What socket data exists within redis?

[y4my4my4m]

I am currently storing data using socket.data.myCustomData and am able to retrieve the data properly between servers.
However, I'm wondering if this data is stored in redis itself?

By that I mean,

• Server 1 -> mySocket.data
• Server 2
• Server 3

If I kill Server 1, will Server 2 and Server 3 be able to access mySocket.data regardless of Server 1 and it's memory/process?

[darrachequesne]

Hi! The socket.data is not persisted to Redis, it only exists in the memory of the 1st server.

That being said, you can totally store it in Redis and fetch it upon connection.

[y4my4my4m]

@darrachequesne By storing/fetching it in Redis do you mean I should manually do a "pub/sub" to redis? Or are there built-in function in the socket.io-redis-adapter to do so?

Feel free to close this issue after your response.
Thank you for everything :)

[darrachequesne]

You can use the fetchSockets() method:

io.on("connection", (socket) => {
  socket.data.someAttribute = 42;
});

// then
const sockets = await io.fetchSockets();
console.log(socket.data.someAttribute); // prints 42

Reference: https://socket.io/docs/v4/server-socket-instance/#socketdata

This also works with a cluster of Socket.IO servers, when using the Redis adapter (or any compatible adapter).

[y4my4my4m]

@darrachequesne

Thank you for your reply.

Unfortunately, I'm confused now.
Didn't you just say the data doesn't persist in redis?

If socket.data.someattribute = 42 only exists in memory on Server1, after killing server1 wouldnt we get something like this:

io.on("connection", (socket) => {
  socket.data.someAttribute = 42;
});

// kill Server1 where the above happened

// then from Server 2
const sockets = await io.fetchSockets();
forEach(s in sockets){
 if(s.data.someAttribute === 42) return true; // this is never triggered
}

I understand that you can fetchSockets and get their content, but that requires getting the in-memory data from each server, correct?
Or do you mean that using fetchSockets will make the data persistent in redis?

[darrachequesne]

but that requires getting the in-memory data from each server

Yes, that's right 👍

In your example above, if server1 gets killed, the data is lost. Sorry for the confusion.

[y4my4my4m]

That clears things up.
Thank you!