goconfig

Overview ¶

Package cfgloader provides a wrapper for the koanf/v2 configuration package that make it easier to use for a preferred use case, configuring it to load values (in order) from yaml files, flags and environment variables.

Values are loaded in order from: - configuration files in the order given on the command line - environment variables - flags

If multiple sources contain different values for the same configruation field, the last one found is used.

In order for a structure field to be loaded, it must be exported (e.g start with a capital letter), and contain a koanf field tag:

type Config struct {
  Value  string         `koanf:"value"`
}

Values are loaded from all the sources based on the tag, and would be loaded from any of these sources if the were supplied:

$ export VALUE="from the environment" or $ ./prog -value="from a flag" or $ cat config.yaml value: from a config file

There are two strings that affect the loading of the configuration. There is a prefix which can be used to avoid collisons with environment variables.

If the prefix is set to "CONFIG_" when calling New, then the above example becomes:

$ export CONFIG_VALUE="from the environment"

Delimiter is used to separate nested configuration structures in flags:

type Nested struct {
  Val int `koanf:"val"`
}

type Config struct {
  Value  string `koanf:"value"`
  Nested Nested `koanf:"nested"`
}

With the delimiter set to ".", to set val, use: $ ./prog --nested.val=7

Environment variables always use "_" as their delimter, so without a prefix this would be:

$ export NESTED_VAL="from the environment"

Notes:

• This requires using the pflags package instead of the built in flags package.
• In order for flags to work, the flagset's Parse() routine must be called before calling Load()
• There are case sensitivities between the koanf struct tag, the flag name and the JSON field names. Some combinations work, but it is easiest to make them all match.