Selecting between bidirectional connections and unidirectional streams isn't just a technology preference; it's a fundamental trade-off in system topology and resource cost.

What We're Building

We are designing a notification endpoint for a microservice mesh. This service ingests telemetry data from distributed sensors and pushes critical alerts to frontend clients. The architecture must support millions of concurrent connections without exhausting server memory. We evaluate the trade-off between bidirectional WebSockets and unidirectional Server-Sent Events to determine which fits this use case.

Step 1 — Define Directionality

The first decision involves data flow. WebSockets require two-way communication for full-duplex traffic, while Server-Sent Events (SSE) are strictly server-to-client. If your frontend only needs to receive updates, SSE is lighter.…