Reloading should work (kill -TERM reload the coredns process), but a lot
of plugins can't handle it proper. Disable to reload plugin until we fix
(most) of the plugins
This fix is an enhancement of external plugin enabling.
Previously, it was already able to build a customerized
coredns with plugins enabled selectively, without changing
coredns source code. However, all default plugins are
actually bundled because of the import rule:
```
"github.com/coredns/coredns/coremain"
```
The issue is best described with the following:
```
root@localhost:/go/src/github.com/coredns/coredns/sample# cat sample.go
package main
import (
_ "github.com/coredns/forward"
"github.com/coredns/coredns/coremain"
"github.com/coredns/coredns/core/dnsserver"
)
var directives = []string{
"forward",
"startup",
"shutdown",
}
func init() {
dnsserver.Directives = directives
}
func main() {
coremain.Run()
}
root@localhost:/go/src/github.com/coredns/coredns/sample#
root@localhost:/go/src/github.com/coredns/coredns/sample# go build -v sample.go
root@localhost:/go/src/github.com/coredns/coredns/sample# ./sample -plugins
root@localhost:/go/src/github.com/coredns/coredns/sample# ./sample -plugins
Server types:
dns
Caddyfile loaders:
flag
default
Other plugins:
dns.auto
dns.autopath
dns.bind
dns.cache
dns.chaos
dns.debug
dns.dnssec
dns.dnstap
dns.erratic
dns.errors
dns.etcd
dns.federation
dns.file
dns.forward
dns.health
dns.hosts
dns.kubernetes
dns.loadbalance
dns.log
dns.nsid
dns.pprof
dns.prometheus
dns.proxy
dns.reverse
dns.rewrite
dns.root
dns.route53
dns.secondary
dns.template
....
```
This fix moves zplugins.go to a different package/directory so that
it is possible to "only import plugins as needed".
The following is the new output after this fix:
```
root@localhost:/go/src/github.com/coredns/coredns/sample# ./sample -plugins
Server types:
dns
Caddyfile loaders:
flag
default
Other plugins:
dns.forward
dns.prometheus
shutdown
startup
root@localhost:/go/src/github.com/coredns/coredns/sample#
```
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
