Election

How can you start a standalone service in the backend using VonaJS?

Since VonaJS uses a distributed architecture, multiple Workers can be started in the backend. So, on which Worker should the standalone service be started?

VonaJS provides Election for this scenario, which works as follows:

1. All Workers compete to acquire ownership
2. You can specify the number of Workers that can acquire ownership simultaneously
3. The Worker that acquires ownership can start the service
4. If a Worker that owns ownership exits normally or terminates abnormally, other Workers will continue to compete for ownership

Create meta.election

For example, create meta.election in the module demo-student. Start a timer in the selected Worker to output Hello World every 2 seconds.

1. Cli Command

$ vona :create:bean meta election --module=demo-student

2. Menu Command

TIP

Context menu - [Module Path]: Vona Meta/Election

meta.election Definition

export type TypeElectionObtainResource = 'echo';

@Meta()
export class MetaElection extends BeanElectionBase<TypeElectionObtainResource> {}

• TypeElectionObtainResource: Defines the type of Election resource

Create Module Monkey

Next, create a Module Monkey that responds to the appStarted and appClose hooks.

• See also: App Startup Customization

export class Monkey extends BeanSimple implements IMonkeyAppStarted {
  async appStarted() {
    const scope = this.app.scope(__ThisModule__);
    scope.election.obtain(
      'echo',
      () => {
        // custom logic
      },
      async () => {
        // cleanup
      },
    );
  }
}

• appStarted: Calls election.obtain to acquire ownership of the specified resource. A callback function is invoked upon acquisition of ownership

Tickets

When calling election.obtain, you can specify that multiple Workers are allowed to acquire ownership:

async appStarted() {
  const scope = this.app.scope(__ThisModule__);
  scope.election.obtain('echo', () => {
    // custom logic
  }, async () => {
    // cleanup
+ }, { tickets: 2 });
}

Name	Description
tickets	Allows a specified number of Workers to acquire ownership. Defaults to 1