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Composable, observable and performant config handling for Go for the distributed processing era
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README.md

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Konfig

Composable, observable and performant config handling for Go. Written for larger distributed systems where you may have plenty of configuration sources - it allows you to compose configurations from multiple sources with reload hooks making it simple to build apps that live in a highly dynamic environment.

What's up with the name?

The name is Swedish for "config". We have a lot of nationalities here at Lalamove and to celebrate cultural diversity most of our open source packages will carry a name derived from a non-English language that is perhaps spoken by at least one of our employees(?).

Why another config package?

Most config packages for Golang are not very extensible and rarely expose interfaces. This makes it complex to build apps which can reload their state dynamically and difficult to mock. Fewer still come with sources such as Vault, Etcd and multiple encoding formats. In short, we didn't find a package that satisfied all of our requirements when we started out.

konfig is built around 4 small interfaces:

  • Loader
  • Watcher
  • Parser
  • Closer

Konfig features include:

  • Dynamic configuration loading
  • Composable load configs from multiple sources, such as vault, files and etcd
  • Polyglot load configs from multiple format. Konfig supports JSON, YAML, TOML, Key=Value
  • Fast, Lock-free, Thread safe Read Reads are up to 10x faster than Viper
  • Observable config - Hot Reload mechanism and tooling to manage state
  • Typed Read get typed values from config or bind a struct
  • Metrics exposed prometheus metrics telling you how many times a config is reloaded, if it failed, and how long it takes to reload

Get started

go get github.com/lalamove/konfig

Load and watch a json formatted config file.

var configFiles = []klfile.File{
	{
		Path: "./config.json",
		Parser: kpjson.Parser,
	},
}

func init() {
	konfig.Init(konfig.DefaultConfig())
}

func main() {
	// load from json file	
	konfig.RegisterLoaderWatcher(
		klfile.New(&klfile.Config{
			Files: 			configFiles,
			Watch: 			true,
		}),
		// optionally you can pass config hooks to run when a file is changed
		func(c Store) error {
			return nil	
		},
	)

	if err := konfig.LoadWatch(); err != nil {
		log.Fatal(err)
	}

	// retrieve value from config file
	konfig.Bool("debug")
}

Store

The Store is the base of the config package. It holds and gives access to values stored by keys.

Creating a Store

You can create a global Store by calling konfig.Init(*konfig.Config):

konfig.Init(konfig.DefaultConfig())

The global store is accessible directly from the package:

konfig.Get("foo") // calls store.Get("foo")

You can create a new store by calling konfig.New(*konfig.Config):

s := konfig.New(konfig.DefaultConfig())

Loading and Watching a Store

After registering Loaders and Watchers in the konfig.Store, you must load and watch the store.

You can do both by calling LoadWatch:

if err := konfig.LoadWatch(); err != nil {
    log.Fatal(err)
}

You can call Load only, it will load all loaders and return:

if err := konfig.Load(); err != nil {
    log.Fatal(err)
}

And finally you can call Watch only, it will start all watchers and return:

if err := konfig.Watch(); err != nil {
    log.Fatal(err)
}

Loaders

Loaders load config values into the store. A loader is an implementation of the loader interface.

type Loader interface {
    // Name return the name of the load, it is used to create labeled vectors metrics per loader
    Name() string
    // StopOnFailure indicates if a failure of the loader should trigger a stop
    StopOnFailure() bool
	// Loads the config and add it to the Store
	Load(Store) error
	// MaxRetry returns the maximum number of times to allow retrying on load failure
	MaxRetry() int
	// RetryDelay returns the delay to wait before retrying
	RetryDelay() time.Duration
}

You can register loaders in the config individually or with a watcher.

Register a loader by itself:

configLoader := konfig.RegisterLoader(
	klfile.New(
 		&klfile.Config{
			Files: []klfile.File{
				{
					Parser: kpjson.Parser,
					Path: "./konfig.json",
				},
			},
		},
	),
)

Register a loader with a watcher:

To register a loader and a watcher together, you must register a LoaderWatcher which is an interface that implements both the Loader and the Watcher interface.

configLoader := konfig.RegisterLoaderWatcher(
	klfile.New(
 		&klfile.Config{
			Files: []klfile.File{
				{
					Parser: kpjson.Parser,
					Path: "./konfig.json",
				},
			},
			Watch: true,
		},
	),
)

You can also compose a loader and a watcher to create a LoaderWatcher:

configLoader := konfig.RegisterLoaderWatcher(
	// it creates a LoaderWatcher from a loader and a watcher
	konfig.NewLoaderWatcher(
		someLoader,
		someWatcher,
	),
)

Built in loaders

Konfig already has the following loaders, they all have a built in watcher:

Loads configs from files which can be watched. Files can have different parsers to load different formats. It has a built in file watcher which triggers a config reload (running hooks) when files are modified.

Loads configs from vault secrets. It has a built in Poll Watcher which triggers a config reload (running hooks) before the secret and the token from the auth provider expires.

Loads configs from HTTP sources. Sources can have different parsers to load different formats. It has a built in Poll Diff Watcher which triggers a config reload (running hooks) if data is different.

Loads configs from Etcd keys. Keys can have different parser to load different formats. It has a built in Poll Diff Watcher which triggers a config reload (running hooks) if data is different.

Loads configs from Consul KV. Keys can have different parser to load different formats. It has built in Poll Diff Watcher which triggers a config reload (running hooks) if data is different.

Loads configs from environment variables.

Loads configs from command line flags.

Parsers

Parsers parse an io.Reader into a konfig.Store. These are used by some loaders to parse the data they fetch into the config store. the File Loader, Etcd Loader and HTTP Loader use Parsers.

Config already has the following parsers:

Watchers

Watchers trigger a call on a Loader on events. A watcher is an implementation of the Watcher interface.

type Watcher interface {
	// Start starts the watcher, it must not be blocking.
	Start() error
	// Done indicate whether the watcher is done or not
	Done() <-chan struct{}
	// Watch should block until an event unlocks it
	Watch() <-chan struct{}
	// Close closes the watcher, it returns a non nil error if it is already closed
	// or something prevents it from closing properly.
	Close() error
    // Err returns the error attached to the watcher
    Err() error
}

Built in watchers

Konfig already has the following watchers:

Watches files for changes.

Sends events at a given rate, or if diff is enabled. It takes a Getter and fetches the data at a given rate. If data is different, it sends an event.

Hooks

Hooks are functions ran after a successful loader Load() call. They are used to reload the state of the application on a config change.

Registering a loader with some hooks

You can register a loader or a loader watcher with hooks.

configLoader := konfig.RegisterLoaderWatcher(
	klfile.New(
 		&klfile.Config{
			Files: []klfile.File{
				{
					Parser: yamlparser.Parser,
					Path: "./konfig.yaml",
				},
			},
			Watch: true,
		},
	),
	func(s konfig.Store) error {
		// Here you should reload the state of your app
		return nil
	},
)

Adding hooks to an existing loader

You can register a Loader or a LoaderWatcher with hooks.

configLoader.AddHooks(
	func(s konfig.Store) error {
		// Here you should reload the state of your app	
		return nil
	},
	func(s konfig.Store) error {
		// Here you should reload the state of your app	
		return nil
	},
)

Adding hooks on keys

Alternatively, you can add hooks on keys. Hooks on keys will match for prefix in order to run a hook when any key with a given prefix is updated. A hook can only be run once per load event, even if multiple keys match that hook.

konfig.RegisterKeyHook(
    "db.",
    func(s konfig.Store) error {
        return nil
    },
)

Closers

Closers can be added to konfig so that if konfig fails to load, it will execute Close() on the registered Closers.

type Closer interface {
	Close() error
}

Register a Closer

konfig.RegisterCloser(closer)

Config Groups

You can namespace your configs using config Groups.

konfig.Group("db").RegisterLoaderWatcher(	
	klfile.New(
 		&klfile.Config{
			Files: []klfile.File{
				{
					Parser: yamlparser.Parser,
					Path: "./db.yaml",
				},
			},
			Watch: true,
		},
	),
)

// accessing grouped config 
dbHost := konfig.Group("db").MustString("credentials.host")

Binding a Type to a Store

You can bind a type to the konfig store if you want your config values to be unmarshaled to a struct or a map[string]interface{}. Then you can access an instance of that type in a thread safe manner (in order to be safe for dynamic config updates).

Let's see with an example of a json config file:

{
    "addr": ":8080",
    "debug": true,
    "db": {
        "username": "foo"
    },
    "redis": {
        "host": "127.0.0.1"
    }
}
type DBConfig struct {
    Username string
}
type Config struct {
    Addr        string
    Debug       string
    DB          DBConfig `konfig:"db"`
    RedisHost   string `konfig:"redis.host"`
}

// we init the root konfig store
konfig.Init(konfig.DefaultConfig())

// we bind the Config struct to the konfig.Store
konfig.Bind(Config{})

// we register our config file
konfig.RegisterLoaderWatcher(
	klfile.New(
 		&klfile.Config{
			Files: []klfile.File{
				{
					Parser: kpjson.Parser,
					Path: "./config.json",
				},
			},
			Watch: true,
		},
	),
)

// we load our config and start watching
if err := konfig.LoadWatch(); err != nil {
    log.Fatal(err)
}

// Get our config value
c := konfig.Value().(Config)

fmt.Println(c.Addr) // :8080

Note that you can compose your config sources. For example, have your credentials come from Vault and be renewed often and have the rest of your config loaded from a file and be updated on file change.

It is important to understand how Konfig unmarshals your config values into your struct. When a Loader calls konfig.Set(), if the konfig store has a value bound to it, it will try to unmarshal the key to the bound value.

  • First, it will look for field tags in the struct, if a tag matches exactly the key, it will unmarshal the key to the struct field.
  • Then, it will do a EqualFold on the field name and the key, if they match, it will unmarshal the key to the struct field.
  • Then, if the key has a dot, it will check if the tag or the field name (to lowercase) is a prefix of the key, if yes, it will check if the type of the field is a struct of pointer, if yes, it will check the struct using what's after the prefix as the key.

Read from config

Apart from reading from the bound config value, konfig provides several methods to read values.

Every method to retrieve config values come in 2 flavours:

  • Get reads a value at the given key. If key is not present it returns the zero value of the type.
  • MustGet reads a value at the given key. If key is not present it panics.

All methods to read values from a Store:

// Exists checks whether the key k is set in the store.
Exists(k string) bool

// Get gets the value with the key k fron the store. If the key is not set, Get returns nil. To check whether a value is really set, use Exists.
Get(k string) interface{}
// MustGet tries to get the value with the key k from the store. If the key k does not exist in the store, MustGet panics.
MustGet(k string) interface{}

// MustString tries to get the value with the key k from the store and casts it to a string. If the key k does not exist in the store, MustString panics.
MustString(k string) string
// String tries to get the value with the key k from the store and casts it to a string. If the key k does not exist it returns the Zero value.
String(k string) string

// MustInt tries to get the value with the key k from the store and casts it to a int. If the key k does not exist in the store, MustInt panics.
MustInt(k string) int
// Int tries to get the value with the key k from the store and casts it to a int. If the key k does not exist it returns the Zero value.
Int(k string) int

// MustFloat tries to get the value with the key k from the store and casts it to a float. If the key k does not exist in the store, MustFloat panics.
MustFloat(k string) float64
// Float tries to get the value with the key k from the store and casts it to a float. If the key k does not exist it returns the Zero value.
Float(k string) float64

// MustBool tries to get the value with the key k from the store and casts it to a bool. If the key k does not exist in the store, MustBool panics.
MustBool(k string) bool
// Bool tries to get the value with the key k from the store and casts it to a bool. If the key k does not exist it returns the Zero value.
Bool(k string) bool

// MustDuration tries to get the value with the key k from the store and casts it to a time.Duration. If the key k does not exist in the store, MustDuration panics.
MustDuration(k string) time.Duration
// Duration tries to get the value with the key k from the store and casts it to a time.Duration. If the key k does not exist it returns the Zero value.
Duration(k string) time.Duration

// MustTime tries to get the value with the key k from the store and casts it to a time.Time. If the key k does not exist in the store, MustTime panics.
MustTime(k string) time.Time
// Time tries to get the value with the key k from the store and casts it to a time.Time. If the key k does not exist it returns the Zero value.
Time(k string) time.Time

// MustStringSlice tries to get the value with the key k from the store and casts it to a []string. If the key k does not exist in the store, MustStringSlice panics.
MustStringSlice(k string) []string
// StringSlice tries to get the value with the key k from the store and casts it to a []string. If the key k does not exist it returns the Zero value.
StringSlice(k string) []string

// MustIntSlice tries to get the value with the key k from the store and casts it to a []int. If the key k does not exist in the store, MustIntSlice panics.
MustIntSlice(k string) []int
// IntSlice tries to get the value with the key k from the store and casts it to a []int. If the key k does not exist it returns the Zero value.
IntSlice(k string) []int

// MustStringMap tries to get the value with the key k from the store and casts it to a map[string]interface{}. If the key k does not exist in the store, MustStringMap panics.
MustStringMap(k string) map[string]interface{}
// StringMap tries to get the value with the key k from the store and casts it to a map[string]interface{}. If the key k does not exist it returns the Zero value.
StringMap(k string) map[string]interface{}

// MustStringMapString tries to get the value with the key k from the store and casts it to a map[string]string. If the key k does not exist in the store, MustStringMapString panics.
MustStringMapString(k string) map[string]string
// StringMapString tries to get the value with the key k from the store and casts it to a map[string]string. If the key k does not exist it returns the Zero value.
StringMapString(k string) map[string]string 

Strict Keys

You can define required keys on the konfig.Store by calling the Strict method. When calling strict method, konfig will set required keys on the store and during the first Load call on the store it will check if the keys are present, if not, Load will return a non nil error. Then, after every Load on a loader, konfig will check again if the keys are still present, if not, the loader Load will be considered a failure.

Usage:

// We init the root konfig store
konfig.Init(konfig.DefaultConfig()).Strict("debug", "username")

// Register our loaders
...

// We load our config and start watching.
// If strict keys are not found after the load operation, LoadWatch will return a non nil error. 
if err := konfig.LoadWatch(); err != nil {
    log.Fatal(err)
}

Getter

To easily build services which can use dynamically loaded configs you can create getters for specific keys. A getter implements ngetter.GetterTyped from nui package. It is useful when building apps in larger distributed environments.

Example with a config value set for the debug key:

debug := konfig.Getter("debug")

debug.Bool() // true

Metrics

Konfig comes with prometheus metrics.

Two metrics are exposed:

  • Config reloads counter vector with labels
  • Config reload duration summary vector with labels

Example of metrics:

# HELP konfig_loader_reload Number of config loader reload
# TYPE konfig_loader_reload counter
konfig_loader_reload{loader="config-files",result="failure",store="root"} 0.0
konfig_loader_reload{loader="config-files",result="success",store="root"} 1.0

# HELP konfig_loader_reload_duration Histogram for the config reload duration
# TYPE konfig_loader_reload_duration summary
konfig_loader_reload_duration{loader="config-files",store="root",quantile="0.5"} 0.001227641
konfig_loader_reload_duration{loader="config-files",store="root",quantile="0.9"} 0.001227641
konfig_loader_reload_duration{loader="config-files",store="root",quantile="0.99"} 0.001227641
konfig_loader_reload_duration_sum{loader="config-files",store=""} 0.001227641
konfig_loader_reload_duration_count{loader="config-files",store=""} 1.0

To enable metrics, you must pass a custom config when creating a config store:

konfig.Init(&konfig.Config{
    Metrics: true,
    Name: "root",
})

Benchmark

Benchmarks are run on viper, go-config and konfig. Benchmark are done on reading ops and show that Konfig is 0 allocs on read and at leat 3x fastet than Viper:

cd benchmarks && go test -bench . && cd ../
goos: linux
goarch: amd64
pkg: github.com/lalamove/konfig/benchmarks
BenchmarkGetKonfig-4            200000000                7.75 ns/op            0 B/op          0 allocs/op
BenchmarkStringKonfig-4         30000000                49.9 ns/op             0 B/op          0 allocs/op
BenchmarkGetViper-4             20000000               101 ns/op              32 B/op          2 allocs/op
BenchmarkStringViper-4          10000000               152 ns/op              32 B/op          2 allocs/op
BenchmarkGetGoConfig-4          10000000               118 ns/op              40 B/op          3 allocs/op
BenchmarkStringGoConfig-4       10000000               125 ns/op              40 B/op          3 allocs/op
PASS

Contributing

Contributions are welcome. To make contributions, fork the repository, create a branch and submit a Pull Request to the master branch.

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