	}
+func newResourceDBProvider(grafanaDB infraDB.DB, cfg *setting.Cfg, tracer tracing.Tracer) (p *resourceDBProvider, err error) {
+	// Resource API has other configs in its section besides database ones, so
+	// we prefix them with "db_". We use the database config from core Grafana
+	// as fallback, and as it uses a dedicated INI section, then keys are not
+	// prefixed with "db_"
+	getter := newConfGetter(cfg.SectionWithEnvOverrides("resource_api"), "db_")
+	fallbackGetter := newConfGetter(cfg.SectionWithEnvOverrides("database"), "")
 
 	p = &resourceDBProvider{
 		cfg:         cfg,
 		log:         log.New("entity-db"),
-		logQueries:  getter.Key("log_queries").MustBool(false),
+		logQueries:  getter.Bool("log_queries"),
 		migrateFunc: migrations.MigrateResourceStore,
 	}
 
-	switch dbType := getter.Key("db_type").MustString(""); dbType {
-	case dbTypePostgres:
+	dbType := getter.String("type")
+	grafanaDBType := fallbackGetter.String("type")
+	switch {
+	// First try with the config in the "resource_api" section, which is
+	// specific to Unified Storage
+	case dbType == dbTypePostgres:
 		p.registerMetrics = true
 		p.engine, err = getEnginePostgres(getter, tracer)
 		return p, err
 
-	case dbTypeMySQL:
+	case dbType == dbTypeMySQL:
 		p.registerMetrics = true
 		p.engine, err = getEngineMySQL(getter, tracer)
 		return p, err
 
-	case "":
+		// TODO: add support for SQLite
+
+	case dbType != "":
+		return p, fmt.Errorf("invalid db type specified: %s", dbType)
+
+	// If we have an empty Resource API db config, try with the core Grafana
+	// database config
+
+	case grafanaDBType == dbTypePostgres:
+		p.registerMetrics = true
+		p.engine, err = getEnginePostgres(fallbackGetter, tracer)
+		return p, err
+
+	case grafanaDBType == dbTypeMySQL:
+		p.registerMetrics = true
+		p.engine, err = getEngineMySQL(fallbackGetter, tracer)
+		return p, err
+
+	// TODO: add support for SQLite
+
+	case grafanaDB != nil:
 		// try to use the grafana db connection
-		if grafanaDB == nil {
-			return p, fmt.Errorf("no db connection provided")
+
+		if fallbackGetter.Bool(grafanaDBInstrumentQueriesKey) {
+			return nil, errGrafanaDBInstrumentedNotSupported
 		}
 		p.engine = grafanaDB.GetEngine()
 		return p, nil
 
 	default:
-		// TODO: sqlite support
-		return p, fmt.Errorf("invalid db type specified: %s", dbType)
+		return p, fmt.Errorf("no db connection provided")
 	}
 }
 
@@ -102,7 +137,6 @@ func (p *resourceDBProvider) init(ctx context.Context) (db.DB, error) {
 	_ = p.logQueries // TODO: configure SQL logging
 
 	// TODO: change the migrator to use db.DB instead of xorm
-	// Skip migrations if feature flag is not enabled
 	if p.migrateFunc != nil {
 		err := p.migrateFunc(ctx, p.engine, p.cfg)
 		if err != nil {