@loopback/health

@loopback/health

This module contains a component to report health status using @cloudnative/health.

Installation

npm install --save @loopback/health

Basic use

The component should be loaded in the constructor of your custom Application class.

Start by importing the component class:

import {HealthComponent} from '@loopback/health';

In the constructor, add the component to your application:

this.component(HealthComponent);

By default, three routes are exposed at:

• /health - overall health status
• /live - liveness status
• /ready - readiness status

The paths can be customized via Health configuration as follows:

this.configure(HealthBindings.COMPONENT).to({
  healthPath: '/health',
  livePath: '/live',
  readyPath: '/ready',
});

{% include note.html content="this.configure() must be called before this.component() to take effect. This is a known limitation ." %}

http://localhost:3000/health returns health in JSON format, such as:

{
  "status": "UP",
  "checks": [
    {"name": "readiness", "state": "UP", "data": {"reason": ""}},
    {"name": "liveness", "state": "UP", "data": {"reason": ""}}
  ]
}

It also has to be noted, that by default the OpenAPI spec is disabled and therefore the endpoints will not be visible in the API explorer. The spec can be enabled by setting openApiSpec to true.

this.configure(HealthBindings.COMPONENT).to({
  openApiSpec: true,
});

Add custom live and ready checks

The health component allows extra live and ready checks to be added.

Liveness probes are used to know when to restart a container. For example, in case of a deadlock due to a multi-threading defect which might not crash the container but keep the application unresponsive. A custom liveness probe would detect this failure and restart the container.

Readiness probes are used to decide when the container is available for accepting traffic. It is important to note, that readiness probes are periodically checked and not only at startup.

Important: It is recommended to avoid checking dependencies in liveness probes. Liveness probes should be inexpensive and have response times with minimal variance.

import {LiveCheck, ReadyCheck, HealthTags} from '@loopback/health';

const myLiveCheck: LiveCheck = () => {
  return Promise.resolve();
};
app.bind('health.MyLiveCheck').to(myLiveCheck).tag(HealthTags.LIVE_CHECK);

// Define a provider to check the health of a datasource
class DBHealthCheckProvider implements Provider<ReadyCheck> {
  constructor(@inject('datasources.db') private ds: DataSource) {}

  value() {
    return () => this.ds.ping();
  }
}

app
  .bind('health.MyDBCheck')
  .toProvider(DBHealthCheckProvider)
  .tag(HealthTags.READY_CHECK);

const myReadyCheck: ReadyCheck = () => {
  return Promise.resolve();
};
app.bind('health.MyReadyCheck').to(myReadyCheck).tag(HealthTags.READY_CHECK);

Contributions

• Guidelines
• Join the team

Tests

Run npm test from the root folder.

Contributors

See all contributors.

License

MIT