README
@loopback/health
This module contains a component to report health status using @cloudnative/health.
Installation
npm install --save @loopback/health
Basic use
{% include note.html content="this.configure() must be called before this.component() to take effect. This is a known limitation." %}
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',
});
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,
});
live
and ready
checks
Add custom 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
Tests
Run npm test
from the root folder.
Contributors
See all contributors.
License
MIT