Trait Strategy 

pub trait Strategy: Send + Sync {
    // Required method
    fn desired_replicas(
        &self,
        state: &ClusterState,
        signals: &LiveSignals,
        config: &ConfigSignals,
        now: Timestamp,
    ) -> Vec<DesiredReplica>;

    // Provided methods
    fn signal_request(
        &self,
        _state: &ClusterState,
        _config: &ConfigSignals,
    ) -> SignalRequest { ... }
    fn update_state(
        &self,
        _state: &ClusterState,
        _signals: &LiveSignals,
        _config: &ConfigSignals,
        _now: Timestamp,
    ) -> StateWrite { ... }
}

One cluster-autoscaling strategy: a pair of pure functions the controller runs each tick. See the module docs.

Send + Sync so the controller (which holds a set of boxed strategies) can run on its own task.

Required Methods

fn desired_replicas( &self, state: &ClusterState, signals: &LiveSignals, config: &ConfigSignals, now: Timestamp, ) -> Vec<DesiredReplica>

The replica slots this strategy contributes to state’s desired set at time now.

Provided Methods

fn signal_request( &self, _state: &ClusterState, _config: &ConfigSignals, ) -> SignalRequest

The live signals this strategy needs to evaluate state this tick, declared as a pure function of the durable state and the tick’s config signals. The kernel unions the requests across strategies, fetches them through the ctx, and passes the result to Strategy::update_state and Strategy::desired_replicas. The default requests nothing, which suits a strategy that works off durable state alone (like the baseline).

fn update_state( &self, _state: &ClusterState, _signals: &LiveSignals, _config: &ConfigSignals, _now: Timestamp, ) -> StateWrite

The durable writes this strategy wants for state at time now. The default is no write, which suits a strategy that only ever contributes replicas (like the baseline). An empty StateWrite means “write nothing”: the kernel drops it without emitting a decision.

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors

impl Strategy for BaselineStrategy

impl Strategy for GracefulReconfigurationStrategy

impl Strategy for HydrationBurstStrategy

impl Strategy for OnRefreshStrategy