Trait Service

pub trait Service {
    type Config: DeserializeOwned;

    // Provided methods
    fn on_config_change(
        &mut self,
        ctx: &PicoContext,
        new_config: Self::Config,
        old_config: Self::Config,
    ) -> CallbackResult<()> { ... }
    fn on_start(
        &mut self,
        context: &PicoContext,
        config: Self::Config,
    ) -> CallbackResult<()> { ... }
    fn on_stop(&mut self, context: &PicoContext) -> CallbackResult<()> { ... }
    fn on_leader_change(&mut self, context: &PicoContext) -> CallbackResult<()> { ... }
    fn on_health_check(&self, context: &PicoContext) -> CallbackResult<()> { ... }
}

Service trait. Implement it in your code to create a service.

Required Associated Types

type Config: DeserializeOwned

Use this associated type to define configuration of your service.

Provided Methods

fn on_config_change( &mut self, ctx: &PicoContext, new_config: Self::Config, old_config: Self::Config, ) -> CallbackResult<()>

Callback to handle service configuration change once instance receives it.

Idempotency

WARNING This callback may be called several times in a row. It is the responsibility of the plugin author to make this function idempotent.

Poison

Return an error here to poison current instance. This will not cancel reconfiguration process, but will mark instance as unavailable for rpc messaging.

Instance can be “healed” if any of on_leader_change or on_config_change callbacks in the future return Ok.

Arguments

• ctx: instance context
• new_config: new configuration
• old_config: previous defined configuration

fn on_start( &mut self, context: &PicoContext, config: Self::Config, ) -> CallbackResult<()>

Called at service start on every instance.

Idempotency

WARNING This callback may be called several times in a row (without any calls to Self::on_stop). It is the responsibility of the plugin author to make this function idempotent.

An error returned here abort plugin load clusterwide thus forcing on_stop callback execution on every instance.

Arguments

• context: instance context
• config: initial configuration

fn on_stop(&mut self, context: &PicoContext) -> CallbackResult<()>

Called on instance shutdown, plugin removal or failure of the initial load. Returned error will only be logged causing no effects on plugin lifecycle.

Idempotency

WARNING This callback may be called several times in a row. It is the responsibility of the plugin author to make this function idempotent.

Arguments

• context: instance context

fn on_leader_change(&mut self, context: &PicoContext) -> CallbackResult<()>

Called when replicaset leader is changed. This callback will be called exactly on two instances - the old leader and the new one.

Idempotency

WARNING This callback may be called several times in a row. It is the responsibility of the plugin author to make this function idempotent.

Poison

Return an error here to poison current instance. This will not cancel reconfiguration process, but will mark instance as unavailable for rpc messaging.

Instance can be “healed” if any of on_leader_change or on_config_change callbacks in the future return Ok.

Arguments

• context: instance context

fn on_health_check(&self, context: &PicoContext) -> CallbackResult<()>

on_healthcheck is a callback that should be called to determine if the service is functioning properly On an error instance will be poisoned

Unimplemented

WARNING This feature is not yet implemented. The callback is never called. TODO.

Implementors