Health Check

Yoga is aware of the usefulness of a health check and gives the user maximum possibilities to use the built-in check and create a “readiness” check through a simple plugin.

Types of health checks

There are two types of health checks: liveliness and readiness, they both are a health check but convey a different meaning:

• Liveliness checks whether the service is alive and running
• Readiness checks whether the service is ready to perform work

The difference is that a service can be live but not ready - for example, server has started and is accepting requests (alive), but the read replica it uses is still unavailable (not ready).

A liveliness check is something Yoga can offer out-of-the-box because Yoga is a server and Yoga knows when it’s alive. However, a readiness check is something Yoga cannot figure out on its own, it is a check requiring user-land context.

Having said this, Yoga has a /health route which is used for liveliness check and offers a useReadinessCheck plugin allowing you to implement your own readiness check.

Liveliness

By default, you can check whether Yoga is alive by issuing a request to the /health endpoint and expecting the response 200 OK.

Of course, you can change this endpoint through the healthCheckEndpoint option.

import { createYoga } from 'graphql-yoga'
import { createServer } from 'node:http'
import { schema } from './my-service'
 
const yoga = createYoga({
  schema,
  healthCheckEndpoint: '/live'
})
 
const server = createServer(yoga)
server.listen(4000, () => {
  console.info('Server is running on http://localhost:4000/graphql')
})

A successful response is just 200 OK without a body.

Readiness

Additionally, you might want an endpoint which checks whether the services powering Yoga are ready to perform work.

Since this check requires more context that Yoga cannot assume, you’re recommended to use the core useReadinessPlugin and implement your own check.

import { createYoga, useReadinessCheck } from 'graphql-yoga'
import { createServer } from 'node:http'
import { schema, checkDbAvailable } from './my-service'
 
const yoga = createYoga({
  schema,
  plugins: [
    useReadinessCheck({
      endpoint: '/ready', // default
      check: async () => {
        // if resolves, respond with 200 OK
        // if throw, respond with 503 Service Unavailable and error message as plaintext in body
        await checkDbAvailable()
      }
    })
  ]
})
 
const server = createServer(yoga)
server.listen(4000, () => {
  console.info('Server is running on http://localhost:4000/graphql')
})

Throwing an instance of Error in the check function will have Yoga respond with 503 Service Unavailable with the error’s message in the body.

Alternatively, you can simply return false from the check function to have Yoga respond with just 503 Service Unavailable and no body. This way you can make sure nothing sensitive leaks ever.

import { createYoga, useReadinessCheck } from 'graphql-yoga'
import { createServer } from 'node:http'
import { schema, checkDbAvailable } from './my-service'
 
const yoga = createYoga({
  schema,
  plugins: [
    useReadinessCheck({
      endpoint: '/ready', // default
      check: async () => {
        try {
          await checkDbAvailable()
          // if true, respond with 200 OK
          return false
        } catch (err) {
          // log the error on the server for debugging purposes
          console.error(err)
          // if false, respond with 503 Service Unavailable and no bdy
          return false
        }
      }
    })
  ]
})
 
const server = createServer(yoga)
server.listen(4000, () => {
  console.info('Server is running on http://localhost:4000/graphql')
})