Issue with using keepAlive if set for 20 seconds or more

Question

Having a bit of trouble with keepAlive for Apollo subscriptions. When ever I set a time to seconds or more the listening subscriptions errors out.

{
  "error": "Could not connect to websocket endpoint ws://website.test:8000/graphql. Please check if the endpoint url is correct."
}

Here is ApolloServer setup

const apollo = new ApolloServer({
    introspection: true,
    playground: true,
    typeDefs: schema,
    subscriptions: {
      keepAlive: 40000,
    },
    resolvers,
    context: ........
}

In my local environment when I do not set keepAlive it will stay open indefinitely. If I set it at 10000 works great. With keep alive set at 40000 I get the error and connection closes

UPDATE One thing we just noticed is that this issue happens on the playground but not on our web app. Maybe just a playground thing?

Answer 1

If you check the documentation provided by Apollo GraphQL:

keepAlive - Number

The frequency with which the subscription endpoint should send keep-alive messages to open client connections, in milliseconds, if any.

If this value isn't provided, the subscription endpoint doesn't send keep-alive messages.

As per your provided configuration, with keep alive set at 40000, this is equivalent to 40 seconds. So the subscription endpoint is pinging keep-alive messages every 40 seconds. This probably is too long and the connections is already closed.

You should use a smaller value