fluent/fluentd · error · Fluent::ConfigError

# . Service must have `host` and `port

Error message

#{e}. Service must have `host` and `port`

What it means

SdFileServiceDiscovery#fetch_server_info (lib/fluent/plugin/sd_file.rb:138) maps each YAML/JSON service entry to a Service object using Hash#fetch for 'host' and 'port' — which raise KeyError when absent — and re-wraps that as Fluent::ConfigError. Entries may omit every other field (name, weight, standby, username...) but host and port are mandatory. The error names the missing key in its message.

Solutions

1. Add host and port to every entry: - host: 192.0.2.1\\n port: 24224.
2. Validate the file shape before restart (yaml parse + each entry has_key host/port).
3. Regenerate the file from source data with the correct field mapping.
4. Use fluentd --dry-run to fail fast at deploy time instead of at runtime reload.

Example fix

# before
# /etc/fluent/services.yaml
- name: node1
- name: node2
  host: 192.0.2.2
  port: 24224
# after
- name: node1
  host: 192.0.2.1
  port: 24224
- name: node2
  host: 192.0.2.2
  port: 24224

require 'yaml'
YAML.load_file('/etc/fluent/services.yaml').each do |s|
  abort "entry missing host/port: #{s}" unless s['host'] && s.key?('port')
end

def complete_service_entry?(s)
  s.is_a?(Hash) && s.key?('host') && s.key?('port')
end

When it happens

Trigger: A services.yaml entry like '- name: node1' (no host/port); port specified as a string key 'port:' with empty value yielding nil is accepted, but truly absent keys raise; JSON entries where host is nested one level deeper than expected; entries using 'address' instead of 'host'.

Common situations: Hand-editing service discovery YAML and forgetting the port; generating the file from a CMDB export with different field names; truncated YAML from a failed template render; mixing indentation so entries land under a comments/metadata key.

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

• sd_file: path=# couldn't open #
• sd_file: path=# not found
• both of utc and localtime are specified, use only one of…
• ca_private_key_path is required when ca_cert_path is…
• Cannot enable FIPS compliant mode. OpenSSL FIPS…

AI-assisted analysis of fluent/fluentd@dd45c6e18d (2026-08-21). Data as JSON: /api/errors/f06754e28f45712a. Report an issue: GitHub.

Appendix: source

Thrown at lib/fluent/plugin/sd_file.rb:138

          rescue => e
            raise Fluent::ConfigError, "sd_file: path=#{@path} couldn't open #{e}"
          end

        parser.call(config_data).map do |s|
          Service.new(
            :file,
            s.fetch('host'),
            s.fetch('port'),
            s['name'],
            s.fetch('weight', DEFAULT_WEIGHT),
            s['standby'],
            s['username'],
            s['password'],
            s['shared_key'],
          )
        end
      rescue KeyError => e
        raise Fluent::ConfigError, "#{e}. Service must have `host` and `port`"
      end

      class StatWatcher < Coolio::StatWatcher
        def initialize(path, log, &callback)
          @path = path
          @log = log
          @callback = callback
          super(@path)
        end

        def on_change(prev_stat, cur_stat)
          @callback.call(prev_stat, cur_stat)
        rescue => e
          @log.error(e)
        end
      end
    end
  end

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