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So I have a bit of a question since I'm having a hard time wrapping my head around it. Currently I have a GraphQL API Server created using Apollo-Server and persisted using a local sqlite database. I have the queries and mutations working correctly.

I also have an external WebSocket server that constantly has messages (that match my GraphQL/Database schema) produced to it at say ws://localhost:8000/websocket. Is it possible to have my GraphQL Server subscribe to that websocket address and constantly parse those messages and use the appropriate mutation to insert into the backend database?

I would then have a Vue frontend that would constantly display the results (via Vue Apollo Clients WS subscription maybe?)

animusdx
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  • I can technically parse that constant stream of data from the WebSocket and constantly call the mutation that will insert into the database. I could then I guess add a PubSub for the Apollo Server as well as the Apollo Client but that ends up being an additional WebSocket server. The original server with the incoming data stream and another WebSocket server for use with Subscriptions to watch for changes? There must be a better way to achieve what I'm imagining? – animusdx Aug 14 '20 at 17:07

2 Answers2

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to have my GraphQL Server subscribe to that websocket address and constantly parse those messages

Typically no, its the other way around - you can make ws server to call graphql server to do the mutations. That is if you want to use WS as the primary transport layer for everything - queries, mutations & subscriptions.

But usually architecture separates queries & mutations because they are more stateless and critical from subscriptions which are more stateful (persisted connection)

client -> queries & mutations -> graphql server --> redis pubsub -+
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client <--> subscriptions <-- graphql subscription server <-------+

(in simpler cases when you don't need high load, you can combine both servers to use in-memory pubsub)

BUT, if you very much want to, ofc you can write custom code to connect graphql server -> listen ws server in the background. See https://github.com/enisdenjo/graphql-ws#node-client for example The problem can appear if you have some user context. You would need to either have custom connection where changes of all users happen. Or have a dedicated connection for every user

Artjom Kurapov
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  • Thanks for this. Apollo documentation was making this a bit confusing. They give an in-memory example, then link to graphql-ws. I couldn't figure out how it all tied in. I think as you said, it makes sense for the websocket to communicate with the GQL server. –  Oct 28 '21 at 23:07
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Yes , it can be done quite easily , just write a service worker or a worker thread that constantly checks for new messages Can be done using worker_threads in node js

And if you need to implement it realtime Make sure your worker thread starts a socket connection and is constantly connected to the port where you are publishing your messages

You can do it using socket.io library

Vicky Yadav
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