Holds the k8s readiness-probe status and enforces a drain window on shutdown.

On SIGTERM, OTP walks the supervision tree in reverse start order and terminates children in reverse order. This GenServer must be the last child of your application supervisor so it terminates first. Its terminate/2 flips the /probe/readiness probe to 503 via :persistent_term and sleeps for the drain window, giving Kubernetes time to stop routing traffic and allowing in-flight requests to finish before other resources (Repo, Endpoint, etc.) are torn down.

Usage

# lib/my_app/application.ex — last entry in children
children = [
  MyApp.Repo,
  MyAppWeb.Endpoint,
  {KubernetesProbes.Drainer, otp_app: :my_app}
]

Configuration

# config/config.exs — production default
config :my_app, KubernetesProbes.Drainer, wait: 20_000

# config/dev.exs — avoid 20s hang on Ctrl-C
config :my_app, KubernetesProbes.Drainer, wait: 100

# config/test.exs — avoid slow suite teardown
config :my_app, KubernetesProbes.Drainer, wait: 10

Options

• :otp_app — the OTP application to read configuration from (required).
• :wait — drain window in milliseconds. Can be set via config (see above) or passed directly to override config: {KubernetesProbes.Drainer, otp_app: :my_app, wait: 5_000}. Defaults to 20_000.