Default to upstream to self (#2436)

* Default to upstream to self

This is a backwards incompatible change.

This is a massive (cleanup) PR where we default to resolving external
names by the coredns process itself, instead of directly forwarding them
to some upstream.

This ignores any arguments `upstream` may have had and makes it depend
on proxy/forward configuration in the Corefile. This allows resolved
upstream names to be cached and we have better healthchecking of the
upstreams. It also means there is only one way to resolve names, by
either using the proxy or forward plugin.

The proxy/forward lookup.go functions have been removed. This also
lessen the dependency on proxy, meaning deprecating proxy will become
easier. Some tests have been removed as well, or moved to the top-level
test directory as they now require a full coredns process instead of
just the plugin.

For the etcd plugin, the entire StubZone resolving is *dropped*! This
was a hacky (but working) solution to say the least. If someone cares
deeply it can be brought back (maybe)?

The pkg/upstream is now very small and almost does nothing. Also the
New() function was changed to return a pointer to upstream.Upstream. It
also returns only one parameter, so any stragglers using it will
encounter a compile error.

All documentation has been adapted. This affected the following plugins:
* etcd
* file
* auto
* secondary
* federation
* template
* route53

A followup PR will make any upstream directives with arguments an error,
right now they are ignored.

Signed-off-by: Miek Gieben <miek@miek.nl>

* Fix etcd build - probably still fails unit test

Signed-off-by: Miek Gieben <miek@miek.nl>

* Slightly smarter lookup check in upstream

Signed-off-by: Miek Gieben <miek@miek.nl>

* Compilez

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/etcd/README.md

@@ -28,28 +28,22 @@ If you want to `round robin` A and AAAA responses look at the `loadbalance` plug
 
 ~~~
 etcd [ZONES...] {
-    stubzones
     fallthrough [ZONES...]
     path PATH
     endpoint ENDPOINT...
-    upstream [ADDRESS...]
+    upstream
     tls CERT KEY CACERT
 }
 ~~~
 
-* `stubzones` enables the stub zones feature. The stubzone is *only* done in the etcd tree located
-    under the *first* zone specified.
 * `fallthrough` If zone matches but no record can be generated, pass request to the next plugin.
   If **[ZONES...]** is omitted, then fallthrough happens for all zones for which the plugin
   is authoritative. If specific zones are listed (for example `in-addr.arpa` and `ip6.arpa`), then only
   queries for those zones will be subject to fallthrough.
 * **PATH** the path inside etcd. Defaults to "/skydns".
 * **ENDPOINT** the etcd endpoints. Defaults to "http://localhost:2379".
-* `upstream` upstream resolvers to be used resolve external names found in etcd (think CNAMEs)
-  pointing to external names. If you want CoreDNS to act as a proxy for clients, you'll need to add
-  the proxy plugin. If no **ADDRESS** is given, CoreDNS will resolve CNAMEs against itself.
-  **ADDRESS** can be an IP address, and IP:port or a string pointing to a file that is structured
-  as /etc/resolv.conf.
+* `upstream` resolve names found in etcd (think CNAMEs) If you want CoreDNS to act as a proxy for clients,
+  you'll need to add the forward plugin. CoreDNS will resolve CNAMEs against itself.
 * `tls` followed by:
 
     * no arguments, if the server certificate is signed by a system-installed CA and no client cert is needed
@@ -79,10 +73,9 @@ This is the default SkyDNS setup, with everything specified in full:
 ~~~ corefile
 . {
     etcd skydns.local {
-        stubzones
         path /skydns
         endpoint http://localhost:2379
-        upstream 8.8.8.8:53 8.8.4.4:53
+        upstream
     }
     prometheus
     cache 160 skydns.local
@@ -98,7 +91,7 @@ when resolving external pointing CNAMEs.
 . {
     etcd skydns.local {
         path /skydns
-        upstream /etc/resolv.conf
+        upstream
     }
     cache 160 skydns.local
     proxy . /etc/resolv.conf
@@ -125,7 +118,6 @@ need to add the zone `0.0.10.in-addr.arpa` to the list of zones. Showing a snipp
 
 ~~~
 etcd skydns.local 10.0.0.0/24 {
-    stubzones
 ...
 ~~~