Make missing cache-address validation error generic across cache types

CHANGELOG.md

@@ -77,6 +77,7 @@
 * [BUGFIX] Querier: Fix panic due to request tracker truncating multi-byte UTF-8 character #7640
 * [BUGFIX] Ingester: Fix panic (`HistogramProtoToHistogram called with a float histogram`) when ingesting a float native histogram with a zero count (e.g. a staleness marker or empty histogram). The decoder is now selected by histogram type via `IsFloatHistogram()` instead of by count value. #7645
 * [BUGFIX] Querier: Fix parquet queryable fallback returning a nil error instead of the actual query error in `LabelValues` and `LabelNames`. #7638
+* [BUGFIX] Store Gateway: Fix misleading "no index cache backend addresses" validation error being reported for chunks-cache, metadata-cache, and parquet caches when their memcached or redis backend is configured without addresses. The message is now the cache-type-agnostic "no cache backend addresses". #PENDING
 
 ## 1.21.0 2026-04-24
 

pkg/storage/tsdb/caching_bucket_test.go

@@ -75,6 +75,18 @@ func Test_BucketCacheBackendValidation(t *testing.T) {
 			},
 			expectedErr: errUnsupportedBucketCacheBackend,
 		},
+		"memcached backend without addresses": {
+			cfg: BucketCacheBackend{
+				Backend: CacheBackendMemcached,
+			},
+			expectedErr: errNoIndexCacheAddresses,
+		},
+		"redis backend without addresses": {
+			cfg: BucketCacheBackend{
+				Backend: CacheBackendRedis,
+			},
+			expectedErr: errNoIndexCacheAddresses,
+		},
 		"valid multi bucket cache type": {
 			cfg: BucketCacheBackend{
 				Backend: fmt.Sprintf("%s,%s,%s", CacheBackendInMemory, CacheBackendMemcached, CacheBackendRedis),
@@ -155,6 +167,20 @@ func Test_BucketCacheBackendValidation(t *testing.T) {
 	}
 }
 
+func Test_BucketCacheBackendValidation_MissingAddressesErrorIsGeneric(t *testing.T) {
+	// A bucket cache (e.g. chunks-cache) is not an index cache, so the missing
+	// addresses error must not mention "index cache". See issue #6804.
+	for _, cfg := range []BucketCacheBackend{
+		{Backend: CacheBackendMemcached},
+		{Backend: CacheBackendRedis},
+	} {
+		err := cfg.Validate()
+		require.Error(t, err)
+		assert.Equal(t, "no cache backend addresses", err.Error())
+		assert.NotContains(t, err.Error(), "index cache")
+	}
+}
+
 func Test_BucketIndexCache(t *testing.T) {
 	const bucketIndexFile = "user1/bucket-index.json.gz"
 	const fileContent = "test-content"

pkg/storage/tsdb/index_cache.go

@@ -41,7 +41,7 @@ var (
 
 	errUnsupportedIndexCacheBackend = errors.New("unsupported index cache backend")
 	errDuplicatedIndexCacheBackend  = errors.New("duplicated index cache backend")
-	errNoIndexCacheAddresses        = errors.New("no index cache backend addresses")
+	errNoIndexCacheAddresses        = errors.New("no cache backend addresses")
 	errInvalidMaxAsyncConcurrency   = errors.New("invalid max_async_concurrency, must greater than 0")
 	errInvalidMaxAsyncBufferSize    = errors.New("invalid max_async_buffer_size, must greater than 0")
 	errInvalidMaxBackfillItems      = errors.New("invalid max_backfill_items, must greater than 0")