Fix sanity check done on configured filesystem directories when running Alertmanager in microservices mode (#2947) (#2948)

* Fix sanity check done on configured filesystem directories when running Alertmanager in microservices mode

Signed-off-by: Marco Pracucci <marco@pracucci.com>

* Added CHANGELOG entry

Signed-off-by: Marco Pracucci <marco@pracucci.com>

Signed-off-by: Marco Pracucci <marco@pracucci.com>
(cherry picked from commit bfad6ac)

Author: pracucci

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 ### Grafana Mimir
 
+* [BUGFIX] Fix sanity check done on configured filesystem directories when running Alertmanager in microservices mode. #2947
+
 ### Mixin
 
 ### Jsonnet

pkg/mimir/mimir.go

@@ -325,7 +325,8 @@ func (c *Config) validateFilesystemPaths(logger log.Logger) error {
 
 	var paths []pathConfig
 
-	if c.BlocksStorage.Bucket.Backend == bucket.Filesystem {
+	// Blocks storage (check only for components using it).
+	if c.isAnyModuleEnabled(All, Write, Read, Backend, Ingester, Querier, StoreGateway, Compactor, Ruler) && c.BlocksStorage.Bucket.Backend == bucket.Filesystem {
 		// Add the optional prefix to the path, because that's the actual location where blocks will be stored.
 		paths = append(paths, pathConfig{
 			name:       "blocks storage filesystem directory",

pkg/mimir/mimir_test.go

@@ -542,6 +542,25 @@ func TestConfig_validateFilesystemPaths(t *testing.T) {
 				cfg.BlocksStorage.Bucket.Filesystem.Directory = "./data-blocks"
 			},
 		},
+		"should succeed if blocks storage filesystem directory overlaps with alertmanager data directory, but we're running alertmanager in microservices mode": {
+			setup: func(cfg *Config) {
+				cfg.Target = flagext.StringSliceCSV{AlertManager}
+				cfg.BlocksStorage.Bucket.Backend = bucket.Filesystem
+				cfg.BlocksStorage.Bucket.Filesystem.Directory = "blocks"
+				cfg.AlertmanagerStorage.Backend = bucket.Filesystem
+				cfg.AlertmanagerStorage.Filesystem.Directory = "/data/alertmanager"
+				cfg.Alertmanager.DataDir = cwd
+			},
+		},
+		"should fail if blocks storage filesystem directory overlaps with alertmanager data directory, and alertmanager is running along with other components": {
+			setup: func(cfg *Config) {
+				cfg.Target = flagext.StringSliceCSV{All, AlertManager}
+				cfg.Common.Storage.Backend = bucket.Filesystem
+				cfg.Common.Storage.Filesystem.Directory = "blocks"
+				cfg.Alertmanager.DataDir = cwd
+			},
+			expectedErr: fmt.Sprintf(`the configured blocks storage filesystem directory "blocks" cannot overlap with the configured alertmanager data directory "%s"`, cwd),
+		},
 	}
 
 	for testName, testData := range tests {