Health checks

Load balancers often use health checks to determine if a server is available and ready to serve traffic.

GraphQL-level health checks

The easiest way to determine if your GraphQL server is healthy is to run a GraphQL operation.

Every GraphQL server supports a trivial query that requests the __typename of the top-level Query type. This means every GraphQL server can respond to a GET request to a URL such as:

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https://your.server/graphql?query=%7B__typename%7D

Note that this health check will run an actual GraphQL operation. If your server requires special headers or cookies to run any query, you'll need to provide those with your request.

If you want to create a health check for your HTTP server that is unrelated to the health of the GraphQL execution engine (i.e., such as Apollo Server 3's health check feature), you can add a GET handler that always succeeds to your web framework.

Below is an example of an HTTP server health check with expressMiddleware:

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// imports, etc.
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const app = express();
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const server = new ApolloServer({
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  typeDefs,
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  resolvers,
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});
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await server.start();
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app.use('/graphql', cors<cors.CorsRequest>(), express.json(), expressMiddleware(server));
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await new Promise<void>((resolve) => app.listen({ port: 4000 }, resolve));
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// Our GraphQL server is listening for GraphQL operations
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// on `http://localhost:4000/graphql`
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console.log(`🚀 Server ready at http://localhost:4000/graphql`);
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// Requests to `http://localhost:4000/health` now return "Okay!"
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app.get('/health', (req, res) => {
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  res.status(200).send('Okay!');
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});

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// imports, etc.
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const app = express();
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const server = new ApolloServer({
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  typeDefs,
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  resolvers,
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});
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await server.start();
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app.use('/graphql', cors(), express.json(), expressMiddleware(server));
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await new Promise((resolve) => app.listen({ port: 4000 }, resolve));
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// Our GraphQL server is listening for GraphQL operations
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// on `http://localhost:4000/graphql`
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console.log(`🚀 Server ready at http://localhost:4000/graphql`);
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// Requests to `http://localhost:4000/health` now return "Okay!"
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app.get('/health', (req, res) => {
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  res.status(200).send('Okay!');
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});