cannot create a %s reader with an empty list of broker addre

Error message

cannot create a %s reader with an empty list of broker addresses

What it means

After parsing the kafka source config, UnmarshalConfig requires at least one broker address in the 'brokers' list. An empty or missing brokers list means the reader has nothing to connect to, so configuration is rejected with this message (the %s is the source name, 'kafka').

Source

Thrown at pkg/acquisition/modules/kafka/config.go:56

type KafkaBatchConfiguration struct {
	BatchMinBytes  int           `yaml:"min_bytes"`
	BatchMaxBytes  int           `yaml:"max_bytes"`
	BatchMaxWait   time.Duration `yaml:"max_wait"`
	BatchQueueSize int           `yaml:"queue_size"`
	CommitInterval time.Duration `yaml:"commit_interval"`
}

func (s *Source) UnmarshalConfig(yamlConfig []byte) error {
	s.Config = Configuration{}

	err := yaml.UnmarshalWithOptions(yamlConfig, &s.Config, yaml.Strict())
	if err != nil {
		return fmt.Errorf("cannot parse: %s", yaml.FormatError(err, false, false))
	}

	if len(s.Config.Brokers) == 0 {
		return fmt.Errorf("cannot create a %s reader with an empty list of broker addresses", s.GetName())
	}

	if s.Config.Topic == "" {
		return fmt.Errorf("cannot create a %s reader with an empty topic", s.GetName())
	}

	if s.Config.Mode == "" {
		s.Config.Mode = configuration.TAIL_MODE
	}

	s.logger.Debugf("successfully parsed kafka configuration : %+v", s.Config)

	return err
}

func (s *Source) Configure(_ context.Context, yamlConfig []byte, logger *log.Entry, metricsLevel metrics.AcquisitionMetricsLevel) error {
	s.logger = logger
	s.metricsLevel = metricsLevel

View on GitHub (pinned to 909b515798)

Solutions

Add at least one broker to the config: brokers: [kafka1:9092].
If brokers come from templating/env, verify the variable is populated at render time.
Ensure each entry is a host:port reachable from the crowdsec host.
Remove empty-string entries from the brokers list.

Example fix

// before
source: kafka
topic: crowdsec
// after
source: kafka
brokers:
  - localhost:9092
topic: crowdsec

Defensive patterns

Strategy: validation

Validate before calling

var kc struct {
    Brokers []string `yaml:"brokers"`
}
if err := yaml.Unmarshal(yamlCfg, &kc); err != nil { return err }
nonEmpty := 0
for _, b := range kc.Brokers { if strings.TrimSpace(b) != "" { nonEmpty++ } }
if nonEmpty == 0 { return errors.New("kafka source requires at least one broker") }

Try / catch

if err := source.UnmarshalConfig(cfg); err != nil {
    if strings.Contains(err.Error(), "empty list of broker addresses") {
        // inject brokers from env/templating and retry
    }
}

Prevention

Always include at least one brokers entry in kafka acquis blocks
Verify templated/env-provided broker values are non-empty at render time
Reachability-check each host:port before deployment

When it happens

Trigger: Source.UnmarshalConfig receiving a kafka YAML block with no 'brokers' key, an empty list ('brokers: []'), or a list containing only empty strings.

Common situations: Minimal example configs copied without the brokers line; templating that left the brokers field empty; forgetting to configure brokers because topic was set.

Understand the failure class

Background: "is required", "must be set", "missing required field": configuration validation errors across open-source libraries — this error's family across 36 libraries.

Related errors

AI-assisted analysis of crowdsecurity/crowdsec@909b515798 (2026-09-06). Data as JSON: /api/errors/585cf922483fe485. Report an issue: GitHub.