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README.md
10
README.md
@ -15,6 +15,12 @@ writing CoreDNS plugins.
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example
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example
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~~~
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~~~
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## Metrics
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If monitoring is enabled (via the *prometheus* directive) the following metric is exported:
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* `coredns_example_request_count_total{server}` - query count to the *example* plugin.
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## Examples
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## Examples
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In this configuration, we forward all queries to 9.9.9.9 and print "example" whenever we recieve
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In this configuration, we forward all queries to 9.9.9.9 and print "example" whenever we recieve
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@ -26,3 +32,7 @@ a query.
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example
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example
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}
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}
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```
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```
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## Also See
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See the [manual](https://coredns.io/manual).
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@ -1,4 +1,6 @@
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// The example plugin prints example to stdout on every packet received.
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// Package example is a CoreDNS plugin that prints "example" to stdout on every packet received.
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//
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// It serves as an example CoreDNS plugin with numerous code comments.
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package example
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package example
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import (
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import (
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@ -7,6 +9,7 @@ import (
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"os"
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"os"
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"github.com/coredns/coredns/plugin"
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"github.com/coredns/coredns/plugin"
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"github.com/coredns/coredns/plugin/metrics"
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"github.com/miekg/dns"
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"github.com/miekg/dns"
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"golang.org/x/net/context"
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"golang.org/x/net/context"
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@ -28,6 +31,9 @@ func (e Example) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg)
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// Wrap.
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// Wrap.
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pw := NewResponsePrinter(w)
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pw := NewResponsePrinter(w)
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// Export metric with the server label set to the current server handling the request.
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requestCount.WithLabelValues(metrics.WithServer(ctx)).Add(1)
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// Call next plugin (if any).
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// Call next plugin (if any).
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return plugin.NextOrFailure(e.Name(), e.Next, ctx, pw, r)
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return plugin.NextOrFailure(e.Name(), e.Next, ctx, pw, r)
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}
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}
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20
metrics.go
Normal file
20
metrics.go
Normal file
@ -0,0 +1,20 @@
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package example
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import (
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"sync"
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"github.com/coredns/coredns/plugin"
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"github.com/prometheus/client_golang/prometheus"
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)
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// requestCount exports a prometheus metric that is incremented every time
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// a query is seen by the example plugin.
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var requestCount = prometheus.NewCounterVec(prometheus.CounterOpts{
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Namespace: plugin.Namespace,
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Subsystem: "example",
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Name: "request_count_total",
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Help: "Counter of requests made.",
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}, []string{"server"})
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var once sync.Once
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9
setup.go
9
setup.go
@ -3,6 +3,7 @@ package example
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import (
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import (
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"github.com/coredns/coredns/core/dnsserver"
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"github.com/coredns/coredns/core/dnsserver"
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"github.com/coredns/coredns/plugin"
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"github.com/coredns/coredns/plugin"
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"github.com/coredns/coredns/plugin/metrics"
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"github.com/mholt/caddy"
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"github.com/mholt/caddy"
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)
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)
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@ -27,6 +28,14 @@ func setup(c *caddy.Controller) error {
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return plugin.Error("example", c.ArgErr())
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return plugin.Error("example", c.ArgErr())
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}
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}
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// Add a startup function that will -- after all plugins have been loaded -- check if the
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// prometheus plugin has been used - if so we will export metrics. We can only register
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// this metric once, hence the "once.Do".
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c.OnStartup(func() error {
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once.Do(func() { metrics.MustRegister(c, requestCount) })
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return nil
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})
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// Add the Plugin to CoreDNS, so Servers can use it in their plugin chain.
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// Add the Plugin to CoreDNS, so Servers can use it in their plugin chain.
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dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
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dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
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return Example{Next: next}
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return Example{Next: next}
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