config

Config

This package handles configuration for Thelma.

It supports configuration through:

• a configuration file, located at ~/.thelma/config.yaml
• environment variables (eg. THELMA_HOME)

It uses Koanf under the hood to provide these features.

Usage

Declare a config struct. Then, unmarshal configuration into it at runtime using config.Unmarshal.

You can optionally:

• Set default values for fields using the default struct tag (via defaults library)
• Add validation to config values using the validate struct tag (via validator library)

Example

// Declare a config struct with optional default and validation tags
type LogConfig struct {
	Logging struct {
		Console struct {
			Level string `default:"info" validate:"oneof=trace debug info warn error"`
		}
		File struct {
			Enabled   bool   `default:"true"`
			Level     string `default:"debug" validate:"oneof=trace debug info warn error"`
			KeepFiles int    `description:"Number of rotated log files to keep" default:"5" validate:"gte=0"`
			MaxSizeMb int    `description:"Max size of rotated log files in megabytes" default:"8" validate:"gte=0"`
		}
	}
}

// Then use UnmarshalKey to unmarshal all config values under a given
// prefix into the struct.
func setupLogging(cfg config.Config) {
    var logConfig LogConfig
    if err := cfg.UnmarshalKey("logging", &logConfig) {
       // handle error
    }
    // initialize logging based on LogConfig settings
    logging.Level = logConfig.Level
    // ...
}

Root Configuration Values

Most clients of config will bundle all configuration under a unique key (eg. logging); this config should be deserialized into a struct using UnmarshalKey(). However, a few core, system-wide configuration values exist at the root level.

These include:

• home: refers to the path where terra-helmfile is checked out

These config values are retrieved using methods on the Config object itself. (eg. cfg.Home())

Only truly global, cross-cutting values that have implications for many parts of Thelma should be added at the root level.

Profiles

Thelma is run by humans, on laptops, as well as in CI/CD pipelines. Often it needs to behave slightly differently each situation. (For example, credentials should not be cached on disk on CI servers).

Thelma configuration values should default to the manual, run-by-people case. However, it's possible to set configuration overrides for the CI/CD case in the ci configuration profile, located in ./profiles/ci.yaml.

Thelma will automatically apply the ci profile when it is run in a non-interactive shell.

But it's possible to explicitly select a configuration profile using the THELMA_CONFIG_PROFILE environment variable:

# Run thelma with the default (i.e. "human-mode") config profile
THELMA_CONFIG_PROFILE=default thelma <...>

# Run thelma with the ci profile
THELMA_CONFIG_PROFILE=ci thelma <...>

FAQ

Why Koanf and not Viper?

Viper has a really unfortunate long-running bug where environment variables are ignored when unmarshalling config into a struct.

Although there are some hacky workarounds for the bug, they only work for Unmarshal(), and not UnmarshalKey(), because the two functions, for some reason, have very different implementations.

Koanf is not exposed as part of this package's API, so it should be relatively simple to migrate back to Viper if/when this issue is fixed.