lib/cloud/ec2/ec2.go

   1 // Copyright (C) The Arvados Authors. All rights reserved.
   2 //
   3 // SPDX-License-Identifier: AGPL-3.0
   4
   5 package ec2
   6
   7 import (
   8         "crypto/md5"
   9         "crypto/rsa"
  10         "crypto/sha1"
  11         "crypto/x509"
  12         "encoding/base64"
  13         "encoding/json"
  14         "fmt"
  15         "math/big"
  16         "strconv"
  17         "sync"
  18         "sync/atomic"
  19         "time"
  20
  21         "git.arvados.org/arvados.git/lib/cloud"
  22         "git.arvados.org/arvados.git/sdk/go/arvados"
  23         "github.com/aws/aws-sdk-go/aws"
  24         "github.com/aws/aws-sdk-go/aws/awserr"
  25         "github.com/aws/aws-sdk-go/aws/credentials"
  26         "github.com/aws/aws-sdk-go/aws/credentials/ec2rolecreds"
  27         "github.com/aws/aws-sdk-go/aws/ec2metadata"
  28         "github.com/aws/aws-sdk-go/aws/request"
  29         "github.com/aws/aws-sdk-go/aws/session"
  30         "github.com/aws/aws-sdk-go/service/ec2"
  31         "github.com/sirupsen/logrus"
  32         "golang.org/x/crypto/ssh"
  33 )
  34
  35 // Driver is the ec2 implementation of the cloud.Driver interface.
  36 var Driver = cloud.DriverFunc(newEC2InstanceSet)
  37
  38 const (
  39         throttleDelayMin = time.Second
  40         throttleDelayMax = time.Minute
  41 )
  42
  43 type ec2InstanceSetConfig struct {
  44         AccessKeyID             string
  45         SecretAccessKey         string
  46         Region                  string
  47         SecurityGroupIDs        arvados.StringSet
  48         SubnetID                string
  49         AdminUsername           string
  50         EBSVolumeType           string
  51         EBSPrice                float64
  52         IAMInstanceProfile      string
  53         SpotPriceUpdateInterval arvados.Duration
  54 }
  55
  56 type ec2Interface interface {
  57         DescribeKeyPairs(input *ec2.DescribeKeyPairsInput) (*ec2.DescribeKeyPairsOutput, error)
  58         ImportKeyPair(input *ec2.ImportKeyPairInput) (*ec2.ImportKeyPairOutput, error)
  59         RunInstances(input *ec2.RunInstancesInput) (*ec2.Reservation, error)
  60         DescribeInstances(input *ec2.DescribeInstancesInput) (*ec2.DescribeInstancesOutput, error)
  61         DescribeInstanceStatusPages(input *ec2.DescribeInstanceStatusInput, fn func(*ec2.DescribeInstanceStatusOutput, bool) bool) error
  62         DescribeSpotPriceHistoryPages(input *ec2.DescribeSpotPriceHistoryInput, fn func(*ec2.DescribeSpotPriceHistoryOutput, bool) bool) error
  63         CreateTags(input *ec2.CreateTagsInput) (*ec2.CreateTagsOutput, error)
  64         TerminateInstances(input *ec2.TerminateInstancesInput) (*ec2.TerminateInstancesOutput, error)
  65 }
  66
  67 type ec2InstanceSet struct {
  68         ec2config              ec2InstanceSetConfig
  69         instanceSetID          cloud.InstanceSetID
  70         logger                 logrus.FieldLogger
  71         client                 ec2Interface
  72         keysMtx                sync.Mutex
  73         keys                   map[string]string
  74         throttleDelayCreate    atomic.Value
  75         throttleDelayInstances atomic.Value
  76
  77         prices        map[priceKey][]cloud.InstancePrice
  78         pricesLock    sync.Mutex
  79         pricesUpdated map[priceKey]time.Time
  80 }
  81
  82 func newEC2InstanceSet(config json.RawMessage, instanceSetID cloud.InstanceSetID, _ cloud.SharedResourceTags, logger logrus.FieldLogger) (prv cloud.InstanceSet, err error) {
  83         instanceSet := &ec2InstanceSet{
  84                 instanceSetID: instanceSetID,
  85                 logger:        logger,
  86         }
  87         err = json.Unmarshal(config, &instanceSet.ec2config)
  88         if err != nil {
  89                 return nil, err
  90         }
  91
  92         sess, err := session.NewSession()
  93         if err != nil {
  94                 return nil, err
  95         }
  96         // First try any static credentials, fall back to an IAM instance profile/role
  97         creds := credentials.NewChainCredentials(
  98                 []credentials.Provider{
  99                         &credentials.StaticProvider{Value: credentials.Value{AccessKeyID: instanceSet.ec2config.AccessKeyID, SecretAccessKey: instanceSet.ec2config.SecretAccessKey}},
 100                         &ec2rolecreds.EC2RoleProvider{Client: ec2metadata.New(sess)},
 101                 })
 102
 103         awsConfig := aws.NewConfig().WithCredentials(creds).WithRegion(instanceSet.ec2config.Region)
 104         instanceSet.client = ec2.New(session.Must(session.NewSession(awsConfig)))
 105         instanceSet.keys = make(map[string]string)
 106         if instanceSet.ec2config.EBSVolumeType == "" {
 107                 instanceSet.ec2config.EBSVolumeType = "gp2"
 108         }
 109         return instanceSet, nil
 110 }
 111
 112 func awsKeyFingerprint(pk ssh.PublicKey) (md5fp string, sha1fp string, err error) {
 113         // AWS key fingerprints don't use the usual key fingerprint
 114         // you get from ssh-keygen or ssh.FingerprintLegacyMD5()
 115         // (you can get that from md5.Sum(pk.Marshal())
 116         //
 117         // AWS uses the md5 or sha1 of the PKIX DER encoding of the
 118         // public key, so calculate those fingerprints here.
 119         var rsaPub struct {
 120                 Name string
 121                 E    *big.Int
 122                 N    *big.Int
 123         }
 124         if err := ssh.Unmarshal(pk.Marshal(), &rsaPub); err != nil {
 125                 return "", "", fmt.Errorf("agent: Unmarshal failed to parse public key: %v", err)
 126         }
 127         rsaPk := rsa.PublicKey{
 128                 E: int(rsaPub.E.Int64()),
 129                 N: rsaPub.N,
 130         }
 131         pkix, _ := x509.MarshalPKIXPublicKey(&rsaPk)
 132         md5pkix := md5.Sum([]byte(pkix))
 133         sha1pkix := sha1.Sum([]byte(pkix))
 134         md5fp = ""
 135         sha1fp = ""
 136         for i := 0; i < len(md5pkix); i++ {
 137                 md5fp += fmt.Sprintf(":%02x", md5pkix[i])
 138         }
 139         for i := 0; i < len(sha1pkix); i++ {
 140                 sha1fp += fmt.Sprintf(":%02x", sha1pkix[i])
 141         }
 142         return md5fp[1:], sha1fp[1:], nil
 143 }
 144
 145 func (instanceSet *ec2InstanceSet) Create(
 146         instanceType arvados.InstanceType,
 147         imageID cloud.ImageID,
 148         newTags cloud.InstanceTags,
 149         initCommand cloud.InitCommand,
 150         publicKey ssh.PublicKey) (cloud.Instance, error) {
 151
 152         md5keyFingerprint, sha1keyFingerprint, err := awsKeyFingerprint(publicKey)
 153         if err != nil {
 154                 return nil, fmt.Errorf("Could not make key fingerprint: %v", err)
 155         }
 156         instanceSet.keysMtx.Lock()
 157         var keyname string
 158         var ok bool
 159         if keyname, ok = instanceSet.keys[md5keyFingerprint]; !ok {
 160                 keyout, err := instanceSet.client.DescribeKeyPairs(&ec2.DescribeKeyPairsInput{
 161                         Filters: []*ec2.Filter{{
 162                                 Name:   aws.String("fingerprint"),
 163                                 Values: []*string{&md5keyFingerprint, &sha1keyFingerprint},
 164                         }},
 165                 })
 166                 if err != nil {
 167                         return nil, fmt.Errorf("Could not search for keypair: %v", err)
 168                 }
 169
 170                 if len(keyout.KeyPairs) > 0 {
 171                         keyname = *(keyout.KeyPairs[0].KeyName)
 172                 } else {
 173                         keyname = "arvados-dispatch-keypair-" + md5keyFingerprint
 174                         _, err := instanceSet.client.ImportKeyPair(&ec2.ImportKeyPairInput{
 175                                 KeyName:           &keyname,
 176                                 PublicKeyMaterial: ssh.MarshalAuthorizedKey(publicKey),
 177                         })
 178                         if err != nil {
 179                                 return nil, fmt.Errorf("Could not import keypair: %v", err)
 180                         }
 181                 }
 182                 instanceSet.keys[md5keyFingerprint] = keyname
 183         }
 184         instanceSet.keysMtx.Unlock()
 185
 186         ec2tags := []*ec2.Tag{}
 187         for k, v := range newTags {
 188                 ec2tags = append(ec2tags, &ec2.Tag{
 189                         Key:   aws.String(k),
 190                         Value: aws.String(v),
 191                 })
 192         }
 193
 194         var groups []string
 195         for sg := range instanceSet.ec2config.SecurityGroupIDs {
 196                 groups = append(groups, sg)
 197         }
 198
 199         rii := ec2.RunInstancesInput{
 200                 ImageId:      aws.String(string(imageID)),
 201                 InstanceType: &instanceType.ProviderType,
 202                 MaxCount:     aws.Int64(1),
 203                 MinCount:     aws.Int64(1),
 204                 KeyName:      &keyname,
 205
 206                 NetworkInterfaces: []*ec2.InstanceNetworkInterfaceSpecification{
 207                         {
 208                                 AssociatePublicIpAddress: aws.Bool(false),
 209                                 DeleteOnTermination:      aws.Bool(true),
 210                                 DeviceIndex:              aws.Int64(0),
 211                                 Groups:                   aws.StringSlice(groups),
 212                                 SubnetId:                 &instanceSet.ec2config.SubnetID,
 213                         }},
 214                 DisableApiTermination:             aws.Bool(false),
 215                 InstanceInitiatedShutdownBehavior: aws.String("terminate"),
 216                 TagSpecifications: []*ec2.TagSpecification{
 217                         {
 218                                 ResourceType: aws.String("instance"),
 219                                 Tags:         ec2tags,
 220                         }},
 221                 UserData: aws.String(base64.StdEncoding.EncodeToString([]byte("#!/bin/sh\n" + initCommand + "\n"))),
 222         }
 223
 224         if instanceType.AddedScratch > 0 {
 225                 rii.BlockDeviceMappings = []*ec2.BlockDeviceMapping{{
 226                         DeviceName: aws.String("/dev/xvdt"),
 227                         Ebs: &ec2.EbsBlockDevice{
 228                                 DeleteOnTermination: aws.Bool(true),
 229                                 VolumeSize:          aws.Int64((int64(instanceType.AddedScratch) + (1<<30 - 1)) >> 30),
 230                                 VolumeType:          &instanceSet.ec2config.EBSVolumeType,
 231                         }}}
 232         }
 233
 234         if instanceType.Preemptible {
 235                 rii.InstanceMarketOptions = &ec2.InstanceMarketOptionsRequest{
 236                         MarketType: aws.String("spot"),
 237                         SpotOptions: &ec2.SpotMarketOptions{
 238                                 InstanceInterruptionBehavior: aws.String("terminate"),
 239                                 MaxPrice:                     aws.String(fmt.Sprintf("%v", instanceType.Price)),
 240                         }}
 241         }
 242
 243         if instanceSet.ec2config.IAMInstanceProfile != "" {
 244                 rii.IamInstanceProfile = &ec2.IamInstanceProfileSpecification{
 245                         Name: aws.String(instanceSet.ec2config.IAMInstanceProfile),
 246                 }
 247         }
 248
 249         rsv, err := instanceSet.client.RunInstances(&rii)
 250         err = wrapError(err, &instanceSet.throttleDelayCreate)
 251         if err != nil {
 252                 return nil, err
 253         }
 254         return &ec2Instance{
 255                 provider: instanceSet,
 256                 instance: rsv.Instances[0],
 257         }, nil
 258 }
 259
 260 func (instanceSet *ec2InstanceSet) Instances(tags cloud.InstanceTags) (instances []cloud.Instance, err error) {
 261         var filters []*ec2.Filter
 262         for k, v := range tags {
 263                 filters = append(filters, &ec2.Filter{
 264                         Name:   aws.String("tag:" + k),
 265                         Values: []*string{aws.String(v)},
 266                 })
 267         }
 268         needAZs := false
 269         dii := &ec2.DescribeInstancesInput{Filters: filters}
 270         for {
 271                 dio, err := instanceSet.client.DescribeInstances(dii)
 272                 err = wrapError(err, &instanceSet.throttleDelayInstances)
 273                 if err != nil {
 274                         return nil, err
 275                 }
 276
 277                 for _, rsv := range dio.Reservations {
 278                         for _, inst := range rsv.Instances {
 279                                 if *inst.State.Name != "shutting-down" && *inst.State.Name != "terminated" {
 280                                         instances = append(instances, &ec2Instance{
 281                                                 provider: instanceSet,
 282                                                 instance: inst,
 283                                         })
 284                                         if aws.StringValue(inst.InstanceLifecycle) == "spot" {
 285                                                 needAZs = true
 286                                         }
 287                                 }
 288                         }
 289                 }
 290                 if dio.NextToken == nil {
 291                         break
 292                 }
 293                 dii.NextToken = dio.NextToken
 294         }
 295         if needAZs && instanceSet.ec2config.SpotPriceUpdateInterval > 0 {
 296                 az := map[string]string{}
 297                 err := instanceSet.client.DescribeInstanceStatusPages(&ec2.DescribeInstanceStatusInput{
 298                         IncludeAllInstances: aws.Bool(true),
 299                 }, func(page *ec2.DescribeInstanceStatusOutput, lastPage bool) bool {
 300                         for _, ent := range page.InstanceStatuses {
 301                                 az[*ent.InstanceId] = *ent.AvailabilityZone
 302                         }
 303                         return true
 304                 })
 305                 if err != nil {
 306                         instanceSet.logger.Warnf("error getting instance statuses: %s", err)
 307                 }
 308                 for _, inst := range instances {
 309                         inst := inst.(*ec2Instance)
 310                         inst.availabilityZone = az[*inst.instance.InstanceId]
 311                 }
 312                 instanceSet.updateSpotPrices(instances)
 313         }
 314         return instances, err
 315 }
 316
 317 type priceKey struct {
 318         instanceType     string
 319         spot             bool
 320         availabilityZone string
 321 }
 322
 323 // Refresh recent spot instance pricing data for the given instances,
 324 // unless we already have recent pricing data for all relevant types.
 325 func (instanceSet *ec2InstanceSet) updateSpotPrices(instances []cloud.Instance) {
 326         if len(instances) == 0 {
 327                 return
 328         }
 329
 330         instanceSet.pricesLock.Lock()
 331         defer instanceSet.pricesLock.Unlock()
 332         if instanceSet.prices == nil {
 333                 instanceSet.prices = map[priceKey][]cloud.InstancePrice{}
 334                 instanceSet.pricesUpdated = map[priceKey]time.Time{}
 335         }
 336
 337         updateTime := time.Now()
 338         staleTime := updateTime.Add(-instanceSet.ec2config.SpotPriceUpdateInterval.Duration())
 339         needUpdate := false
 340         allTypes := map[string]bool{}
 341
 342         for _, inst := range instances {
 343                 ec2inst := inst.(*ec2Instance).instance
 344                 if aws.StringValue(ec2inst.InstanceLifecycle) == "spot" {
 345                         pk := priceKey{
 346                                 instanceType:     *ec2inst.InstanceType,
 347                                 spot:             true,
 348                                 availabilityZone: inst.(*ec2Instance).availabilityZone,
 349                         }
 350                         if instanceSet.pricesUpdated[pk].Before(staleTime) {
 351                                 needUpdate = true
 352                         }
 353                         allTypes[*ec2inst.InstanceType] = true
 354                 }
 355         }
 356         if !needUpdate {
 357                 return
 358         }
 359         var typeFilterValues []*string
 360         for instanceType := range allTypes {
 361                 typeFilterValues = append(typeFilterValues, aws.String(instanceType))
 362         }
 363         // Get 3x update interval worth of pricing data. (Ideally the
 364         // AWS API would tell us "we have shown you all of the price
 365         // changes up to time T", but it doesn't, so we'll just ask
 366         // for 3 intervals worth of data on each update, de-duplicate
 367         // the data points, and not worry too much about occasionally
 368         // missing some data points when our lookups fail twice in a
 369         // row.
 370         dsphi := &ec2.DescribeSpotPriceHistoryInput{
 371                 StartTime: aws.Time(updateTime.Add(-3 * instanceSet.ec2config.SpotPriceUpdateInterval.Duration())),
 372                 Filters: []*ec2.Filter{
 373                         &ec2.Filter{Name: aws.String("instance-type"), Values: typeFilterValues},
 374                         &ec2.Filter{Name: aws.String("product-description"), Values: []*string{aws.String("Linux/UNIX")}},
 375                 },
 376         }
 377         err := instanceSet.client.DescribeSpotPriceHistoryPages(dsphi, func(page *ec2.DescribeSpotPriceHistoryOutput, lastPage bool) bool {
 378                 for _, ent := range page.SpotPriceHistory {
 379                         if ent.InstanceType == nil || ent.SpotPrice == nil || ent.Timestamp == nil {
 380                                 // bogus record?
 381                                 continue
 382                         }
 383                         price, err := strconv.ParseFloat(*ent.SpotPrice, 64)
 384                         if err != nil {
 385                                 // bogus record?
 386                                 continue
 387                         }
 388                         pk := priceKey{
 389                                 instanceType:     *ent.InstanceType,
 390                                 spot:             true,
 391                                 availabilityZone: *ent.AvailabilityZone,
 392                         }
 393                         instanceSet.prices[pk] = append(instanceSet.prices[pk], cloud.InstancePrice{
 394                                 StartTime: *ent.Timestamp,
 395                                 Price:     price,
 396                         })
 397                         instanceSet.pricesUpdated[pk] = updateTime
 398                 }
 399                 return true
 400         })
 401         if err != nil {
 402                 instanceSet.logger.Warnf("error retrieving spot instance prices: %s", err)
 403         }
 404
 405         expiredTime := updateTime.Add(-64 * instanceSet.ec2config.SpotPriceUpdateInterval.Duration())
 406         for pk, last := range instanceSet.pricesUpdated {
 407                 if last.Before(expiredTime) {
 408                         delete(instanceSet.pricesUpdated, pk)
 409                         delete(instanceSet.prices, pk)
 410                 }
 411         }
 412         for pk, prices := range instanceSet.prices {
 413                 instanceSet.prices[pk] = cloud.NormalizePriceHistory(prices)
 414         }
 415 }
 416
 417 func (instanceSet *ec2InstanceSet) Stop() {
 418 }
 419
 420 type ec2Instance struct {
 421         provider         *ec2InstanceSet
 422         instance         *ec2.Instance
 423         availabilityZone string // sometimes available for spot instances
 424 }
 425
 426 func (inst *ec2Instance) ID() cloud.InstanceID {
 427         return cloud.InstanceID(*inst.instance.InstanceId)
 428 }
 429
 430 func (inst *ec2Instance) String() string {
 431         return *inst.instance.InstanceId
 432 }
 433
 434 func (inst *ec2Instance) ProviderType() string {
 435         return *inst.instance.InstanceType
 436 }
 437
 438 func (inst *ec2Instance) SetTags(newTags cloud.InstanceTags) error {
 439         var ec2tags []*ec2.Tag
 440         for k, v := range newTags {
 441                 ec2tags = append(ec2tags, &ec2.Tag{
 442                         Key:   aws.String(k),
 443                         Value: aws.String(v),
 444                 })
 445         }
 446
 447         _, err := inst.provider.client.CreateTags(&ec2.CreateTagsInput{
 448                 Resources: []*string{inst.instance.InstanceId},
 449                 Tags:      ec2tags,
 450         })
 451
 452         return err
 453 }
 454
 455 func (inst *ec2Instance) Tags() cloud.InstanceTags {
 456         tags := make(map[string]string)
 457
 458         for _, t := range inst.instance.Tags {
 459                 tags[*t.Key] = *t.Value
 460         }
 461
 462         return tags
 463 }
 464
 465 func (inst *ec2Instance) Destroy() error {
 466         _, err := inst.provider.client.TerminateInstances(&ec2.TerminateInstancesInput{
 467                 InstanceIds: []*string{inst.instance.InstanceId},
 468         })
 469         return err
 470 }
 471
 472 func (inst *ec2Instance) Address() string {
 473         if inst.instance.PrivateIpAddress != nil {
 474                 return *inst.instance.PrivateIpAddress
 475         }
 476         return ""
 477 }
 478
 479 func (inst *ec2Instance) RemoteUser() string {
 480         return inst.provider.ec2config.AdminUsername
 481 }
 482
 483 func (inst *ec2Instance) VerifyHostKey(ssh.PublicKey, *ssh.Client) error {
 484         return cloud.ErrNotImplemented
 485 }
 486
 487 // PriceHistory returns the price history for this specific instance.
 488 //
 489 // AWS documentation is elusive about whether the hourly cost of a
 490 // given spot instance changes as the current spot price changes for
 491 // the corresponding instance type and availability zone. Our
 492 // implementation assumes the answer is yes, based on the following
 493 // hints.
 494 //
 495 // https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/spot-requests.html
 496 // says: "After your Spot Instance is running, if the Spot price rises
 497 // above your maximum price, Amazon EC2 interrupts your Spot
 498 // Instance." (This doesn't address what happens when the spot price
 499 // rises *without* exceeding your maximum price.)
 500 //
 501 // https://docs.aws.amazon.com/whitepapers/latest/cost-optimization-leveraging-ec2-spot-instances/how-spot-instances-work.html
 502 // says: "You pay the Spot price that's in effect, billed to the
 503 // nearest second." (But it's not explicitly stated whether "the price
 504 // in effect" changes over time for a given instance.)
 505 //
 506 // The same page also says, in a discussion about the effect of
 507 // specifying a maximum price: "Note that you never pay more than the
 508 // Spot price that is in effect when your Spot Instance is running."
 509 // (The use of the phrase "is running", as opposed to "was launched",
 510 // hints that pricing is dynamic.)
 511 func (inst *ec2Instance) PriceHistory(instType arvados.InstanceType) []cloud.InstancePrice {
 512         inst.provider.pricesLock.Lock()
 513         defer inst.provider.pricesLock.Unlock()
 514         // Note updateSpotPrices currently populates
 515         // inst.provider.prices only for spot instances, so if
 516         // spot==false here, we will return no data.
 517         pk := priceKey{
 518                 instanceType:     *inst.instance.InstanceType,
 519                 spot:             aws.StringValue(inst.instance.InstanceLifecycle) == "spot",
 520                 availabilityZone: inst.availabilityZone,
 521         }
 522         var prices []cloud.InstancePrice
 523         for _, price := range inst.provider.prices[pk] {
 524                 // ceil(added scratch space in GiB)
 525                 gib := (instType.AddedScratch + 1<<30 - 1) >> 30
 526                 monthly := inst.provider.ec2config.EBSPrice * float64(gib)
 527                 hourly := monthly / 30 / 24
 528                 price.Price += hourly
 529                 prices = append(prices, price)
 530         }
 531         return prices
 532 }
 533
 534 type rateLimitError struct {
 535         error
 536         earliestRetry time.Time
 537 }
 538
 539 func (err rateLimitError) EarliestRetry() time.Time {
 540         return err.earliestRetry
 541 }
 542
 543 var isCodeCapacity = map[string]bool{
 544         "InsufficientFreeAddressesInSubnet": true,
 545         "InsufficientInstanceCapacity":      true,
 546         "InsufficientVolumeCapacity":        true,
 547         "MaxSpotInstanceCountExceeded":      true,
 548         "VcpuLimitExceeded":                 true,
 549 }
 550
 551 // isErrorCapacity returns whether the error is to be throttled based on its code.
 552 // Returns false if error is nil.
 553 func isErrorCapacity(err error) bool {
 554         if aerr, ok := err.(awserr.Error); ok && aerr != nil {
 555                 if _, ok := isCodeCapacity[aerr.Code()]; ok {
 556                         return true
 557                 }
 558         }
 559         return false
 560 }
 561
 562 type ec2QuotaError struct {
 563         error
 564 }
 565
 566 func (er *ec2QuotaError) IsQuotaError() bool {
 567         return true
 568 }
 569
 570 func wrapError(err error, throttleValue *atomic.Value) error {
 571         if request.IsErrorThrottle(err) {
 572                 // Back off exponentially until an upstream call
 573                 // either succeeds or returns a non-throttle error.
 574                 d, _ := throttleValue.Load().(time.Duration)
 575                 d = d*3/2 + time.Second
 576                 if d < throttleDelayMin {
 577                         d = throttleDelayMin
 578                 } else if d > throttleDelayMax {
 579                         d = throttleDelayMax
 580                 }
 581                 throttleValue.Store(d)
 582                 return rateLimitError{error: err, earliestRetry: time.Now().Add(d)}
 583         } else if isErrorCapacity(err) {
 584                 return &ec2QuotaError{err}
 585         } else if err != nil {
 586                 throttleValue.Store(time.Duration(0))
 587                 return err
 588         }
 589         throttleValue.Store(time.Duration(0))
 590         return nil
 591 }