---
title: HTTP/2 server push
summary: null
url: >-
  https://www.fastly.com/documentation/guides/full-site-delivery/performance/http2-server-push
---

HTTP/2 server push allows you to set up rules that enable Fastly to pre-emptively load and then send responses to an HTTP/2-compliant client before that client requests them. You can initiate an HTTP/2 server push via a response header or VCL function.

## Server push with the `link` response header

Fastly recognizes `link` headers with the [preload keyword](https://w3c.github.io/preload/) sent by an origin server and pushes the designated resource to a client. For example, this `link` response header triggers an HTTP/2 push:

```vcl
link: </assets/jquery.js>; rel=preload; as=script
```

We support multiple `link` headers and multiple assets in one `link` title:

```vcl
link: </assets/jquery.js>; rel=preload; as=script, </assets/base.css>; rel=preload; as=style
```

Additional attributes used in the `link` header can further control server push and how the header itself is handled. If no additional attributes are included, the `link` header will trigger server push and be forwarded to the client:

```vcl
link: </assets/jquery.js>; rel=preload; as=script
```

If used with the `nopush` directive, the header will _not_ trigger a push and will be passed as is to the client:

```vcl
link: </assets/jquery.js>; rel=preload; as=script; nopush
```

If used with the `x-http2-push-only` directive, the header will trigger a server push but will be subsequently removed and not forwarded to the client:

```vcl
link: </assets/jquery.js>; rel=preload; as=script; x-http2-push-only
```

The attributes can be mixed and matched if needed:

```vcl
link: </assets/jquery.js>; rel=preload; as=script, </assets/base.css>; rel=preload; as=style; nopush, </assets/main.css>; rel=preload; as=style; x-http2-push-only
```

### Link headers and Amazon S3 buckets

If you're using an [Amazon Simple Storage Service (S3)](https://www.fastly.com/documentation/guides/integrations/non-fastly-services/amazon-s3) bucket as your origin server, you can still use `link` headers by [applying a cache setting condition](https://www.fastly.com/documentation/guides/full-site-delivery/caching/caching-best-practices) like this one:

`set beresp.http.Link = beresp.http.x-amz-meta-Link`

## Server push with the `h2.push()` function

Server push can also be triggered with the `h2.push()` VCL function. The asset to be pushed is passed to the function as a parameter. For example:

```vcl
sub vcl_recv {
#FASTLY recv

  if (fastly_info.is_h2 && req.url ~ "^/index.html")
  {
    h2.push("/assets/jquery.js");
  }
}
```

The `h2.push()` function triggers server push as soon as it's called, which removes the need for a `link` header to arrive with a server response. This means assets can be pushed to the client before the response for the request that triggered the push is received from the server, accelerating their delivery.

## Related content

- [Client request VCL variables](https://www.fastly.com/documentation/reference/vcl/variables/client-request/)