Programming Phoenix

The Channel

A Phoenix channel is a conversation. The channel sends messages, receives messages, and keeps state. We call the messages events, and we put the state in a struct called socket.

A Phoenix conversation is about a topic, and it maps onto application concepts like a chat room, a local map, a game, or in our case, the annotations on a video. More than one user might be interested in the same topic at the same time. Channels give you tools to organize your code and the communication among users. The concept that makes channels so powerful in Elixir is that each user’s conversation on a topic has its own isolated, dedicated process.

Here’s the kicker. Whereas request/response interactions are stateless, conversations in a long-running ...