Fallback on resolution failure

This allows switching to a fallback forwarding configuration on queries where the resolver is unable to contact upstream servers.

fallback:
  enable: true
  servers:
    - address: [ 2001:148f:fffe::1, 193.17.47.1 ]
      transport: tls
      hostname: odvr.nic.cz

The servers: has the same schema as in forwarding.

If you use fallback within a fleet of servers, you will probably want to avoid queries cycling in there, i.e. disable the fallback option for them in views.