Day 22: WebSockets vs SSE vs gRPC; NAT, CIDR, subnets
When request/response isn't enough
Plain HTTP is request-then-response — the server can't push data to the client unprompted. Three patterns fill that gap, each suited to a different shape of problem.
- WebSockets — a full-duplex, persistent connection; either side can send at any time. Best for bidirectional, high-frequency traffic (chat, live collaboration, gaming).
- SSE (Server-Sent Events) — a simple one-way stream from server to client over plain HTTP. Best when only the server needs to push (live notifications, progress updates) and you want something simpler than WebSockets.
- gRPC — a strongly-typed RPC framework over HTTP/2, with streaming support in both directions. Best for service-to-service communication where you want a strict contract (via Protobuf) and top-tier performance.
Pick the least powerful tool that fits
SSE is simpler to operate (it's just HTTP — works through most proxies/load balancers with zero special handling) and is the right choice whenever the client never needs to push data back. Reach for WebSockets only when you genuinely need bidirectional, low-latency traffic.
NAT, CIDR, and subnets
NAT (Network Address Translation) lets many devices on a private network share one public IP address — your home router rewrites outgoing packets' source address to its own public IP, and remembers how to route replies back to the right internal device.
CIDR notation (10.0.0.0/16) describes an IP range: the number after the slash is how many leading bits are fixed as the network prefix, leaving the rest for host addresses. A /24 gives you 256 addresses; a /16 gives you 65,536. Subnetting is dividing a larger network into smaller ones — exactly what you'll do deliberately when designing a VPC in Phase 20.
Key terms
- WebSocket
- A persistent, full-duplex connection allowing either side to send data at any time.
- SSE
- A one-way, server-to-client streaming pattern built on plain HTTP.
- NAT
- Rewriting private IP addresses to a shared public IP so multiple devices can share one address for outbound traffic.
- CIDR
- Notation (e.g. /24) describing an IP range by how many bits are fixed as the network prefix.
You need to push live progress updates to a browser, one-directionally, with minimal operational complexity. What's the best fit?
