Chapter 4. Example application using a fallback function with the circuit breaker add-on

You can use the fallback method of the circuit breaker object to add your defined fallback function to the circuit breaker. If the call to the remote service fails after the circuit breaker fire method is executed, the fallback function is then called automatically.

For more information about the fallback method and other member types that you can use with the circuit breaker add-on, see the Circuit Breaker Add-on 5.0.0 API Documentation.

This example is based on the greeting-service that sends calls to the remote name-service that might fail. This example shows how to define a fallback function that prints the following message to the web console: This is the fallback function.

...

// Import the circuit breaker add-on
const Opossum = require('@redhat/opossum');

...

// Create a new circuit breaker instance and pass the
// remote nameService as its first parameter
const circuit = new Opossum(nameService, circuitOptions);

// Define a fallback function that will be called when
// the remote nameService fails
function fallback(result) {
    console.log('This is the fallback function', result);
}

// Use the circuit breaker's fallback method to add the
// fallback function to the circuit breaker instance
circuit.fallback(fallback);

...

// Greeting API
app.get('/api/greeting', (request, response) => {
  // Use the circuit breaker’s fire method to execute the call
  // to the name service
  circuit.fire(`${nameServiceHost}/api/name`).then(name => {
    response.send({ content: `Hello, ${name}`, time: new Date() });
  }).catch(console.error);
});

...