* Add metrics for cache hits/misses

Add counters for cache middleware hits and misses.

* Add test for cache middleware hit/miss counters.

* Fix cache hit metric incrementing.

* Add cache hit/miss metrics to dnssec middleware.

* Update README metric documentation.

* Add ServiceBackend interface

This adds a ServiceBackend interface that is shared between etcd/etcd3
(later) and kubernetes, leading to a massive reduction in code. When
returning the specific records from their backend.

Fixes #273

Fix the metrics test, top-level test directory still referenced the
old metrics name.

Cleanup names/typos to match standard naming conventions.

ListenAddr is the address where the prometheus metric are exported.
This can be used in tests to listen on "localhost:0" and then later
retrieve the metrics from there. It makes the tests indepent on each
other.

When a file is moved into position we should also reload the zones'
content.

This also fixes deadlock bug in the locking, a reload would block any
further lookups.

Add a separate request duration metrics specially for proxying requests
upstream.

Fixes #259

Add the rcode to the cached item and use this when we synthesize the
answer again. We could also infer the rcode from the reassembled
message, but this seems easier and is only an integer.

Also set the autoritative bit to 0 for all from-cache answers.

Fixes 357

This add a highlevel integration test for zone reloading. It also
fixes a data race in the actual reloading process.

- Implementing MX round-robin
- Slight tidy

* middleware/metrics: add more metrics

middleware/cache:
Add metrics for number of elements in the cache. Also export the total
size. Update README to detail the new metrics.

middleware/metrics

Move metrics into subpackage called "vars". This breaks the import
cycle and is cleaner. This allows vars.Report to be used in the
the dnsserver to log refused queries.

middleware/metrics: tests

Add tests to the metrics framework. The metrics/test subpackage allows
scraping of the local server. Do a few test scrape of the metrics that
are defined in the metrics middleware.

This also allows metrics integration tests to check if the caching and
dnssec middleware export their metrics correctly.

* update README

* typos

* fix tests

* Add option to parse resolv.conf for proxy upstreams

* Add test and README update for resolv.conf proxy

* Run gofmt

This fix uses docker container for kubectl. Since Kubernetes docker
image hyperkube has already been downloaded and it consists of
kubectl, there is really no need to download kubectl binary again.

This fix cleans up the Kubernetes related travis setup and removes
unneeded scripts.

This fix also fixes several mismatches of the Kubernetes version used,
so that any changes in version in the future only need to update .travis.yml.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

The DS record is handled specially in the server ServeDNS mux, but there
was no code that actually called the correct middleware handler chain
when encountering a DS.

This PR fixes that behavoir, additonal bugs has been files to look into
how we are handling delegation (secure and non-secure ones).

This fix adds a `cache_capacity` option to dnssec middleware, so that
it is possible to specify the capacity of the LRU cache used by dnssec
middleware.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

Add a test which enables caching and debug queries and make sure
the debug query does not overwrite the cache.

A small golint cleanup.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

Add auto-load middleware that automatically picks up zones.

Every X seconds it will scan for new zones.
Add tests and documentation.

Make 'make test' use -race.

In the file middleware, if there are multiple zone files under a single root zone, watchers are only invoked on the last element of `zones.Names`. This is caused by loop override on the variable `n`.

This issue can be fixed by passing zone object, which calls reload watcher directly.

* Replace go-cache with golang-lru

This fix replace go-cache with golang-lru, as is specified in 335.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Move cache initialization to setup

This commit move cache initialization to setup in dnssec middleware.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

Move middleware/middleware.md to middleware.md. This should be the
canonical place where to document how middlewares should look and act.

This fix adds several needed comments in
`middleware/kubernetes/nametemplate/nametemplate.go`
to clean up golint output.

There are still 3 places that needs proper docs:
```
middleware/kubernetes/nametemplate/nametemplate.go:64:1: comment on exported type Template should be of the form "Template ..." (with optional leading article)
middleware/kubernetes/nametemplate/nametemplate.go:72:1: comment on exported method Template.SetTemplate should be of the form "SetTemplate ..."
middleware/kubernetes/nametemplate/nametemplate.go:188:1: comment on exported type NameValues should be of the form "NameValues ..." (with optional leading article)
```
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

Go vet and golint the new code once again.

Drop Name from NameTemplate - it's cleaner: nametemplate.Template.

This PR adds the *root* middleware that specifies a path where
all zone file (the *file* middleware is the only consumer now) can
be found. It works the same as in Caddy.

Documentation can be found in the README.md of the middleware.

Fixes #307

This fix adds a unit test for DuplicateCNAME to have
a basic coverage for dnsutil.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

This fix adds unit tests for `ExtractAddressFromReverse`. It also
updates the implementation of `ExtractAddressFromReverse` so that
only a valid IPv4 or IPv6 address (in string format) is returned.

If the addresses is not valid and can not be handled by golang's
`net.ParseIP` then an empty string (`""`) will be returned.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

This still needs cleanup, but this is a first pass the cleans some
cruft and documents our style (in middleware.md) and makes all the
docs match that style.

Add the ability to add a class of responses to be logged; success,
denial or error. The default is to log everything (all).

Fixes #258

Make tests compile; failed to catch this due to use of tags for this
part of the (test) code.

Some document improvements and add a few more tests.