What is the Journey of a Slack Message?

In a recent technical article, Slack explains how its real-time messaging framework works. Here is my short summary:

A Slack message travels through five important servers:

• WebApp: defines the API that a Slack client could use

• Admin Server (AS): finds the correct Channel Server using channel ID

• Channel Server (CS): maintains the history of message channel

• Gateway Server (GS): deployed in each geographic region. Maintain WebSocket channel subscription

• Envoy: service proxy for cloud-native applications

• Because there are too many channels, the Channel Server (CS) uses consistent hashing to allocate millions of channels to many channel servers.

• Slack messages are delivered through WebApp and Admin Server to the correct Channel Server.

• Through Gate Server and Envoy (a proxy), the Channel Server will push messages to message receivers.

• Message receivers use WebSocket, which is a bi-directional messaging mechanism, so they are able to receive updates in real-time.