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feat(compute/metadata): retry error when talking to metadata service #4648

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Aug 19, 2021
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18 changes: 16 additions & 2 deletions compute/metadata/metadata.go
Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,8 @@ import (
"strings"
"sync"
"time"

"github.com/googleapis/gax-go/v2"
)

const (
Expand Down Expand Up @@ -304,8 +306,20 @@ func (c *Client) getETag(suffix string) (value, etag string, err error) {
}
req.Header.Set("Metadata-Flavor", "Google")
req.Header.Set("User-Agent", userAgent)
res, err := c.hc.Do(req)
if err != nil {
var res *http.Response
retryer := newRetryer()
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for {
var err error
res, err = c.hc.Do(req)
if err == nil {
break
}
if delay, shouldRetry := retryer.Retry(res.StatusCode, err); shouldRetry {
if err := gax.Sleep(context.Background(), delay); err != nil {
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return "", "", err
}
continue
}
return "", "", err
}
defer res.Body.Close()
Expand Down
77 changes: 77 additions & 0 deletions compute/metadata/retry.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,77 @@
// Copyright 2021 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package metadata

import (
"io"
"time"

"github.com/googleapis/gax-go/v2"
)

const (
maxRetryAttempts = 5
)

var (
syscallRetryable = func(err error) bool { return false }
)

func newRetryer() *metadataRetryer {
return &metadataRetryer{bo: &gax.Backoff{Initial: 100 * time.Millisecond}}
}

type backoff interface {
Pause() time.Duration
}

type metadataRetryer struct {
bo backoff
attempts int
}

func (r *metadataRetryer) Retry(status int, err error) (time.Duration, bool) {
retryOk := shouldRetry(status, err)
if !retryOk {
return 0, false
}
if r.attempts == maxRetryAttempts {
return 0, false
}
r.attempts++
return r.bo.Pause(), true
}

func shouldRetry(status int, err error) bool {
if 500 <= status && status <= 599 {
return true
}
if err == io.ErrUnexpectedEOF {
return true
}
// Transient network errors should be retried.
if syscallRetryable(err) {
return true
}
if err, ok := err.(interface{ Temporary() bool }); ok {
if err.Temporary() {
return true
}
}
if err, ok := err.(interface{ Unwrap() error }); ok {
return shouldRetry(status, err.Unwrap())
}
return false
}
25 changes: 25 additions & 0 deletions compute/metadata/retry_linux.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,25 @@
// Copyright 2021 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// +build linux

package metadata

import "syscall"

func init() {
// Initialize syscallRetryable to return true on transient socket-level
// errors. These errors are specific to Linux.
syscallRetryable = func(err error) bool { return err == syscall.ECONNRESET || err == syscall.ECONNREFUSED }
}
39 changes: 39 additions & 0 deletions compute/metadata/retry_linux_test.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,39 @@
// Copyright 2021 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// +build linux

package metadata

import (
"syscall"
"testing"
)

func TestMetadataRetryerLinux(t *testing.T) {
retryer := metadataRetryer{bo: constantBackoff{}}

t.Run("retry on syscall.ECONNRESET", func(t *testing.T) {
_, shouldRetry := retryer.Retry(400, syscall.ECONNRESET)
if !shouldRetry {
t.Fatal("retryer.Retry(500, nil) = false, want true")
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}
})
t.Run("retry on syscall.ECONNREFUSED", func(t *testing.T) {
_, shouldRetry := retryer.Retry(400, syscall.ECONNREFUSED)
if !shouldRetry {
t.Fatal("retryer.Retry(500, nil) = false, want true")
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}
})
}
108 changes: 108 additions & 0 deletions compute/metadata/retry_test.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,108 @@
// Copyright 2021 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package metadata

import (
"io"
"testing"
"time"
)

type constantBackoff struct{}

func (b constantBackoff) Pause() time.Duration { return 100 }

type errTemp struct{}

func (e errTemp) Error() string { return "temporary error" }

func (e errTemp) Temporary() bool { return true }

type errWrapped struct {
e error
}

func (e errWrapped) Error() string { return "unwrap me to get more context" }

func (e errWrapped) Unwrap() error { return e.e }

func TestMetadataRetryer(t *testing.T) {
t.Run("retry on 500", func(t *testing.T) {
retryer := metadataRetryer{bo: constantBackoff{}}
delay, shouldRetry := retryer.Retry(500, nil)
if !shouldRetry {
t.Fatal("retryer.Retry(500, nil) = false, want true")
}
if delay != 100 {
t.Fatalf("retryer.Retry(500, nil) = %d, want 100", delay)
}
})
t.Run("don't retry 400", func(t *testing.T) {
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retryer := metadataRetryer{bo: constantBackoff{}}
delay, shouldRetry := retryer.Retry(400, io.EOF)
if shouldRetry {
t.Fatal("retryer.Retry(400, io.EOF) = true, want false")
}
if delay != 0 {
t.Fatalf("retryer.Retry(400, io.EOF) = %d, want 0", delay)
}
})
t.Run("retry on io.ErrUnexpectedEOF", func(t *testing.T) {
retryer := metadataRetryer{bo: constantBackoff{}}
_, shouldRetry := retryer.Retry(400, io.ErrUnexpectedEOF)
if !shouldRetry {
t.Fatal("retryer.Retry(400, io.ErrUnexpectedEOF) = false, want true")
}
})
t.Run("retry on temporary error", func(t *testing.T) {
retryer := metadataRetryer{bo: constantBackoff{}}
err := errTemp{}
_, shouldRetry := retryer.Retry(400, err)
if !shouldRetry {
t.Fatal("retryer.Retry(400, err) = false, want true")
}
})
t.Run("retry on wrapped temporary error", func(t *testing.T) {
retryer := metadataRetryer{bo: constantBackoff{}}
err := errWrapped{errTemp{}}
_, shouldRetry := retryer.Retry(400, err)
if !shouldRetry {
t.Fatal("retryer.Retry(400, err) = false, want true")
}
})
t.Run("don't retry on wrapped io.EOF", func(t *testing.T) {
retryer := metadataRetryer{bo: constantBackoff{}}
err := errWrapped{io.EOF}
_, shouldRetry := retryer.Retry(400, err)
if shouldRetry {
t.Fatal("retryer.Retry(400, err) = true, want false")
}
})
t.Run("stop retry after 5 attempts", func(t *testing.T) {
retryer := metadataRetryer{bo: constantBackoff{}}
for i := 1; i <= 6; i++ {
_, shouldRetry := retryer.Retry(500, nil)
if i == 6 {
if shouldRetry {
t.Fatal("an error should only be retried 5 times")
}
break
}
if !shouldRetry {
t.Fatalf("retryer.Retry(500, nil) = false, want true")
}
}
})
}