thanos-io/thanos · error

failed to create groupcache

Error message

failed to create groupcache

What it means

When the cache type is GROUPCACHE, the factory initializes a groupcache instance via cache.NewGroupcache using a base HTTP path (/_galaxycache/); failures are wrapped as 'failed to create groupcache'. Groupcache ties into the provided HTTP router and bucket, so registration problems surface here.

Solutions

1. Check the wrapped inner error for the exact registration/config failure
2. Ensure no other handler is registered on the groupcache base path /_galaxycache/
3. Validate groupcache options (peers, max group bytes) in the backend config
4. Confirm your Thanos version supports the GROUPCACHE provider for this component
5. Switch to MEMCACHED or REDIS if groupcache is not supported in your deployment

Example fix

// before
cacheConfig:
  type: GROUPCACHE
  groupcache:
    maxsize: "abc"   # unparseable size
// after
cacheConfig:
  type: GROUPCACHE
  groupcache:
    maxsize: 1GB

if router == nil || bucket == nil { return errors.New("groupcache requires a non-nil router and bucket") }
if h := router.Get("/_galaxycache/"); h != nil { return errors.New("path /_galaxycache/ already registered") }

cb, err := storecache.NewCachingBucketFromYaml(yamlContent, logger, reg, bucket, router)
if err != nil {
    if strings.Contains(err.Error(), "failed to create groupcache") {
        return fmt.Errorf("groupcache init failed (check path conflict and groupcache config): %w", err)
    }
    return err
}

When it happens

Trigger: CachingWithBackendConfig.Type == GROUPCACHE and NewGroupcache returns an error — commonly invalid groupcache config in backendConfig, conflicts registering the /_galaxycache/ path on the provided route.Router, or a nil bucket/router dependency.

Common situations: Running a component where the passed router already serves the same path, groupcache options mis-sized (max bytes per group), or attempting groupcache in a Thanos build/component that does not support it.

Related errors

• failed to parse template
• failed to execute template
• failed to parse the template
• failed to execute the template
• scrape manager not ready

AI-assisted analysis of thanos-io/thanos@35b8b99117 (2026-09-07). Data as JSON: /api/errors/d0307183add35446. Report an issue: GitHub.

Appendix: source

Thrown at pkg/store/cache/caching_bucket_factory.go:128

	switch strings.ToUpper(string(config.Type)) {
	case string(MemcachedBucketCacheProvider):
		var memcached cacheutil.RemoteCacheClient
		memcached, err := cacheutil.NewMemcachedClient(logger, "caching-bucket", backendConfig, reg)
		if err != nil {
			return nil, errors.Wrapf(err, "failed to create memcached client")
		}
		c = cache.NewMemcachedCache("caching-bucket", logger, memcached, reg)
	case string(InMemoryBucketCacheProvider):
		c, err = cache.NewInMemoryCache("caching-bucket", logger, reg, backendConfig)
		if err != nil {
			return nil, errors.Wrapf(err, "failed to create inmemory cache")
		}
	case string(GroupcacheBucketCacheProvider):
		const basePath = "/_galaxycache/"

		c, err = cache.NewGroupcache(logger, reg, backendConfig, basePath, r, bucket, cfg)
		if err != nil {
			return nil, errors.Wrap(err, "failed to create groupcache")
		}

	case string(RedisBucketCacheProvider):
		redisCache, err := cacheutil.NewRedisClient(logger, "caching-bucket", backendConfig, reg)
		if err != nil {
			return nil, errors.Wrapf(err, "failed to create redis client")
		}
		c = cache.NewRedisCache("caching-bucket", logger, redisCache, reg)
	default:
		return nil, errors.Errorf("unsupported cache type: %s", config.Type)
	}

	// Include interactions with cache in the traces.
	c = cache.NewTracingCache(c)
	cfg.SetCacheImplementation(c)

	cb, err := NewCachingBucket(bucket, cfg, logger, reg)
	if err != nil {

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