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feat: generate RSA key lazily for lazy refresh (#589)
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When lazy refresh is enabled, the RSA key generation will not occur
until a client calls Dial. This change helps cold start times in
serverless environments.

Prior to this commit, the RSA key generation was done at the package
level using globals. This commit removes the use of globals and moves
the key generation into the dialer. This means multiple dialers will now
have multiple RSA keys. Before this commit, multiple dialers all shared
the same RSA key. If this is a concern, callers may still configure
their own RSA key across multiple dialers.

Fixes #584
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enocom authored Jun 6, 2024
1 parent 519a9ac commit f106169
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Showing 2 changed files with 214 additions and 22 deletions.
76 changes: 54 additions & 22 deletions dialer.go
Original file line number Diff line number Diff line change
Expand Up @@ -63,18 +63,47 @@ var (
//go:embed version.txt
versionString string
userAgent = "alloydb-go-connector/" + strings.TrimSpace(versionString)

// defaultKey is the default RSA public/private keypair used by the clients.
defaultKey *rsa.PrivateKey
defaultKeyErr error
keyOnce sync.Once
)

func getDefaultKeys() (*rsa.PrivateKey, error) {
keyOnce.Do(func() {
defaultKey, defaultKeyErr = rsa.GenerateKey(rand.Reader, 2048)
})
return defaultKey, defaultKeyErr
// keyGenerator encapsulates the details of RSA key generation to provide lazy
// generation, custom keys, or a default RSA generator.
type keyGenerator struct {
once sync.Once
key *rsa.PrivateKey
err error
genFunc func() (*rsa.PrivateKey, error)
}

// newKeyGenerator initializes a keyGenerator that will (in order):
// - always return the RSA key if one is provided, or
// - generate an RSA key lazily when it's requested, or
// - (default) immediately generate an RSA key as part of the initializer.
func newKeyGenerator(
k *rsa.PrivateKey, lazy bool, genFunc func() (*rsa.PrivateKey, error),
) (*keyGenerator, error) {
g := &keyGenerator{genFunc: genFunc}
switch {
case k != nil:
// If the caller has provided a key, initialize the key and consume the
// sync.Once now.
g.once.Do(func() { g.key, g.err = k, nil })
case lazy:
// If lazy refresh is enabled, do nothing and wait for the call to
// rsaKey.
default:
// If no key has been provided and lazy refresh isn't enabled, generate
// the key and consume the sync.Once now.
g.once.Do(func() { g.key, g.err = g.genFunc() })
}
return g, g.err
}

// rsaKey will generate an RSA key if one is not already cached. Otherwise, it
// will return the cached key.
func (g *keyGenerator) rsaKey() (*rsa.PrivateKey, error) {
g.once.Do(func() { g.key, g.err = g.genFunc() })

return g.key, g.err
}

type connectionInfoCache interface {
Expand All @@ -96,7 +125,7 @@ type monitoredCache struct {
type Dialer struct {
lock sync.RWMutex
cache map[alloydb.InstanceURI]monitoredCache
key *rsa.PrivateKey
keyGenerator *keyGenerator
refreshTimeout time.Duration
// closed reports if the dialer has been closed.
closed chan struct{}
Expand Down Expand Up @@ -158,14 +187,6 @@ func NewDialer(ctx context.Context, opts ...Option) (*Dialer, error) {
// Add this to the end to make sure it's not overridden
cfg.adminOpts = append(cfg.adminOpts, option.WithUserAgent(userAgent))

if cfg.rsaKey == nil {
key, err := getDefaultKeys()
if err != nil {
return nil, fmt.Errorf("failed to generate RSA keys: %v", err)
}
cfg.rsaKey = key
}

// If no token source is configured, use ADC's token source.
ts := cfg.tokenSource
if ts == nil {
Expand All @@ -192,12 +213,19 @@ func NewDialer(ctx context.Context, opts ...Option) (*Dialer, error) {
if err := trace.InitMetrics(); err != nil {
return nil, err
}
g, err := newKeyGenerator(cfg.rsaKey, cfg.lazyRefresh,
func() (*rsa.PrivateKey, error) {
return rsa.GenerateKey(rand.Reader, 2048)
})
if err != nil {
return nil, err
}
d := &Dialer{
closed: make(chan struct{}),
cache: make(map[alloydb.InstanceURI]monitoredCache),
lazyRefresh: cfg.lazyRefresh,
staticConnInfo: cfg.staticConnInfo,
key: cfg.rsaKey,
keyGenerator: g,
refreshTimeout: cfg.refreshTimeout,
client: client,
logger: cfg.logger,
Expand Down Expand Up @@ -570,13 +598,17 @@ func (d *Dialer) connectionInfoCache(
"[%v] Connection info added to cache",
uri.String(),
)
k, err := d.keyGenerator.rsaKey()
if err != nil {
return monitoredCache{}, err
}
var cache connectionInfoCache
switch {
case d.lazyRefresh:
cache = alloydb.NewLazyRefreshCache(
uri,
d.logger,
d.client, d.key,
d.client, k,
d.refreshTimeout, d.dialerID,
)
case d.staticConnInfo != nil:
Expand All @@ -593,7 +625,7 @@ func (d *Dialer) connectionInfoCache(
cache = alloydb.NewRefreshAheadCache(
uri,
d.logger,
d.client, d.key,
d.client, k,
d.refreshTimeout, d.dialerID,
)
}
Expand Down
160 changes: 160 additions & 0 deletions key_gen_test.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,160 @@
// Copyright 2024 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
//
// https://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 alloydbconn

import (
"crypto/rsa"
"errors"
"testing"
)

func TestKeyGenerator(t *testing.T) {
custom := &rsa.PrivateKey{}
generated := &rsa.PrivateKey{}

var (
defaultCount int
lazyCount int
)

tcs := []struct {
desc string
key *rsa.PrivateKey
lazy bool
genFunc func() (*rsa.PrivateKey, error)
wantKey *rsa.PrivateKey
// whether key generation should happen in the initializer or the call
// to rsaKey
wantLazy bool
}{
{
desc: "by default a key is generated",
genFunc: func() (*rsa.PrivateKey, error) {
return generated, nil
},
wantKey: generated,
},
{
desc: "a custom key skips the generator",
key: custom,
genFunc: func() (*rsa.PrivateKey, error) {
return nil, errors.New("generator should not be called")
},
wantKey: custom,
},
{
desc: "lazy generates keys on first request",
lazy: true,
genFunc: func() (*rsa.PrivateKey, error) {
if defaultCount > 0 {
return nil, errors.New("genFunc was called twice")
}
defaultCount++
return generated, nil
},
wantKey: generated,
wantLazy: true,
},
{
desc: "key generation happens only once",
genFunc: func() (*rsa.PrivateKey, error) {
if lazyCount > 0 {
return nil, errors.New("genFunc was called twice")
}
lazyCount++
return generated, nil
},
wantKey: generated,
},
}

for _, tc := range tcs {
t.Run(tc.desc, func(t *testing.T) {
g, err := newKeyGenerator(tc.key, tc.lazy, tc.genFunc)
if err != nil {
t.Fatal(err)
}
if tc.wantLazy && g.key != nil {
t.Fatal("want RSA key to be lazily generated, but it wasn't")
}
k, err := g.rsaKey()
if err != nil {
t.Fatal(err)
}
if tc.wantKey != k {
t.Fatalf("want = %v, got = %v", tc.wantKey, k)
}
// Ensure a second call doesn't trigger a new key generation
_, err = g.rsaKey()
if err != nil {
t.Fatal(err)
}
})
}
}

func TestKeyGeneratorErrors(t *testing.T) {
sentinel := errors.New("sentinel error")
tcs := []struct {
desc string
key *rsa.PrivateKey
lazy bool
genFunc func() (*rsa.PrivateKey, error)
wantInitError error
wantKeyError error
}{
{
desc: "generator returns errors",
genFunc: func() (*rsa.PrivateKey, error) {
return nil, sentinel
},
wantInitError: sentinel,
wantKeyError: sentinel,
},
{
desc: "custom keys never error",
key: &rsa.PrivateKey{},
genFunc: func() (*rsa.PrivateKey, error) {
return nil, errors.New("generator should not be called")
},
wantInitError: nil,
wantKeyError: nil,
},
{
desc: "lazy generation returns errors",
lazy: true,
genFunc: func() (*rsa.PrivateKey, error) {
return nil, sentinel
},
// initialization should succeed
wantInitError: nil,
// but requesting the key later should fail
wantKeyError: sentinel,
},
}

for _, tc := range tcs {
t.Run(tc.desc, func(t *testing.T) {
g, err := newKeyGenerator(tc.key, tc.lazy, tc.genFunc)
if err != tc.wantInitError {
t.Fatal("initialization should fail, but did not")
}
_, err = g.rsaKey()
if err != tc.wantKeyError {
t.Fatal("rsaKey should fail but didn't")
}
})
}
}

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