activation

Activation-aware retry logic for cold-start tolerance.

When KEDA scales an agent to 0 replicas, the first request may encounter:

503 Service Unavailable (interceptor buffering, no backend yet)
Connection refused (pod not started)
504 Gateway Timeout (cold start exceeded upstream timeout)

This module provides configurable retry with exponential backoff and jitter to handle these transient failures transparently.

Usage

Use [Client::call_with_activation] for activation-aware A2A calls, or [retry_with_activation] for generic retry over any async callable.

Structs

`ActivationConfig`

Configuration for activation-aware retries when calling potentially cold agents.

These values drive the SDK-side retry budget. The KEDA HTTP Add-on HTTPScaledObject does NOT have a CRD-level queueDepth — this is the platform’s enforcement layer.

Fields

Field	Type	Description
`max_cold_start_timeout`	`Duration`	Max time to wait for a cold agent to respond. Default: 5s.
`initial_backoff`	`Duration`	Initial retry delay. Default: 100ms.
`max_backoff`	`Duration`	Max retry delay cap. Default: 2s.
`max_retries`	`u32`	Max retries before giving up. Default: 3.
`jitter`	`bool`	Add jitter to backoff. Default: true.

Methods

`backoff_for_attempt`

fn backoff_for_attempt(&self, attempt: u32) -> Duration

Compute the backoff duration for a given attempt (0-indexed).

Uses exponential backoff: initial * 2^attempt, capped at max_backoff. When jitter is enabled, the result is multiplied by a factor in [0.5, 1.0].

`is_retriable_status`

fn is_retriable_status(status: u16) -> bool

Check if an HTTP status code indicates a retriable cold-start scenario.

`is_retriable_error`

fn is_retriable_error(error_msg: &str) -> bool

Check if an error message indicates a retriable connection failure.

Functions

`idempotency_key`

fn idempotency_key(request_id: &str, attempt: u32) -> String

Generate an idempotency key for safe retries on state-mutating requests.

Format: {request_id}:{attempt} — the server should deduplicate by this key.

`activation_delay`

async fn activation_delay(duration: Duration)

Async delay for activation retries. Uses tokio::time::sleep on native and std::thread::sleep (WASI monotonic clock) on WASM.

`retry_with_activation`

async fn retry_with_activation<T, E, F, Fut>(config: &ActivationConfig, call_fn: F) -> Result<T, E>
where
    E: Display,
    F: FnMut,
    Fut: Future

Execute an async operation with activation-aware retries.

call_fn receives the 0-indexed attempt number and returns Result<T, E>. Errors whose Display output matches [ActivationConfig::is_retriable_error] are retried with exponential backoff; all other errors are returned immediately.

Returns the first Ok, or the last Err when retries are exhausted.