PUSH Technologies - An Overview
PUSH technologies allow servers to deliver updates to clients the moment something meaningful happens. Unlike traditional request/response patterns, PUSH reverses the flow: the server becomes the initiator.
This article provides a clear architectural overview of the major PUSH mechanisms, how they behave, where they fit, and how to choose between them. Deep‑dive technical articles for each protocol are linked throughout.
Why PUSH Matters
Modern systems increasingly expect events to arrive instantly. Users no longer tolerate:
- polling delays
- stale dashboards
- race conditions between systems
- manual refresh cycles
PUSH solves these challenges by establishing:
- a persistent or semi‑persistent communication channel
- a subscription or routing mechanism
- an event‑triggered delivery engine
PUSH enables:
- real‑time dashboards
- collaborative experiences
- workflow updates
- IoT telemetry
- notification ecosystems
- cross‑system synchronisation
The Major PUSH Technologies
This overview covers the six primary PUSH families used across web, mobile, and IoT systems:
- Server‑Sent Events (SSE) — one‑way server → client streaming
- WebSockets — full‑duplex, bidirectional communication
- MQTT v5 — IoT‑focused publish/subscribe messaging
- Long‑Polling — legacy, simulated PUSH using held HTTP requests
- Web Push API — browser notifications delivered via Service Workers
- Web Push Protocol (RFC 8030) — server → push service → browser channel
Each solves a different architectural problem. None replaces the others.
Summary Comparison Table
| Technology | Directionality | Ideal Use Cases | Complexity |
|---|---|---|---|
| SSE | Server → Client | Notifications, dashboards, workflow events | Low |
| WebSockets | Full‑duplex | Chat, collaboration, presence, shared editing | Medium–High |
| MQTT v5 | Publish/Subscribe | IoT, telemetry, distributed systems | Medium |
| Long‑Polling | Simulated PUSH | Legacy fallback, older browsers/servers | Low |
| Web Push API | Server → Browser (via SW) | Notifications when app is closed | Medium |
| Web Push Protocol (RFC 8030) | Server → Push Service → Browser | Reliable background delivery | Medium |
The Universal PUSH Lifecycle
Regardless of the technology, PUSH systems follow a similar sequence:
- Intent / Discovery
The client declares interest (“I want updates for X.”)
- Channel Establishment
A connection or subscription pipeline is created.
- Subscription Registration
The server/broker maps the client to topics, routes, or events.
- Delivery
Events are pushed without polling.
Technologies differ only in how they perform these steps.
When to Use Which Technology
- Use SSE when you need simple, reliable one‑way streaming over HTTP.
- Use WebSockets when both sides must send events at any time.
- Use MQTT when you need scalable pub/sub or IoT‑style routing.
- Use Long‑Polling for maximum compatibility with legacy environments.
- Use the Web Push API for system‑level browser notifications.
- Use the Web Push Protocol when communicating with push services.
High‑Level Architectural Considerations
Scalability
- SSE and WebSockets require persistent connections at scale.
- MQTT brokers handle very large fan‑out and dynamic topic routing.
- Web Push offloads scaling to the browser vendor’s push service.
Security
- All modern PUSH channels require TLS.
- Web Push enforces encrypted payloads even after leaving your server.
- MQTT requires careful ACL and topic‑level access design.
Backwards Compatibility
- Long‑Polling remains the universal fallback.
- SSE degrades to long‑polling in some environments.
- WebSockets require explicit upgrade support.
Operational Lifecycle
- WebSockets require heartbeat handling.
- MQTT requires broker management and topic governance.
- Web Push requires subscription renewal logic.
Linked Deep‑Dive Articles
For full technical detail, see the following dedicated articles:
- PUSH: Server‑Sent Events (SSE)
- PUSH: WebSockets
- PUSH: MQTT v5
- PUSH: Long‑Polling
- PUSH: Web Push API
- PUSH: Web Push Protocol (RFC 8030)
Each sub‑article includes:
- protocol flows
- wire‑level behaviour
- lifecycle diagrams
- example frames/messages
- deployment considerations
- common pitfalls and diagnostics
