Configmanager

Configmanager is the what mixpanel uses to add dynamic configuration to our code across several services.

Configmanager does these things:

• Reads a file configs.json under a specified path, and watches it for changes
• Interprets the data in the file and gives an easy interface to access the configuration values

Here is a possible example for a hypothetical service called my-service

  cm, err := configmanager.NewClient("/etc/configs", "my-service", fr)
  if err != nil {
  	return err
  }
  defer cm.Close()
  if cm.GetBoolean("my-feature-enabled", false) {
  	// do the my-feature thing
  }

The only requirement for this example to work is placing marshalled configurations in the file /etc/configs/my-service/configs.json

How are configs written

Mixpanel writes configs using JSONNET and they are mounted using kubernetes configmaps. However configmanager only cares about the format and a file that follows the path /dir-path/[name of config group]/configs.json

Two key things you need to unerstand are:

• Config group: A group of configs that belong together in same scope, because they are used by same feature or same service etc
• Config: A key, value pair where value can be an arbitrary JSON and you call configmanager methods specifiying the key

A config group marshalled in a file looks like this:

[
  {
    "key": "feature_enabled_customers",
    "value": {
      "123": {},
      "456": {}
    }
  },
  {
    "key": "scaling_percentage",
    "value": 1
  },
  {
    "key": "timeout_secs",
    "value": 5
  }
]

If such a config is placed in the file /etc/configs/my-configs/configs.json then the configmanager will be constructed using configmanager.NewClient("/etc/configs", "my-configs", fr)