What causes "no syncs defined" in EugenMayer/docker-sync?

Add a top-level syncs: mapping with at least one named sync carrying a src: entry (src is mandatory per validate_sync_config, project_config.rb:89).

EugenMayer/docker-sync · error

no syncs defined

Error message

no syncs defined

What it means

After the version checks pass, validate_config! requires a top-level 'syncs' key and raises ERROR_MISSING_SYNCS ('no syncs defined') when it is absent (lib/docker-sync/config/project_config.rb:77). The check tests key presence only: syncs: {} (present but empty) passes validation and instead yields zero sync processes downstream. So this exact message means the syncs key itself is missing from the parsed config.

Solutions

Add a top-level syncs: mapping with at least one named sync carrying a src: entry (src is mandatory per validate_sync_config, project_config.rb:89).
Verify YAML indentation: syncs: must sit at column 0 with its sync entries indented beneath it.
If you intentionally want zero syncs for now, write syncs: {} so the key exists.

Example fix

# before
version: "2"

# after
version: "2"
syncs:
  appcode-sync:
    src: './src'

Defensive patterns

Strategy: validation

Validate before calling

require 'yaml'

raw = YAML.safe_load(File.read('docker-sync.yml')) || {}
abort 'docker-sync.yml: missing top-level syncs key' unless raw.key?('syncs')
warn 'syncs is empty: no sync processes will run' if raw['syncs'].to_a.empty?
config = DockerSync::ProjectConfig.new

Try / catch

begin
  DockerSync::ProjectConfig.new
rescue RuntimeError => e
  raise unless e.message == DockerSync::ProjectConfig::ERROR_MISSING_SYNCS
  # syncs key absent: add a top-level syncs: mapping with at least one entry
end

Prevention

After editing, parse docker-sync.yml to confirm syncs remains a top-level key.
One indentation level off silently nests syncs under another key; use a YAML-aware editor.
Give every sync entry at least src: when you create it, not later.

When it happens

Trigger: ProjectConfig.new with a config that has version: "2" but no top-level syncs: key: a file with only the header, entries nested under a misspelled key (sync:, syncs-config:), or sync entries pasted at the wrong indentation level so YAML demoted them.

Common situations: Half-finished first-time setup; YAML indentation mistakes that turn syncs into a nested key of something else; renaming the key while refactoring a config.

Related errors

AI-assisted analysis of EugenMayer/docker-sync@4eab6de164 (2026-08-23). Data as JSON: /api/errors/c29ea91d48bb0d42. Report an issue: GitHub.

Appendix: source

Thrown at lib/docker-sync/config/project_config.rb:77

      config['syncs'].any? { |name, sync_config|
        sync_config['sync_strategy'] == 'rsync'
      }
    end

    def fswatch_required?
      # noinspection RubyUnusedLocalVariable
      config['syncs'].any? { |name, sync_config|
        sync_config['watch_strategy'] == 'fswatch'
      }
    end

    private

      def validate_config!
        raise error_missing_given_config if config.nil?
        raise ERROR_MISSING_CONFIG_VERSION unless config.key?('version')
        raise ERROR_MISMATCH_CONFIG_VERSION unless config['version'].to_s == REQUIRED_CONFIG_VERSION
        raise ERROR_MISSING_SYNCS unless config.key?('syncs')

        validate_syncs_config!
      end

      def validate_syncs_config!
        config['syncs'].each do |name, sync_config|
          validate_sync_config(name, sync_config)
        end
      end

      def validate_sync_config(name, sync_config)
        config_mandatory = %w[src]
        #TODO: Implement autodisovery for other strategies
        config_mandatory.push('sync_host_port') if sync_config['sync_strategy'] == 'rsync'
        config_mandatory.each do |key|
          raise ("#{name} does not have #{key} configuration value set - this is mandatory") unless sync_config.key?(key)
        end
      end

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