The ZEIT Smart CDN is active for all deployments and domains on your account and caches your content at the edge to serve data to your users as fast as possible.
The Smart CDN is available for both the Free and Unlimited plans and can be activated for Serverless Functions by providing Cache-Control
headers.
If Cache-Control
headers are provided all dynamic responses from Serverless Functions will be cached in all regions.
What is Cached?
Responses with a HTTP status of 200
to a GET
or HEAD
request are cached by our Smart CDN. Other status codes are never cached.
Additionally, the following are not cached:
- Responses that exceed 10MB in content length.
- Requests that contain the
Range
header. - Requests that contain the
Authorization
orPragma
headers. - Responses that contain the
no-cache
directive in theirCache-Control
headers.
Cache Control
When providing a Cache-Control
is sent from your Serverless Function, it can include any of the following directives, separated by a comma:
s-maxage=N
maxage=N, public
maxage=N, immutable
N
is the number of seconds the response should be cached for.As an example, you can set the Cache-Control
header in your Node.js Serverless Functions by using the response.setHeader
method:
module.exports = (request, response) => { response.setHeader('Cache-Control', 's-maxage=86400') response.send('Hello world!') }
Recommended Cache-Control
We recommend that you set your cache to have maxage=0, s-maxage=86400
, with changing 86400
to the amount of seconds you want your response to be cached for.
This recommendation will tell browsers not to cache and let our edge cache the responses and invalidate when your deployments update, so you never have to worry about stale content.
stale-while-revalidate
The Smart CDN supports a powerful recent extension to the Cache-Control
header called stale-while-revalidate
.
The benefit of using stale-while-revalidate
is that we can serve a resource from our CDN cache while simultaneously updating the cache in the background with the response from your Serverless Function.
Some situations where stale-while-revalidate
is of great value:
- Your content changes frequently but it takes a significant amount of time to regenerate. For example, an expensive database query or upstream API request.
- Your content changes infrequently but you want to have the flexibility to update it (to fix a typo, for example) and don't wait for cache to expire.
In both cases, we recommend using:
Cache-Control: s-maxage=1, stale-while-revalidate
Which tells our CDN: serve from cache, but update it, if requested after 1 second.
When the CDN receives a request with Pragma: no-cache
(such as when the browser devtools are open), it will revalidate any stale resource synchronously, instead of in the background.
Cache Invalidation and Purging
Every time you deploy with a target (production or staging custom domain), the cache for that target is purged. This means that users will never see content from a previous deployment on your custom domain and there is no need to invalidate it manually when deploying.