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plugins/forward: Add max_concurrent option (#3640)

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* count and limit concurrent queries

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

* add option

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

* return servfail when limit exceeded

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

* docs

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

* docs

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

* docs

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

* review feedback

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

* move atomic counter to beginning of struct

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

* add comment for ErrLimitExceeded

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

* rename option to max_concurrent

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

* add metric

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

* response REFUSED; incl max in error; add more docs

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

* avoid err setup race

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

* respond SERVFAIL; doc memory usage

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>
This commit is contained in:
Chris O'Haver 2020-02-04 07:59:08 -05:00 • committed by GitHub
parent 8724a134c4
commit 22cd28a798
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5 changed files with 85 additions and 2 deletions
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17
plugin/forward/forward.go
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@ -8,6 +8,7 @@ import (
"context"
"crypto/tls"
"errors"
"sync/atomic"
"time"
"github.com/coredns/coredns/plugin"
@ -25,6 +26,8 @@ var log = clog.NewWithPlugin("forward")
// Forward represents a plugin instance that can proxy requests to another (DNS) server. It has a list
// of proxies each representing one upstream proxy.
type Forward struct {
concurrent int64 // atomic counters need to be first in struct for proper alignment
proxies []*Proxy
p policy.Policy
hcInterval time.Duration
@ -36,9 +39,14 @@ type Forward struct {
tlsServerName string
maxfails uint32
expire time.Duration
maxConcurrent int64
opts options // also here for testing
// ErrLimitExceeded indicates that a query was rejected because the number of concurrent queries has exceeded
// the maximum allowed (maxConcurrent)
ErrLimitExceeded error
Next plugin.Handler
}
@ -68,6 +76,15 @@ func (f *Forward) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg
return plugin.NextOrFailure(f.Name(), f.Next, ctx, w, r)
}
if f.maxConcurrent > 0 {
count := atomic.AddInt64(&(f.concurrent), 1)
defer atomic.AddInt64(&(f.concurrent), -1)
if count > f.maxConcurrent {
MaxConcurrentRejectCount.Add(1)
return dns.RcodeServerFailure, f.ErrLimitExceeded
}
}
fails := 0
var span, child ot.Span
var upstreamErr error