Node.js Cloud Events Function

Welcome to your new Node.js function project! The boilerplate function code can be found in index.js. This function is meant to respond to Cloud Events.

Local execution

After executing npm install, you can run this function locally by executing npm run local.

The runtime will expose three endpoints.

• / The endpoint for your function.
• /health/readiness The endpoint for a readiness health check
• /health/liveness The endpoint for a liveness health check

The health checks can be accessed in your browser at http://localhost:8080/health/readiness and http://localhost:8080/health/liveness. You can use curl to POST an event to the function endpoint:

curl -X POST -d '{"name": "Tiger", "customerId": "0123456789"}' \
  -H'Content-type: application/json' \
  -H'Ce-id: 1' \
  -H'Ce-source: cloud-event-example' \
  -H'Ce-type: dev.knative.example' \
  -H'Ce-specversion: 1.0' \
  http://localhost:8080

The readiness and liveness endpoints use overload-protection and will respond with HTTP 503 Service Unavailable with a Client-Retry header if your function is determined to be overloaded, based on the memory usage and event loop delay.

The Function Interface

The index.js file may export a single function or a Function object. The Function object allows developers to add lifecycle hooks for initialization and shutdown, as well as providing a way to implement custom health checks.

The Function interface is defined as:

export interface Function {
  // The initialization function, called before the server is started
  // This function is optional and should be synchronous.
  init?: () => any;

  // The shutdown function, called after the server is stopped
  // This function is optional and should be synchronous.
  shutdown?: () => any;

  // The liveness function, called to check if the server is alive
  // This function is optional and should return 200/OK if the server is alive.
  liveness?: HealthCheck;

  // The readiness function, called to check if the server is ready to accept requests
  // This function is optional and should return 200/OK if the server is ready.
  readiness?: HealthCheck;

  logLevel?: LogLevel;

  // The function to handle HTTP requests
  handle: CloudEventFunction | HTTPFunction;
}

Handle Signature

CloudEvent functions are used in environments where the incoming HTTP request is a CloudEvent. The function signature is:

interface CloudEventFunction {
  (context: Context, event: CloudEvent): CloudEventFunctionReturn;
}

Where the return type is defined as:

type CloudEventFunctionReturn = Promise<CloudEvent> | CloudEvent | HTTPFunctionReturn;
type HTTPFunctionReturn = Promise<StructuredReturn> | StructuredReturn | ResponseBody | void;

The function return type can be anything that a simple HTTP function can return or a CloudEvent. Whatever is returned, it will be sent back to the caller as a response.

Where the StructuredReturn is a JavaScript object with the following properties:

interface StructuredReturn {
  statusCode?: number;
  headers?: Record<string, string>;
  body?: ResponseBody;
}

If the function returns a StructuredReturn object, then the statusCode and headers properties are used to construct the HTTP response. If the body property is present, it is used as the response body. If the function returns void or undefined, then the response body is empty.

The ResponseBody is either a string, a JavaScript object, or a Buffer. JavaScript objects will be serialized as JSON. Buffers will be sent as binary data.

Health Checks

The Function interface also allows for the addition of a liveness and readiness function. These functions are used to implement health checks for the function. The liveness function is called to check if the function is alive. The readiness function is called to check if the function is ready to accept requests. If either of these functions returns a non-200 status code, then the function is considered unhealthy.

A health check function is defined as:

/**
 * The HealthCheck interface describes a health check function,
 * including the optional path to which it should be bound.
 */
export interface HealthCheck {
  (request: Http2ServerRequest, reply: Http2ServerResponse): any;
  path?: string;
}

By default, the health checks are bound to the /health/liveness and /health/readiness paths. You can override this by setting the path property on the HealthCheck object, or by setting the LIVENESS_URL and READINESS_URL environment variables.

Testing

This function project includes a unit test and an integration test. All .js files in the test directory are run.

npm test