Compute Server

Abstract

---

• Server that handles the business logic of the system like Authentication

Stateful Compute Server

---

• Remembers client data like Session-Cookie Authentication (state) from one request to the next
• From the above diagram, user A’s session data and profile image are stored in Server 1
• To authenticate User A, HTTP requests must be routed to Server 1
• If a request is sent to other servers like Server 2, authentication would fail because Server 2 does not contain User A’s session data
• Similarly, all HTTP requests from User B must be routed to Server 2; all requests from User C must be sent to Server 3

Limitations

• Every request from the same client must be routed to the same server. This can be done with Sticky Session with an overhead
• Adding and removing servers is much difficult with this approach, challenging to handle server failures
• Thus, less Scalability (可扩展性) and Fault Tolerance (容错性)

Stateless Compute Server

---

• Move the state li Session-Cookie Authentication out of the Compute Server, and store them in an external Database. And all the compute servers fetch state data from a shared database
• Requests from Client can be sent to any compute servers, resolves the limitations of stateful compute server
• Thus more Scalability (可扩展性) and Fault Tolerance (容错性)