thanos-io/thanos · error

failed to create memcached client

Error message

failed to create memcached client

What it means

When the configured cache type is MEMCACHED, the factory creates a memcached client via cacheutil.NewMemcachedClient; failure is wrapped as 'failed to create memcached client'. This occurs before any network call — the client constructor itself rejects its configuration (addresses, timeouts, DNS setup).

Solutions

1. Verify the addresses field lists reachable memcached hosts (correct service DNS name and port 11211)
2. Check timeout/duration fields parse as Go durations (e.g. 500ms, 1s)
3. Ensure the memcached Service/Endpoints exist and DNS resolves (kubectl get endpoints)
4. Validate max_idle_connections and other client options are positive values
5. Log the wrapped inner error — it names the exact invalid parameter

Example fix

// before
addresses: memcached.invalid-namespace.svc:11211
// after
addresses: memcached.monitoring.svc.cluster.local:11211
dns_provider_update_interval: 10s

for _, a := range strings.Fields(memcachedAddresses) {
    if _, _, err := net.SplitHostPort(a); err != nil { return fmt.Errorf("bad memcached address %q: %w", a, err) }
}

cb, err := storecache.NewCachingBucketFromYaml(yamlContent, logger, reg, bucket, router)
if err != nil {
    var se *status.Error
    if strings.Contains(err.Error(), "failed to create memcached client") {
        return fmt.Errorf("memcached addresses/timeout invalid; check DNS and durations: %w", err)
    }
    return err
}

When it happens

Trigger: CachingWithBackendConfig.Type == MEMCACHED and NewMemcachedClient returns an error, e.g. empty/invalid host list, unparseable addresses, invalid timeout/duration values, or failure resolving service DNS (SRV) addresses at construction.

Common situations: Kubernetes users pointing at a wrong memcached Service name or port, misconfigured addresses string (space-separated list), or invalid memcached_client_timeout values in the YAML.

Related errors

• failed to parse template
• failed to execute template
• error while parsing config for request logging
• getting http client config
• parsing http config YAML

AI-assisted analysis of thanos-io/thanos@35b8b99117 (2026-09-07). Data as JSON: /api/errors/f327ac333221a2a7. Report an issue: GitHub.

Appendix: source

Thrown at pkg/store/cache/caching_bucket_factory.go:115

	var c cache.Cache
	cfg := cache.NewCachingBucketConfig()

	// Configure cache paths.
	cfg.CacheAttributes("chunks", nil, isTSDBChunkFile, config.ChunkObjectAttrsTTL)
	cfg.CacheGetRange("chunks", nil, isTSDBChunkFile, config.ChunkSubrangeSize, config.ChunkObjectAttrsTTL, config.ChunkSubrangeTTL, config.MaxChunksGetRangeRequests)
	cfg.CacheExists("meta.jsons", nil, isMetaFile, config.MetafileExistsTTL, config.MetafileDoesntExistTTL)
	cfg.CacheGet("meta.jsons", nil, isMetaFile, int(config.MetafileMaxSize), config.MetafileContentTTL, config.MetafileExistsTTL, config.MetafileDoesntExistTTL)

	// Cache Iter requests for root.
	cfg.CacheIter("blocks-iter", nil, isBlocksRootDir, config.BlocksIterTTL, JSONIterCodec{}, cfgHash)

	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 {

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