Elixir SDK Reference

ConfigCat Elixir SDK on GitHub

Getting started

1. Add configcat to your list of dependencies in mix.exs

def deps do
  [
    {:configcat, "~> 2.0.0"}
  ]
end

2. Add ConfigCat to your application Supervisor tree

def start(_type, _args) do
  children = [
    {ConfigCat, [sdk_key: "YOUR SDK KEY"]},
    MyApp
  ]

  opts = [strategy: :one_for_one, name: MyApp.Supervisor]
  Supervisor.start_link(children, opts)
end

3. Get your setting value

isMyAwesomeFeatureEnabled = ConfigCat.get_value("isMyAwesomeFeatureEnabled", false)
if isMyAwesomeFeatureEnabled do
    do_the_new_thing()
else
    do_the_old_thing()
end

Setting up the ConfigCat Client

ConfigCat Client is responsible for:

• managing the communication between your application and ConfigCat servers.
• caching your setting values and feature flags.
• serving values quickly in a failsafe way.

{ConfigCat, options} returns a client with default options.

Properties	Description
sdk_key	REQUIRED. SDK Key to access your feature flags and configurations. Get it from ConfigCat Dashboard.
data_governance	Describes the location of your feature flag and setting data within the ConfigCat CDN. This parameter needs to be in sync with your Data Governance preferences. Defaults to :global. More about Data Governance. Available options: :global, :eu_only.
cache_policy	CachePolicy.auto/1, CachePolicy.lazy/1 and CachePolicy.manual/0. Defaults to: CachePolicy.auto/0 See See below for details.
cache	Caching module you want configcat to use. Defaults to: ConfigCat.InMemoryCache.
http_proxy	Specify this option if you need to use a proxy server to access your ConfigCat settings. You can provide a simple URL, like https://my_proxy.example.com or include authentication information, like https://user:[email protected]_proxy.example.com/.
connect_timeout	Timeout for establishing a TCP or SSL connection, in milliseconds. Default is 8000.
read_timeout	Timeout for receiving an HTTP response from the socket, in milliseconds. Default is 5000.
flag_overrides	Local feature flag & setting overrides. More about feature flag overrides
name	A unique identifier for this instance of ConfigCat. Defaults to ConfigCat. Must be provided if you need to run more than one instance of ConfigCat in the same application. If you provide a name, you must then pass that name to all of the API functions using the client option.

Anatomy of get_value()

Parameters	Description
key	REQUIRED. Setting-specific key. Set on ConfigCat Dashboard for each setting.
default_value	REQUIRED. This value will be returned in case of an error.
user	Optional, ConfigCat.User Object. Essential when using Targeting. Read more about Targeting.
client	If you are running multiple instances of ConfigCat, provide the client: :unique_name option, specifying the name of the instance which you want to access.

value = ConfigCat.get_value(
    "keyOfMySetting", # Setting Key
    false, # Default value
    ConfigCat.User.new("#UNIQUE-USER-IDENTIFIER#") # Optional User Object
);

User Object

The User Object is essential if you'd like to use ConfigCat's Targeting feature.

user_object = ConfigCat.User.new("#UNIQUE-USER-IDENTIFIER#")
user_object = ConfigCat.User.new("[email protected]")

Parameters	Description
identifier	REQUIRED. Unique identifier of a user in your application. Can be any value, even an email address.
email	Optional parameter for easier targeting rule definitions.
country	Optional parameter for easier targeting rule definitions.
custom	Optional Map for custom attributes of a user for advanced targeting rule definitions. e.g. User role, Subscription type.

user_object = ConfigCat.User.new("#UNIQUE-USER-IDENTIFIER#", email: "[email protected]", country: "United Kingdom",
                custom: %{SubscriptionType: "Pro", UserRole: "Admin"})

Polling Modes

The ConfigCat SDK supports 3 different polling mechanisms to acquire the setting values from ConfigCat. After latest setting values are downloaded, they are stored in the internal cache then all get_value() calls are served from there. With the following polling modes, you can customize the SDK to best fit to your application's lifecycle.
More about polling modes.

Auto polling (default)

The ConfigCat SDK downloads the latest values and stores them automatically every 60 seconds.

Use the poll_interval_seconds option parameter to change the polling interval.

{ConfigCat, [
    sdk_key: "YOUR SDK KEY",
    cache_policy: ConfigCat.CachePolicy.auto(poll_interval_seconds: 60)
]},

Adding a callback to on_changed option parameter will get you notified about changes.

{ConfigCat, [
    sdk_key: "YOUR SDK KEY",
    cache_policy: ConfigCat.CachePolicy.auto(on_changed: callback)
]}

Available options:

Option Parameter	Description	Default
poll_interval_seconds	Polling interval.	60
on_changed	A 0-arity function to be called about configuration changes. Needs to run on a separate proccess. Any exceptions raised by on_changed are caught and logged.	-

Lazy loading

When calling get_value() the ConfigCat SDK downloads the latest setting values if they are not present or expired in the cache. In this case the get_value() will return the setting value after the cache is updated.

Use cache_expiry_seconds option parameter to set cache lifetime.

{ConfigCat, [
    sdk_key: "YOUR SDK KEY",
    cache_policy: ConfigCat.CachePolicy.lazy(cache_expiry_seconds: 300)
]}

Available options:

Option Parameter	Description	Default
cache_expiry_seconds	Cache TTL.	60

Manual polling

Manual polling gives you full control over when the config JSON (with the setting values) is downloaded. ConfigCat SDK will not update them automatically. Calling force_refresh() is your application's responsibility.

ConfigCat.force_refresh()

get_value() returns default_value if the cache is empty. Call force_refresh() to update the cache.

value = ConfigCat.get_value("key", "my default value") # Returns "my default value"
ConfigCat.force_refresh();
value = ConfigCat.get_value("key", "my default value") # Returns "value from server"

Custom cache behaviour with cache: option parameter

To be able to customize the caching layer you need to implement the following behaviour:

defmodule ConfigCat.ConfigCache do
  alias ConfigCat.Config

  @type key :: String.t()
  @type result :: {:ok, Config.t()} | {:error, :not_found}

  @callback get(key) :: {:ok, Config.t()} | {:error, :not_found}
  @callback set(key, Config.t()) :: :ok
end

• You must implement (either explicitly or implicitly) the ConfigCache behaviour
• It is the responsibility of the calling application to supervise the cache if it needs to be supervised.

Multiple ConfigCat instances

If you need to run more than one instance of ConfigCat, you can add multiple ConfigCat children. You will need to give ConfigCat a unique name option for each, as well as using Supervisor.child_spec/2 to provide a unique id for each instance.

# lib/my_app/application.ex
def start(_type, _args) do
  children = [
    # ... other children ...
    Supervisor.child_spec({ConfigCat, [sdk_key: "sdk_key_1", name: :first]}),
    Supervisor.child_spec({ConfigCat, [sdk_key: "sdk_key_2", name: :second]}),
  ]
  opts = [strategy: :one_for_one, name: MyApp.Supervisor]
  Supervisor.start_link(children, opts)
end

Then you can call .get_value/4 like this:

ConfigCat.get_value("setting", "default", client: :first)
ConfigCat.get_value("setting", "default", client: :second)

Flag Overrides

With flag overrides you can overwrite the feature flags & settings downloaded from the ConfigCat CDN with local values. Moreover, you can specify how the overrides should apply over the downloaded values. The following 3 behaviours are supported:

• Local/Offline mode (:local_only): When evaluating values, the SDK will not use feature flags & settings from the ConfigCat CDN, but it will use all feature flags & settings that are loaded from local-override sources.

• Local over remote (:local_over_remote): When evaluating values, the SDK will use all feature flags & settings that are downloaded from the ConfigCat CDN, plus all feature flags & settings that are loaded from local-override sources. If a feature flag or a setting is defined both in the downloaded and the local-override source then the local-override version will take precedence.

• Remote over local (:remote_over_local): When evaluating values, the SDK will use all feature flags & settings that are downloaded from the ConfigCat CDN, plus all feature flags & settings that are loaded from local-override sources. If a feature flag or a setting is defined both in the downloaded and the local-override source then the downloaded version will take precedence.

You can set up the SDK to load your feature flag & setting overrides from a file or a map.

JSON File

The SDK can load your feature flag & setting overrides from a file.

File

{ConfigCat, [
    sdk_key: "YOUR SDK KEY",
    flag_overrides: ConfigCat.LocalFileDataSource.new(
      "path/to/the/local_flags.json",  # path to the file
      :local_only  # local/offline mode
    )
]}

JSON File Structure

The SDK supports 2 types of JSON structures to describe feature flags & settings.

1. Simple (key-value) structure

{
  "flags": {
    "enabledFeature": true,
    "disabledFeature": false,
    "intSetting": 5,
    "doubleSetting": 3.14,
    "stringSetting": "test"
  }
}

2. Complex (full-featured) structure

This is the same format that the SDK downloads from the ConfigCat CDN. It allows the usage of all features you can do on the ConfigCat Dashboard.

You can download your current config JSON from ConfigCat's CDN and use it as a baseline.

The URL to your current config JSON is based on your Data Governance settings:

• GLOBAL: https://cdn-global.configcat.com/configuration-files/{YOUR-SDK-KEY}/config_v5.json
• EU: https://cdn-eu.configcat.com/configuration-files/{YOUR-SDK-KEY}/config_v5.json

{
  "f": {
    // list of feature flags & settings
    "isFeatureEnabled": {
      // key of a particular flag
      "v": false, // default value, served when no rules are defined
      "i": "430bded3", // variation id (for analytical purposes)
      "t": 0, // feature flag's type, possible values:
      // 0 -> BOOLEAN
      // 1 -> STRING
      // 2 -> INT
      // 3 -> DOUBLE
      "p": [
        // list of percentage rules
        {
          "o": 0, // rule's order
          "v": true, // value served when the rule is selected during evaluation
          "p": 10, // % value
          "i": "bcfb84a7" // variation id (for analytical purposes)
        },
        {
          "o": 1, // rule's order
          "v": false, // value served when the rule is selected during evaluation
          "p": 90, // % value
          "i": "bddac6ae" // variation id (for analytical purposes)
        }
      ],
      "r": [
        // list of targeting rules
        {
          "o": 0, // rule's order
          "a": "Identifier", // comparison attribute
          "t": 2, // comparator, possible values:
          // 0  -> 'IS ONE OF',
          // 1  -> 'IS NOT ONE OF',
          // 2  -> 'CONTAINS',
          // 3  -> 'DOES NOT CONTAIN',
          // 4  -> 'IS ONE OF (SemVer)',
          // 5  -> 'IS NOT ONE OF (SemVer)',
          // 6  -> '< (SemVer)',
          // 7  -> '<= (SemVer)',
          // 8  -> '> (SemVer)',
          // 9  -> '>= (SemVer)',
          // 10 -> '= (Number)',
          // 11 -> '<> (Number)',
          // 12 -> '< (Number)',
          // 13 -> '<= (Number)',
          // 14 -> '> (Number)',
          // 15 -> '>= (Number)',
          // 16 -> 'IS ONE OF (Hashed)',
          // 17 -> 'IS NOT ONE OF (Hashed)'
          "c": "@example.com", // comparison value
          "v": true, // value served when the rule is selected during evaluation
          "i": "bcfb84a7" // variation id (for analytical purposes)
        }
      ]
    }
  }
}

Map

You can set up the SDK to load your feature flag & setting overrides from a map.

map = %{
    "enabledFeature" => true,
    "disabledFeature" => false,
    "intSetting" => 5,
    "doubleSetting" => 3.14,
    "stringSetting" => "test"
}

{ConfigCat, [
    sdk_key: "YOUR SDK KEY",
    flag_overrides: ConfigCat.LocalMapDataSource.new(map, :local_only)
]}

Logging

In the ConfigCat SDK, we use the default Elixir's Logger so you can customise as you like.

Debug level logging helps to inspect how a feature flag was evaluated:

[debug]  Evaluating get_value('isPOCFeatureEnabled').
[debug]  User object: %ConfigCat.User{country: nil, custom: %{}, email: "[email protected]", identifier: "435170f4-8a8b-4b67-a723-505ac7cdea92"}
[debug]  Evaluating rule: [Email:[email protected]] [CONTAINS] [@something.com] => no match
[debug]  Evaluating rule: [Email:[email protected]] [CONTAINS] [@example.com] => match, returning: true

get_all_keys()

You can query the keys from your configuration in the SDK with the get_all_keys() method.

keys = ConfigCat.get_all_keys()

get_all_values()

Evaluates and returns the values of all feature flags and settings. Passing a User Object is optional.

values = ConfigCat.get_all_values(
  ConfigCat.User.new("#UNIQUE-USER-IDENTIFIER#")  # Optional User Object
)

Using ConfigCat behind a proxy

Provide your own network credentials (username/password), and proxy server settings (proxy server/port) by passing the proxy details to the creator method.

{ConfigCat, [
    sdk_key: "YOUR SDK KEY",
    http_proxy: "https://[email protected]:yourproxy.com"
]}

Sample Applications

• Sample App

Look under the hood

• ConfigCat's Elixir SDK on GitHub
• ConfigCat's HexDocs
• ConfigCat's Elixir SDK on Hex.pm