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Add *ready* plugin (#2616)

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Add a ready plugin that allows plugin to signal when they are ready.
Once a plugin is ready it is not queried again.

This uses same mechanism as the health plugin: each plugin needs to
implement an interface.

Implement readines for the *erratic* plugin to aid in testing.

Add README.md and tests moduled after the health plugin; which will be
relegated to just providing process health. In similar vein to health
this is a process wide setting.

With this Corefile:
~~~
. {
    erratic
    whoami
    ready
}

bla {
    erratic
    whoami
}
~~~

ready will lead to:

~~~ sh
% curl localhost:8181/ready
% dig @localhost -p 1053 mx example.org
% curl localhost:8181/ready
OK%
~~~

Meanwhile CoreDNS logs:

~~~
.:1053
bla.:1053
2019-02-26T20:59:07.137Z [INFO] CoreDNS-1.3.1
2019-02-26T20:59:07.137Z [INFO] linux/amd64, go1.11.4,
CoreDNS-1.3.1
linux/amd64, go1.11.4,
2019-02-26T20:59:11.415Z [INFO] plugin/ready: Still waiting on: "erratic"
2019-02-26T20:59:13.510Z [INFO] plugin/ready: Still waiting on: "erratic"
~~~

*ready* can be used in multiple server blocks and will do the right
thing; query all those plugins from all server blocks for readiness.
This does a similar thing to the prometheus plugin.

Signed-off-by: Miek Gieben <miek@miek.nl>
This commit is contained in:
Miek Gieben 2019-03-07 20:35:16 +00:00 • committed by GitHub
parent 2b7e84a076
commit db0b16b615
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13 changed files with 409 additions and 2 deletions
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81
plugin/ready/ready_test.go Normal file
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package ready
import (
"context"
"fmt"
"net/http"
"sync"
"testing"
"github.com/coredns/coredns/plugin/erratic"
clog "github.com/coredns/coredns/plugin/pkg/log"
"github.com/coredns/coredns/plugin/test"
"github.com/miekg/dns"
)
func init() { clog.Discard() }
func TestReady(t *testing.T) {
rd := &ready{Addr: ":0"}
e := &erratic.Erratic{}
plugins.Append(e, "erratic")
wg := sync.WaitGroup{}
wg.Add(1)
go func() {
if err := rd.onStartup(); err != nil {
t.Fatalf("Unable to startup the readiness server: %v", err)
}
wg.Done()
}()
wg.Wait()
defer rd.onFinalShutdown()
address := fmt.Sprintf("http://%s/ready", rd.ln.Addr().String())
wg.Add(1)
go func() {
response, err := http.Get(address)
if err != nil {
t.Fatalf("Unable to query %s: %v", address, err)
}
if response.StatusCode != 503 {
t.Errorf("Invalid status code: expecting %d, got %d", 503, response.StatusCode)
}
response.Body.Close()
wg.Done()
}()
wg.Wait()
// make it ready by giving erratic 3 queries.
m := new(dns.Msg)
m.SetQuestion("example.org.", dns.TypeA)
e.ServeDNS(context.TODO(), &test.ResponseWriter{}, m)
e.ServeDNS(context.TODO(), &test.ResponseWriter{}, m)
e.ServeDNS(context.TODO(), &test.ResponseWriter{}, m)
response, err := http.Get(address)
if err != nil {
t.Fatalf("Unable to query %s: %v", address, err)
}
if response.StatusCode != 200 {
t.Errorf("Invalid status code: expecting %d, got %d", 200, response.StatusCode)
}
response.Body.Close()
// make erratic not-ready by giving it more queries, this should not change the process readiness
e.ServeDNS(context.TODO(), &test.ResponseWriter{}, m)
e.ServeDNS(context.TODO(), &test.ResponseWriter{}, m)
e.ServeDNS(context.TODO(), &test.ResponseWriter{}, m)
response, err = http.Get(address)
if err != nil {
t.Fatalf("Unable to query %s: %v", address, err)
}
if response.StatusCode != 200 {
t.Errorf("Invalid status code: expecting %d, got %d", 200, response.StatusCode)
}
response.Body.Close()
}