How does browsers handle DNS lookup and TLS with WebSockets?
I'm currently considering the option of implementing websockets in my application. But before doing so, I want to make sure I understand correctly how it works and if it's gonna be worth it.
I understand the basics: Via WebSockets the handshake will be made only once via HTTP and then will talk to the server in order to switch to a lower level TCP layer, at that point, we have a full-duplex channel between the server and the client.
Currently I'm measuring the ajax requests made to my server (which are many), I've got this information:
The "DNS Lookup", "Initial connection" and "SSL" times are what I'm trying to eliminate (if possible)
For my understanding these times are part of the handshaking process and I'm assuming that using websockets it will happen only on the beginning (the handshake), but I'm not sure.
So my question is: Am I correct? Implementing WebSockets will ensure that the "DNS lookup" and the "Initial connection" steps happen only on the handshake?
Thanks in advance for your help, and sorry if my understanding is wrong.
I understand the basics: Via WebSockets the handshake will be made only once via HTTP and then will talk to the server in order to switch to a lower level TCP layer, at that point, we have a full-duplex channel between the server and the client.
It will not switch to a lower level TCP layer. Instead it will switch the protocol from plain HTTP (request, response) to a message based protocol - which like HTTP is on top of TCP at the application layer and not at a lower level. It's just a different protocol on the same level. It behaves a bit like TCP in that you can send and receive messages at any time without being restricted to request/response scheme of HTTP. But for example TCP is a data stream while WebSockets implements a message oriented protocol.
And, DNS is outside of WebSockets. DNS is only needed to lookup the IP address to establish the TCP connection which then gets used to do the initial HTTP handshake which is needed before the protocol switch to WebSockets.
The situation is similar with TLS. After the DNS lookup to get the IP address the TCP connection is established, then the TLS session on top of the TCP connection is established and then the initial HTTP handshake preceding the switch to WebSockets is done: ie HTTP inside a TLS tunnel inside a TCP connection - in other words HTTPS. The WebSocket protocol is then also spoken inside this TLS tunnel, similar how it is done with HTTP.
So my question is: Am I correct? Implementing WebSockets will ensure that the "DNS lookup" and the "Initial connection" steps happen only on the handshake?
Correct. At the beginning of each ws:// connection you might have a DNS lookup if the IP for the name is not already cached. You will have a TCP handshake and you will have a HTTP handshake which then leads to the protocol switch. This is true for every ws:// connection. And for wss:// there is additionally the creation of the TLS tunnel after the TCP connection was established and before the HTTP handshake gets started.
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