In a client-server application on the web using sockets, which must come up first?

In a client-server application on the web using sockets, the server must come up first. Here's why:

1. The server is the system that provides resources or services. In the context of web applications, it's the system that hosts the website or application.

2. The client is the system that requests these resources or services. In the context of web applications, it's the user's browser.

3. When using sockets for communication, the server must be up and running first because it needs to create a socket and bind it to a specific address and port. This is known as "listening" for incoming connections.

4. Once the server is listening, clients can then create their own sockets to connect to the server's socket. This is known as "connecting" to the server.

5. If the server is not up and running (i.e., if it's not listening for incoming connections), then clients cannot connect to it. This is why the server must come up first in a client-server application on the web using sockets.