Go configuration with fangs!
Many Go projects are built using Viper including:
Viper is a complete configuration solution for go applications including 12 factor apps. It is designed to work within an application, and can handle all types of configuration needs and formats. It supports:
Viper can be thought of as a registry for all of your applications configuration needs.
When building a modern application, you don’t want to worry about configuration file formats; you want to focus on building awesome software. Viper is here to help with that.
Viper does the following for you:
Viper uses the following precedence order. Each item takes precedence over the item below it:
Viper configuration keys are case insensitive.
A good configuration system will support default values. A default value is not required for a key, but it's useful in the event that a key hasn’t been set via config file, environment variable, remote configuration or flag.
Examples:
viper.SetDefault("ContentDir", "content")
viper.SetDefault("LayoutDir", "layouts")
viper.SetDefault("Taxonomies", map[string]string{"tag": "tags", "category": "categories"})
Viper requires minimal configuration so it knows where to look for config files. Viper supports JSON, TOML, YAML, HCL, and Java Properties files. Viper can search multiple paths, but currently a single Viper instance only supports a single configuration file. Viper does not default to any configuration search paths leaving defaults decision to an application.
Here is an example of how to use Viper to search for and read a configuration file. None of the specific paths are required, but at least one path should be provided where a configuration file is expected.
viper.SetConfigName("config") // name of config file (without extension) viper.AddConfigPath("/etc/appname/") // path to look for the config file in viper.AddConfigPath("$HOME/.appname") // call multiple times to add many search paths viper.AddConfigPath(".") // optionally look for config in the working directory err := viper.ReadInConfig() // Find and read the config file if err != nil { // Handle errors reading the config file panic(fmt.Errorf("Fatal error config file: %s \n", err)) }
Viper supports the ability to have your application live read a config file while running.
Gone are the days of needing to restart a server to have a config take effect, viper powered applications can read an update to a config file while running and not miss a beat.
Simply tell the viper instance to watchConfig. Optionally you can provide a function for Viper to run each time a change occurs.
Make sure you add all of the configPaths prior to calling WatchConfig()
viper.WatchConfig()
viper.OnConfigChange(func(e fsnotify.Event) {
fmt.Println("Config file changed:", e.Name)
})
Viper predefines many configuration sources such as files, environment variables, flags, and remote K/V store, but you are not bound to them. You can also implement your own required configuration source and feed it to viper.
viper.SetConfigType("yaml") // or viper.SetConfigType("YAML") // any approach to require this configuration into your program. var yamlExample = []byte(` Hacker: true name: steve hobbies: - skateboarding - snowboarding - go clothing: jacket: leather trousers: denim age: 35 eyes : brown beard: true `) viper.ReadConfig(bytes.NewBuffer(yamlExample)) viper.Get("name") // this would be "steve"
These could be from a command line flag, or from your own application logic.
viper.Set("Verbose", true)
viper.Set("LogFile", LogFile)
Aliases permit a single value to be referenced by multiple keys
viper.RegisterAlias("loud", "Verbose") viper.Set("verbose", true) // same result as next line viper.Set("loud", true) // same result as prior line viper.GetBool("loud") // true viper.GetBool("verbose") // true
Viper has full support for environment variables. This enables 12 factor applications out of the box. There are four methods that exist to aid working with ENV:
AutomaticEnv()
BindEnv(string...) : error
SetEnvPrefix(string)
SetEnvReplacer(string...) *strings.Replacer
When working with ENV variables, it’s important to recognize that Viper treats ENV variables as case sensitive.
Viper provides a mechanism to try to ensure that ENV variables are unique. By using SetEnvPrefix
, you can tell Viper to use add a prefix while reading from the environment variables. Both BindEnv
and AutomaticEnv
will use this prefix.
BindEnv
takes one or two parameters. The first parameter is the key name, the second is the name of the environment variable. The name of the environment variable is case sensitive. If the ENV variable name is not provided, then Viper will automatically assume that the key name matches the ENV variable name, but the ENV variable is IN ALL CAPS. When you explicitly provide the ENV variable name, it does not automatically add the prefix.
One important thing to recognize when working with ENV variables is that the value will be read each time it is accessed. Viper does not fix the value when the BindEnv
is called.
AutomaticEnv
is a powerful helper especially when combined with SetEnvPrefix
. When called, Viper will check for an environment variable any time a viper.Get
request is made. It will apply the following rules. It will check for a environment variable with a name matching the key uppercased and prefixed with the EnvPrefix
if set.
SetEnvReplacer
allows you to use a strings.Replacer
object to rewrite Env keys to an extent. This is useful if you want to use -
or something in your Get()
calls, but want your environmental variables to use _
delimiters. An example of using it can be found in viper_test.go
.
SetEnvPrefix("spf") // will be uppercased automatically BindEnv("id") os.Setenv("SPF_ID", "13") // typically done outside of the app id := Get("id") // 13
Viper has the ability to bind to flags. Specifically, Viper supports Pflags
as used in the Cobra library.
Like BindEnv
, the value is not set when the binding method is called, but when it is accessed. This means you can bind as early as you want, even in an init()
function.
The BindPFlag()
method provides this functionality.
Example:
serverCmd.Flags().Int("port", 1138, "Port to run Application server on")
viper.BindPFlag("port", serverCmd.Flags().Lookup("port"))
The use of pflag in Viper does not preclude the use of other packages that use the flag package from the standard library. The pflag package can handle the flags defined for the flag package by importing these flags. This is accomplished by a calling a convenience function provided by the pflag package called AddGoFlagSet().
Example:
package main
import (
"flag"
"github.com/spf13/pflag"
)
func main() {
pflag.CommandLine.AddGoFlagSet(flag.CommandLine)
pflag.Parse()
...
}
Viper provides two Go interfaces to bind other flag systems if you don't use Pflags
.
FlagValue
represents a single flag. This is a very simple example on how to implement this interface:
type myFlag struct {}
func (f myFlag) IsChanged() { return false }
func (f myFlag) Name() { return "my-flag-name" }
func (f myFlag) ValueString() { return "my-flag-value" }
func (f myFlag) ValueType() { return "string" }
Once your flag implements this interface, you can simply tell Viper to bind it:
viper.BindFlagValue("my-flag-name", myFlag{})
FlagValueSet
represents a group of flags. This is a very simple example on how to implement this interface:
type myFlagSet struct {
flags []myFlag
}
func (f myFlagSet) VisitAll(fn func(FlagValue)) {
for _, flag := range flags {
fn(flag)
}
}
Once your flag set implements this interface, you can simply tell Viper to bind it:
fSet := myFlagSet{
flags: []myFlag{myFlag{}, myFlag{}},
}
viper.BindFlagValues("my-flags", fSet)
To enable remote support in Viper, do a blank import of the viper/remote
package:
import _ "github.com/spf13/viper/remote"
Viper will read a config string (as JSON, TOML, YAML or HCL) retrieved from a path in a Key/Value store such as etcd or Consul. These values take precedence over default values, but are overridden by configuration values retrieved from disk, flags, or environment variables.
Viper uses crypt to retrieve configuration from the K/V store, which means that you can store your configuration values encrypted and have them automatically decrypted if you have the correct gpg keyring. Encryption is optional.
You can use remote configuration in conjunction with local configuration, or independently of it.
crypt
has a command-line helper that you can use to put configurations in your K/V store. crypt
defaults to etcd on http://127.0.0.1:4001.
$ go get github.com/xordataexchange/crypt/bin/crypt $ crypt set -plaintext /config/hugo.json /Users/hugo/settings/config.json
Confirm that your value was set:
$ crypt get -plaintext /config/hugo.json
See the crypt
documentation for examples of how to set encrypted values, or how to use Consul.
viper.AddRemoteProvider("etcd", "http://127.0.0.1:4001","/config/hugo.json") viper.SetConfigType("json") // because there is no file extension in a stream of bytes, supported extensions are "json", "toml", "yaml", "yml", "properties", "props", "prop" err := viper.ReadRemoteConfig()
viper.AddSecureRemoteProvider("etcd","http://127.0.0.1:4001","/config/hugo.json","/etc/secrets/mykeyring.gpg") viper.SetConfigType("json") // because there is no file extension in a stream of bytes, supported extensions are "json", "toml", "yaml", "yml", "properties", "props", "prop" err := viper.ReadRemoteConfig()
// alternatively, you can create a new viper instance. var runtime_viper = viper.New() runtime_viper.AddRemoteProvider("etcd", "http://127.0.0.1:4001", "/config/hugo.yml") runtime_viper.SetConfigType("yaml") // because there is no file extension in a stream of bytes, supported extensions are "json", "toml", "yaml", "yml", "properties", "props", "prop" // read from remote config the first time. err := runtime_viper.ReadRemoteConfig() // unmarshal config runtime_viper.Unmarshal(&runtime_conf) // open a goroutine to watch remote changes forever go func(){ for { time.Sleep(time.Second * 5) // delay after each request // currently, only tested with etcd support err := runtime_viper.WatchRemoteConfig() if err != nil { log.Errorf("unable to read remote config: %v", err) continue } // unmarshal new config into our runtime config struct. you can also use channel // to implement a signal to notify the system of the changes runtime_viper.Unmarshal(&runtime_conf) } }()
In Viper, there are a few ways to get a value depending on the value's type. The following functions and methods exist:
Get(key string) : interface{}
GetBool(key string) : bool
GetFloat64(key string) : float64
GetInt(key string) : int
GetString(key string) : string
GetStringMap(key string) : map[string]interface{}
GetStringMapString(key string) : map[string]string
GetStringSlice(key string) : []string
GetTime(key string) : time.Time
GetDuration(key string) : time.Duration
IsSet(key string) : bool
One important thing to recognize is that each Get function will return a zero value if it’s not found. To check if a given key exists, the IsSet()
method has been provided.
Example:
viper.GetString("logfile") // case-insensitive Setting & Getting if viper.GetBool("verbose") { fmt.Println("verbose enabled") }
The accessor methods also accept formatted paths to deeply nested keys. For example, if the following JSON file is loaded:
{ "host": { "address": "localhost", "port": 5799 }, "datastore": { "metric": { "host": "127.0.0.1", "port": 3099 }, "warehouse": { "host": "198.0.0.1", "port": 2112 } } }
Viper can access a nested field by passing a .
delimited path of keys:
GetString("datastore.metric.host") // (returns "127.0.0.1")
This obeys the precedence rules established above; the search for the root key (in this example, datastore
) will cascade through the remaining configuration registries until found. The search for the sub-keys (metric
and host
), however, will not.
For example, if the metric
key was not defined in the configuration loaded from file, but was defined in the defaults, Viper would return the zero value.
On the other hand, if the primary key was not defined, Viper would go through the remaining registries looking for it.
Lastly, if there exists a key that matches the delimited key path, its value will be returned instead. E.g.
{ "datastore.metric.host": "0.0.0.0", "host": { "address": "localhost", "port": 5799 }, "datastore": { "metric": { "host": "127.0.0.1", "port": 3099 }, "warehouse": { "host": "198.0.0.1", "port": 2112 } } } GetString("datastore.metric.host") //returns "0.0.0.0"
Extract sub-tree from Viper.
For example, viper
represents:
app: cache1: max-items: 100 item-size: 64 cache2: max-items: 200 item-size: 80
After executing:
subv := viper.Sub("app.cache1")
subv
represents:
max-items: 100 item-size: 64
Suppose we have:
func NewCache(cfg *Viper) *Cache {...}
which creates a cache based on config information formatted as subv
. Now it's easy to create these 2 caches separately as:
cfg1 := viper.Sub("app.cache1")
cache1 := NewCache(cfg1)
cfg2 := viper.Sub("app.cache2")
cache2 := NewCache(cfg2)
You also have the option of Unmarshaling all or a specific value to a struct, map, etc.
There are two methods to do this:
Unmarshal(rawVal interface{}) : error
UnmarshalKey(key string, rawVal interface{}) : error
Example:
type config struct {
Port int
Name string
PathMap string `mapstructure:"path_map"`
}
var C config
err := Unmarshal(&C)
if err != nil {
t.Fatalf("unable to decode into struct, %v", err)
}
Viper comes ready to use out of the box. There is no configuration or initialization needed to begin using Viper. Since most applications will want to use a single central repository for their configuration, the viper package provides this. It is similar to a singleton.
In all of the examples above, they demonstrate using viper in it's singleton style approach.
You can also create many different vipers for use in your application. Each will have it’s own unique set of configurations and values. Each can read from a different config file, key value store, etc. All of the functions that viper package supports are mirrored as methods on a viper.
Example:
x := viper.New() y := viper.New() x.SetDefault("ContentDir", "content") y.SetDefault("ContentDir", "foobar") //...
When working with multiple vipers, it is up to the user to keep track of the different vipers.
Q: Why not INI files?
A: Ini files are pretty awful. There’s no standard format, and they are hard to validate. Viper is designed to work with JSON, TOML or YAML files. If someone really wants to add this feature, I’d be happy to merge it. It’s easy to specify which formats your application will permit.
Q: Why is it called “Viper”?
A: Viper is designed to be a companion to Cobra. While both can operate completely independently, together they make a powerful pair to handle much of your application foundation needs.
Q: Why is it called “Cobra”?
A: Is there a better name for a commander?