# fallback

## Deprecated

This plugin is deprecated in favor of https://github.com/coredns/alternate, which performs the same function.

## Name

*fallback* - a plugin that sends queries to an alternate set of upstreams if the plugin
chain returns specific error messages.

## Description

The *fallback* plugin allows an alternate set of upstreams be specified which will be used
if the plugin chain returns specific error messages. The *fallback* plugin utilizes the *proxy* plugin (<https://coredns.io/plugins/proxy>) to query the specified upstreams.

As the name suggests, the purpose of the *fallback* is to allow a fallback when, for example,
the desired upstreams became unavailable.

## Syntax

```
{
    fallback [original] RCODE PROXY_PARAMS
}
```

* **original** is optional flag. If it is set then fallback uses original request instead of potentially changed by other plugins
* **RCODE** is the string representation of the error response code. The complete list of valid rcode strings are defined as `RcodeToString` in <https://github.com/miekg/dns/blob/master/msg.go>, examples of which are `SERVFAIL`, `NXDOMAIN` and `REFUSED`.
* **PROXY_PARAMS** accepts the same parameters as the *proxy* plugin
<https://coredns.io/plugins/proxy>.

## Examples

### Fallback to local DNS server

The following specifies that all requests are proxied to 8.8.8.8. If the response is `NXDOMAIN`, *fallback* will proxy the request to 192.168.1.1:53, and reply to client accordingly.

```
. {
	proxy . 8.8.8.8
	fallback NXDOMAIN . 192.168.1.1:53
	log
}

```
### Fallback with original request used

The following specify that `original` query will be proxied to 192.168.1.1:53 if 8.8.8.8 response is `NXDOMAIN`. `original` means no changes from next plugins on request. With no `original` flag fallback will proxy request with EDNS0 option (set by rewrite).

```
. {
	proxy . 8.8.8.8
    rewrite edns0 local set 0xffee 0x61626364
	fallback original NXDOMAIN . 192.168.1.1:53
	log
}

```

### Multiple fallbacks

Multiple fallbacks can be specified, as long as they serve unique error responses.

```
. {
    proxy . 8.8.8.8
    fallback NXDOMAIN . 192.168.1.1:53
    fallback REFUSED . 192.168.100.1:53
    fallback original SERVFAIL . 192.168.100.1:53
    log
}

```

### Additional proxy parameters

You can specify additional proxy parameters for each of the fallback upstreams.

```
. {
    proxy . 8.8.8.8
    fallback NXDOMAIN . 192.168.1.1:53 192.168.1.2:53 {
        protocol dns force_tcp
    }
    log
}
```