What causes "failed to read config file" in Netflix/chaosmonkey?

Check the wrapped viper error for the exact line/parse problem

failed to read config file

Error message

failed to read config file

What it means

Raised by config.Load when viper's ReadInConfig fails for a reason other than the file not existing — e.g. malformed TOML or an unreadable file. Missing files are deliberately tolerated and logged, so this error always indicates actual config-file corruption or I/O problems.

Source

Thrown at config/monkey.go:109

func Load(configPaths []string) (*Monkey, error) {
	m := &Monkey{v: viper.New()}

	m.setDefaults()
	m.setupEnvVarReader()

	for _, dir := range configPaths {
		m.v.AddConfigPath(dir)
	}

	m.v.SetConfigType("toml")
	m.v.SetConfigName("chaosmonkey")

	err := m.v.ReadInConfig()
	// It's ok if the config file doesn't exist, but we want to catch any
	// other config-related issues
	if err != nil {
		if !os.IsNotExist(err) {
			return nil, errors.Wrapf(err, "failed to read config file")
		}

		log.Printf("no config file found, proceeding without one")
	}

	err = m.configureRemote()
	if err != nil {
		return nil, err
	}
	return m, nil
}

// Defaults returns a Monkey config that just has the default values set
// it will not load local files or remote ones
func Defaults() *Monkey {
	v := &Monkey{v: viper.New()}
	v.setDefaults()
	return v

View on GitHub (pinned to eaa28fb761)

Solutions

Check the wrapped viper error for the exact line/parse problem
Run the file through a TOML linter/validator
Fix file permissions so the process user can read it
Confirm the config file path env var points to the intended file

Example fix

// before
cfg = monkey.toml
schedule_endpoint = "http://..."
// after
# valid TOML: quote the value and add newline
cfg = monkey.toml
schedule_endpoint = "http://..."

Defensive patterns

Strategy: validation

Validate before calling

f, err := os.Open(configPath)
if err != nil {
    log.Fatalf("config unreadable: %v", err)
}
f.Close()
// optionally pre-validate TOML with a parser before Load

Try / catch

m, err := config.Load(path)
if err != nil {
    if strings.Contains(err.Error(), "failed to read config file") {
        log.Fatalf("fix config at %s: %v", path, errors.Unwrap(err))
    }
    return err
}

Prevention

Lint TOML config in CI before deployment
Check file permissions after edits
Keep a known-good sample config
Validate config at deploy time, not runtime

When it happens

Trigger: Calling Load (via getConfig) when the config file exists but is unreadable (permissions) or contains syntax errors (invalid TOML).

Common situations: Config file with a TOML typo after an edit, file owned by root with 0600, symlink to a missing target, wrong CONFIG_PATH.

Related errors

AI-assisted analysis of Netflix/chaosmonkey@eaa28fb761 (2026-09-03). Data as JSON: /api/errors/bdcb6fbf5e41cc74. Report an issue: GitHub.