Health checks

Health checks are often used by load balancers to determine if a server is available and ready to start serving traffic. By default, Apollo Server provides a health check endpoint at /.well-known/apollo/server-health which returns a 200 status code if the server has started.

This basic health check may not be comprehensive enough for some applications and depending on individual circumstances, it may be beneficial to provide a more thorough implementation by defining an onHealthCheck function to the ApolloServer constructor options. If defined, this onHealthCheck async function should return if the server is deemed ready or throw if there is an error. Returning (resolving the Promise) will result in an HTTP status code of 200, which is generally desired by most health-check tooling (e.g. Kubernetes, AWS, etc.), while throwing (rejecting the Promise) will result in an HTTP status code of 503.

import { ApolloServer, gql } from 'apollo-server';

// Undefined for brevity.
const typeDefs = gql``;
const resolvers = {};

const server = new ApolloServer({
  typeDefs,
  resolvers,
  async onHealthCheck() {    // Replace the `true` in this conditional with more specific checks!    if (true) {      return;    } else {      throw new Error('...');    }  },});

server.listen().then(({ url }) => {
  console.log(`🚀 Server ready at ${url}`);
  console.log(
    `Try your health check at: ${url}.well-known/apollo/server-health`,
  );
});