边缘函数触发器与请求生命周期
了解边缘函数在请求生命周期的哪个环节接入，以及哪些触发点可以让您在边缘修改请求和响应。
边缘函数触发器与请求生命周期 是 CoddyKit 上的免费 Caching Strategies: Redis + CDN + Edge Computing 课时。 这是第 4 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 Caching Strategies: Redis + CDN + Edge Computing 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Caching Strategies: Redis + CDN + Edge Computing 课程共包含 4 节课。
本课时的部分内容尚未翻译，以英文显示。
The Edge Request Lifecycle
When a request reaches a CDN edge, it passes through distinct phases. Edge functions can attach to specific phases to inspect or transform the request and response.
- Viewer request: as the request arrives
- Origin request: before fetching from origin
- Origin response: after origin replies
- Viewer response: before returning to the user
Viewer Request Trigger
The viewer request trigger runs on every incoming request, even cache hits. Use it for lightweight logic like redirects, header normalization, or A/B routing.
Origin Request Trigger
The origin request trigger runs only on cache misses, just before the edge contacts the origin. It is ideal for rewriting the origin path or choosing a different backend.
function handler(event) {
var req = event.request;
req.uri = "/v2" + req.uri;
return req;
}Origin Response Trigger
The origin response trigger fires after the origin replies but before the response is cached. Use it to adjust cache headers or inject security headers.
Viewer Response Trigger
The viewer response trigger runs before the response goes to the user, on both hits and misses. Use it for final header tweaks like adding CORS or HSTS.
function handler(event) {
var res = event.response;
res.headers["x-edge"] = { value: "true" };
return res;
}Triggers and the Cache
Knowing which triggers run on cache hits matters for performance and cost. Viewer triggers run every time; origin triggers run only on misses. Put heavy logic on origin triggers to avoid paying for it on every hit.
Short-Circuiting a Request
An edge function can return a response directly instead of forwarding it, short-circuiting the lifecycle. This is great for maintenance pages, auth gates, or geo-blocks.
function handler(event) {
var country = event.request.headers["cloudfront-viewer-country"];
if (country && country.value === "XX") {
return { statusCode: 403, body: "Blocked" };
}
return event.request;
}Modifying Requests vs Responses
Request triggers can change the URI, headers, and query string before routing. Response triggers can change status codes and headers. Choose the trigger that matches what you need to mutate.
Performance Constraints
Edge functions run inside tight limits on CPU time and memory because they execute on every request at scale. Keep them small, avoid network calls in viewer triggers, and prefer synchronous logic.
- Tiny scripts equal predictable latency
- Heavy logic belongs on origin triggers or full edge runtimes
Choosing the Right Trigger
A quick decision guide:
- Redirect or auth gate: viewer request
- Rewrite origin path: origin request
- Adjust cache TTL: origin response
- Add response headers for everyone: viewer response
Debugging Lifecycle Triggers
Test each trigger in isolation. Log the phase and inspect headers added by the CDN (like the viewer country) to confirm your function runs where you expect.
Quick Check
Confirm your understanding of edge trigger points.
Recap
You learned the four edge function trigger points across the request lifecycle: viewer request, origin request, origin response, and viewer response. You saw which run on cache hits versus misses, how to short-circuit a request, and how to pick the right trigger while respecting edge runtime limits.
常见问题解答
「边缘函数触发器与请求生命周期」课时是免费的吗？
是的 — 「边缘函数触发器与请求生命周期」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Caching Strategies: Redis + CDN + Edge Computing 课程的其余内容，请升级到 CoddyKit PRO。 Caching Strategies: Redis + CDN + Edge Computing 课程共包含 4 节课。
「边缘函数触发器与请求生命周期」这节课中我会学到什么？
了解边缘函数在请求生命周期的哪个环节接入，以及哪些触发点可以让您在边缘修改请求和响应。 你通过在浏览器中直接运行的动手代码来练习 Caching Strategies: Redis + CDN + Edge Computing，全天候 AI 导师会在你学习这节课的过程中回答你的问题。
学习 Caching Strategies: Redis + CDN + Edge Computing 需要有经验吗？
无需任何先前经验。CoddyKit 上的 Caching Strategies: Redis + CDN + Edge Computing 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 4 节课，共 4 节。
「边缘函数触发器与请求生命周期」课时需要多长时间？
大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。
我能在这节 Caching Strategies: Redis + CDN + Edge Computing 课中编写并运行代码吗？
能。每节 Caching Strategies: Redis + CDN + Edge Computing 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。