README.md

Kubernetes (K8s) ConfigMap support

This package allows you to use ConfigMap objects in Kubernetes to drive the update of dynamic go-flagz at runtime of your service.

Semantics

The Updater is split into two phases:

• Initialize() - used on server startup which allows both static and dynamic flags to be updated from values stored in a ConfigMap
• Start() - kicking off a an fsnotify Go-routine which watches for updates of values in the ConfigMap. To avoid races, this allows only to update dynamic flags.

Code example

// First parse the flags from the command line, as normal.
common.SharedFlagSet.Parse(os.Args[1:])
u, err := configmaps.New(common.SharedFlagSet, "/etc/flagz", logger)
if err != nil {
  logger.Fatalf("failed setting up %v", err)
}
// Read flagz from etcd and update their values in common.SharedFlagSet
if err := u.Initialize(); err != nil {
    log.Fatalf("failed setting up %v", err)
}
// Start listening of ConfigMap updates mounted in /etc/flagz.
u.Start()

In a nutshell

You define a ConfigMap with values for your flags.

kind: ConfigMap
apiVersion: v1
metadata:
  creationTimestamp: 2016-09-09T09:14:38Z
  name: example-config
  namespace: default
data:
  example_my_dynamic_string: something
  example_my_dynamic_int: 20
  example_my_dynamic_json: |-
    {
      "policy": "allow",
      "rate": 50
    }

Then you just push it to your Kubernetes cluster:

# kubectl replace -f example.yaml

And all your jobs referencing this ConfigMap via a volume mount will see updates go-flagz updates to keys in your data. For an end to end example see server_kube.

Caveats

• Kubernetes <= 1.3 validate ConfigMap keys against DNS names, meaning that certain common characters (e.g. _) are not allowed. With >=1.4, ConfigMaps are validated against [-._a-zA-Z0-9]+ RE2 regex.
• With Kubernetes <=1.4 ConfigMaps don't get updated async, but on pod changes and otherwise at least every 60s. See kubernetes#30189.