---
title: bereq.first_byte_timeout
summary: null
url: >-
  https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/bereq-first-byte-timeout
---

**Type:** RTIME  
**Access:** can be read and set, but not unset

**Available in:** pass, miss

The amount of time Fastly should wait for a backend server to deliver the first byte of an HTTP response body, before triggering a timeout.

May be set to any value between `0` and `600s`. By default, the timeout is `15s`.

If the timeout is triggered, Fastly will create an error object and invoke `vcl_error` with `obj.status` set to `503` and `obj.response` set to `"first byte timeout"`.  [Learn more about errors](https://www.fastly.com/documentation/guides/concepts/errors).

## Effects of clustering

If [clustering](https://www.fastly.com/documentation/guides/vcl/clustering/), the request will pass through more than one Fastly server before it is sent to the origin. The timeout between nodes in a cluster is **always 60s and is not configurable**. This means that, for services with clustering enabled, the effective maximum `bereq.first_byte_timeout` is 60s.

The timeout between POPs in a shielding arrangement is affected by the settings in each case, since the full VCL configuration will be executed at each POP separately. For example, to set a timeout that applies only when connecting to the origin and not when connecting to an upstream shield POP, use the following VCL:

```vcl context="sub vcl_miss { ... }"
if (req.backend.is_origin) {
  set bereq.first_byte_timeout = 10s;
}
```

### Longer timeouts

To set a timeout of more than 60 seconds, you must perform the request without clustering. You can do this in two ways, both of which significantly impact Fastly's ability to cache your content:

- Mark the request as a **PASS** by executing `return(pass)` in `vcl_recv`. Responses will not be cached.
- Disable [clustering](https://www.fastly.com/documentation/guides/vcl/clustering/). Cache hit ratio will be severely reduced.

In such cases, consider limiting this behavior to only the URLs that require an extreme timeout. For example, the following code sets a five-minute first byte timeout for all requests to paths starting with `/slow/response`:

```vcl context="sub vcl_miss { ... }, sub vcl_pass { ... }"
if (req.url ~ "^/slow/response") {
  set bereq.first_byte_timeout = 300s;
}
```