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         keyname, err := instanceSet.getKeyName(publicKey)
 153         if err != nil {
 154                 return nil, err
 155         }
 156
 157         ec2tags := []*ec2.Tag{}
 158         for k, v := range newTags {
 159                 ec2tags = append(ec2tags, &ec2.Tag{
 160                         Key:   aws.String(k),
 161                         Value: aws.String(v),
 162                 })
 163         }
 164
 165         var groups []string
 166         for sg := range instanceSet.ec2config.SecurityGroupIDs {
 167                 groups = append(groups, sg)
 168         }
 169
 170         rii := ec2.RunInstancesInput{
 171                 ImageId:      aws.String(string(imageID)),
 172                 InstanceType: &instanceType.ProviderType,
 173                 MaxCount:     aws.Int64(1),
 174                 MinCount:     aws.Int64(1),
 175                 KeyName:      &keyname,
 176
 177                 NetworkInterfaces: []*ec2.InstanceNetworkInterfaceSpecification{
 178                         {
 179                                 AssociatePublicIpAddress: aws.Bool(false),
 180                                 DeleteOnTermination:      aws.Bool(true),
 181                                 DeviceIndex:              aws.Int64(0),
 182                                 Groups:                   aws.StringSlice(groups),
 183                                 SubnetId:                 &instanceSet.ec2config.SubnetID,
 184                         }},
 185                 DisableApiTermination:             aws.Bool(false),
 186                 InstanceInitiatedShutdownBehavior: aws.String("terminate"),
 187                 TagSpecifications: []*ec2.TagSpecification{
 188                         {
 189                                 ResourceType: aws.String("instance"),
 190                                 Tags:         ec2tags,
 191                         }},
 192                 UserData: aws.String(base64.StdEncoding.EncodeToString([]byte("#!/bin/sh\n" + initCommand + "\n"))),
 193         }
 194
 195         if instanceType.AddedScratch > 0 {
 196                 rii.BlockDeviceMappings = []*ec2.BlockDeviceMapping{{
 197                         DeviceName: aws.String("/dev/xvdt"),
 198                         Ebs: &ec2.EbsBlockDevice{
 199                                 DeleteOnTermination: aws.Bool(true),
 200                                 VolumeSize:          aws.Int64((int64(instanceType.AddedScratch) + (1<<30 - 1)) >> 30),
 201                                 VolumeType:          &instanceSet.ec2config.EBSVolumeType,
 202                         }}}
 203         }
 204
 205         if instanceType.Preemptible {
 206                 rii.InstanceMarketOptions = &ec2.InstanceMarketOptionsRequest{
 207                         MarketType: aws.String("spot"),
 208                         SpotOptions: &ec2.SpotMarketOptions{
 209                                 InstanceInterruptionBehavior: aws.String("terminate"),
 210                                 MaxPrice:                     aws.String(fmt.Sprintf("%v", instanceType.Price)),
 211                         }}
 212         }
 213
 214         if instanceSet.ec2config.IAMInstanceProfile != "" {
 215                 rii.IamInstanceProfile = &ec2.IamInstanceProfileSpecification{
 216                         Name: aws.String(instanceSet.ec2config.IAMInstanceProfile),
 217                 }
 218         }
 219
 220         rsv, err := instanceSet.client.RunInstances(&rii)
 221         err = wrapError(err, &instanceSet.throttleDelayCreate)
 222         if err != nil {
 223                 return nil, err
 224         }
 225         return &ec2Instance{
 226                 provider: instanceSet,
 227                 instance: rsv.Instances[0],
 228         }, nil
 229 }
 230
 231 func (instanceSet *ec2InstanceSet) getKeyName(publicKey ssh.PublicKey) (string, error) {
 232         instanceSet.keysMtx.Lock()
 233         defer instanceSet.keysMtx.Unlock()
 234         md5keyFingerprint, sha1keyFingerprint, err := awsKeyFingerprint(publicKey)
 235         if err != nil {
 236                 return "", fmt.Errorf("Could not make key fingerprint: %v", err)
 237         }
 238         if keyname, ok := instanceSet.keys[md5keyFingerprint]; ok {
 239                 return keyname, nil
 240         }
 241         keyout, err := instanceSet.client.DescribeKeyPairs(&ec2.DescribeKeyPairsInput{
 242                 Filters: []*ec2.Filter{{
 243                         Name:   aws.String("fingerprint"),
 244                         Values: []*string{&md5keyFingerprint, &sha1keyFingerprint},
 245                 }},
 246         })
 247         if err != nil {
 248                 return "", fmt.Errorf("Could not search for keypair: %v", err)
 249         }
 250         if len(keyout.KeyPairs) > 0 {
 251                 return *(keyout.KeyPairs[0].KeyName), nil
 252         }
 253         keyname := "arvados-dispatch-keypair-" + md5keyFingerprint
 254         _, err = instanceSet.client.ImportKeyPair(&ec2.ImportKeyPairInput{
 255                 KeyName:           &keyname,
 256                 PublicKeyMaterial: ssh.MarshalAuthorizedKey(publicKey),
 257         })
 258         if err != nil {
 259                 return "", fmt.Errorf("Could not import keypair: %v", err)
 260         }
 261         instanceSet.keys[md5keyFingerprint] = keyname
 262         return keyname, nil
 263 }
 264
 265 func (instanceSet *ec2InstanceSet) Instances(tags cloud.InstanceTags) (instances []cloud.Instance, err error) {
 266         var filters []*ec2.Filter
 267         for k, v := range tags {
 268                 filters = append(filters, &ec2.Filter{
 269                         Name:   aws.String("tag:" + k),
 270                         Values: []*string{aws.String(v)},
 271                 })
 272         }
 273         needAZs := false
 274         dii := &ec2.DescribeInstancesInput{Filters: filters}
 275         for {
 276                 dio, err := instanceSet.client.DescribeInstances(dii)
 277                 err = wrapError(err, &instanceSet.throttleDelayInstances)
 278                 if err != nil {
 279                         return nil, err
 280                 }
 281
 282                 for _, rsv := range dio.Reservations {
 283                         for _, inst := range rsv.Instances {
 284                                 if *inst.State.Name != "shutting-down" && *inst.State.Name != "terminated" {
 285                                         instances = append(instances, &ec2Instance{
 286                                                 provider: instanceSet,
 287                                                 instance: inst,
 288                                         })
 289                                         if aws.StringValue(inst.InstanceLifecycle) == "spot" {
 290                                                 needAZs = true
 291                                         }
 292                                 }
 293                         }
 294                 }
 295                 if dio.NextToken == nil {
 296                         break
 297                 }
 298                 dii.NextToken = dio.NextToken
 299         }
 300         if needAZs && instanceSet.ec2config.SpotPriceUpdateInterval > 0 {
 301                 az := map[string]string{}
 302                 err := instanceSet.client.DescribeInstanceStatusPages(&ec2.DescribeInstanceStatusInput{
 303                         IncludeAllInstances: aws.Bool(true),
 304                 }, func(page *ec2.DescribeInstanceStatusOutput, lastPage bool) bool {
 305                         for _, ent := range page.InstanceStatuses {
 306                                 az[*ent.InstanceId] = *ent.AvailabilityZone
 307                         }
 308                         return true
 309                 })
 310                 if err != nil {
 311                         instanceSet.logger.Warnf("error getting instance statuses: %s", err)
 312                 }
 313                 for _, inst := range instances {
 314                         inst := inst.(*ec2Instance)
 315                         inst.availabilityZone = az[*inst.instance.InstanceId]
 316                 }
 317                 instanceSet.updateSpotPrices(instances)
 318         }
 319         return instances, err
 320 }
 321
 322 type priceKey struct {
 323         instanceType     string
 324         spot             bool
 325         availabilityZone string
 326 }
 327
 328 // Refresh recent spot instance pricing data for the given instances,
 329 // unless we already have recent pricing data for all relevant types.
 330 func (instanceSet *ec2InstanceSet) updateSpotPrices(instances []cloud.Instance) {
 331         if len(instances) == 0 {
 332                 return
 333         }
 334
 335         instanceSet.pricesLock.Lock()
 336         defer instanceSet.pricesLock.Unlock()
 337         if instanceSet.prices == nil {
 338                 instanceSet.prices = map[priceKey][]cloud.InstancePrice{}
 339                 instanceSet.pricesUpdated = map[priceKey]time.Time{}
 340         }
 341
 342         updateTime := time.Now()
 343         staleTime := updateTime.Add(-instanceSet.ec2config.SpotPriceUpdateInterval.Duration())
 344         needUpdate := false
 345         allTypes := map[string]bool{}
 346
 347         for _, inst := range instances {
 348                 ec2inst := inst.(*ec2Instance).instance
 349                 if aws.StringValue(ec2inst.InstanceLifecycle) == "spot" {
 350                         pk := priceKey{
 351                                 instanceType:     *ec2inst.InstanceType,
 352                                 spot:             true,
 353                                 availabilityZone: inst.(*ec2Instance).availabilityZone,
 354                         }
 355                         if instanceSet.pricesUpdated[pk].Before(staleTime) {
 356                                 needUpdate = true
 357                         }
 358                         allTypes[*ec2inst.InstanceType] = true
 359                 }
 360         }
 361         if !needUpdate {
 362                 return
 363         }
 364         var typeFilterValues []*string
 365         for instanceType := range allTypes {
 366                 typeFilterValues = append(typeFilterValues, aws.String(instanceType))
 367         }
 368         // Get 3x update interval worth of pricing data. (Ideally the
 369         // AWS API would tell us "we have shown you all of the price
 370         // changes up to time T", but it doesn't, so we'll just ask
 371         // for 3 intervals worth of data on each update, de-duplicate
 372         // the data points, and not worry too much about occasionally
 373         // missing some data points when our lookups fail twice in a
 374         // row.
 375         dsphi := &ec2.DescribeSpotPriceHistoryInput{
 376                 StartTime: aws.Time(updateTime.Add(-3 * instanceSet.ec2config.SpotPriceUpdateInterval.Duration())),
 377                 Filters: []*ec2.Filter{
 378                         &ec2.Filter{Name: aws.String("instance-type"), Values: typeFilterValues},
 379                         &ec2.Filter{Name: aws.String("product-description"), Values: []*string{aws.String("Linux/UNIX")}},
 380                 },
 381         }
 382         err := instanceSet.client.DescribeSpotPriceHistoryPages(dsphi, func(page *ec2.DescribeSpotPriceHistoryOutput, lastPage bool) bool {
 383                 for _, ent := range page.SpotPriceHistory {
 384                         if ent.InstanceType == nil || ent.SpotPrice == nil || ent.Timestamp == nil {
 385                                 // bogus record?
 386                                 continue
 387                         }
 388                         price, err := strconv.ParseFloat(*ent.SpotPrice, 64)
 389                         if err != nil {
 390                                 // bogus record?
 391                                 continue
 392                         }
 393                         pk := priceKey{
 394                                 instanceType:     *ent.InstanceType,
 395                                 spot:             true,
 396                                 availabilityZone: *ent.AvailabilityZone,
 397                         }
 398                         instanceSet.prices[pk] = append(instanceSet.prices[pk], cloud.InstancePrice{
 399                                 StartTime: *ent.Timestamp,
 400                                 Price:     price,
 401                         })
 402                         instanceSet.pricesUpdated[pk] = updateTime
 403                 }
 404                 return true
 405         })
 406         if err != nil {
 407                 instanceSet.logger.Warnf("error retrieving spot instance prices: %s", err)
 408         }
 409
 410         expiredTime := updateTime.Add(-64 * instanceSet.ec2config.SpotPriceUpdateInterval.Duration())
 411         for pk, last := range instanceSet.pricesUpdated {
 412                 if last.Before(expiredTime) {
 413                         delete(instanceSet.pricesUpdated, pk)
 414                         delete(instanceSet.prices, pk)
 415                 }
 416         }
 417         for pk, prices := range instanceSet.prices {
 418                 instanceSet.prices[pk] = cloud.NormalizePriceHistory(prices)
 419         }
 420 }
 421
 422 func (instanceSet *ec2InstanceSet) Stop() {
 423 }
 424
 425 type ec2Instance struct {
 426         provider         *ec2InstanceSet
 427         instance         *ec2.Instance
 428         availabilityZone string // sometimes available for spot instances
 429 }
 430
 431 func (inst *ec2Instance) ID() cloud.InstanceID {
 432         return cloud.InstanceID(*inst.instance.InstanceId)
 433 }
 434
 435 func (inst *ec2Instance) String() string {
 436         return *inst.instance.InstanceId
 437 }
 438
 439 func (inst *ec2Instance) ProviderType() string {
 440         return *inst.instance.InstanceType
 441 }
 442
 443 func (inst *ec2Instance) SetTags(newTags cloud.InstanceTags) error {
 444         var ec2tags []*ec2.Tag
 445         for k, v := range newTags {
 446                 ec2tags = append(ec2tags, &ec2.Tag{
 447                         Key:   aws.String(k),
 448                         Value: aws.String(v),
 449                 })
 450         }
 451
 452         _, err := inst.provider.client.CreateTags(&ec2.CreateTagsInput{
 453                 Resources: []*string{inst.instance.InstanceId},
 454                 Tags:      ec2tags,
 455         })
 456
 457         return err
 458 }
 459
 460 func (inst *ec2Instance) Tags() cloud.InstanceTags {
 461         tags := make(map[string]string)
 462
 463         for _, t := range inst.instance.Tags {
 464                 tags[*t.Key] = *t.Value
 465         }
 466
 467         return tags
 468 }
 469
 470 func (inst *ec2Instance) Destroy() error {
 471         _, err := inst.provider.client.TerminateInstances(&ec2.TerminateInstancesInput{
 472                 InstanceIds: []*string{inst.instance.InstanceId},
 473         })
 474         return err
 475 }
 476
 477 func (inst *ec2Instance) Address() string {
 478         if inst.instance.PrivateIpAddress != nil {
 479                 return *inst.instance.PrivateIpAddress
 480         }
 481         return ""
 482 }
 483
 484 func (inst *ec2Instance) RemoteUser() string {
 485         return inst.provider.ec2config.AdminUsername
 486 }
 487
 488 func (inst *ec2Instance) VerifyHostKey(ssh.PublicKey, *ssh.Client) error {
 489         return cloud.ErrNotImplemented
 490 }
 491
 492 // PriceHistory returns the price history for this specific instance.
 493 //
 494 // AWS documentation is elusive about whether the hourly cost of a
 495 // given spot instance changes as the current spot price changes for
 496 // the corresponding instance type and availability zone. Our
 497 // implementation assumes the answer is yes, based on the following
 498 // hints.
 499 //
 500 // https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/spot-requests.html
 501 // says: "After your Spot Instance is running, if the Spot price rises
 502 // above your maximum price, Amazon EC2 interrupts your Spot
 503 // Instance." (This doesn't address what happens when the spot price
 504 // rises *without* exceeding your maximum price.)
 505 //
 506 // https://docs.aws.amazon.com/whitepapers/latest/cost-optimization-leveraging-ec2-spot-instances/how-spot-instances-work.html
 507 // says: "You pay the Spot price that's in effect, billed to the
 508 // nearest second." (But it's not explicitly stated whether "the price
 509 // in effect" changes over time for a given instance.)
 510 //
 511 // The same page also says, in a discussion about the effect of
 512 // specifying a maximum price: "Note that you never pay more than the
 513 // Spot price that is in effect when your Spot Instance is running."
 514 // (The use of the phrase "is running", as opposed to "was launched",
 515 // hints that pricing is dynamic.)
 516 func (inst *ec2Instance) PriceHistory(instType arvados.InstanceType) []cloud.InstancePrice {
 517         inst.provider.pricesLock.Lock()
 518         defer inst.provider.pricesLock.Unlock()
 519         // Note updateSpotPrices currently populates
 520         // inst.provider.prices only for spot instances, so if
 521         // spot==false here, we will return no data.
 522         pk := priceKey{
 523                 instanceType:     *inst.instance.InstanceType,
 524                 spot:             aws.StringValue(inst.instance.InstanceLifecycle) == "spot",
 525                 availabilityZone: inst.availabilityZone,
 526         }
 527         var prices []cloud.InstancePrice
 528         for _, price := range inst.provider.prices[pk] {
 529                 // ceil(added scratch space in GiB)
 530                 gib := (instType.AddedScratch + 1<<30 - 1) >> 30
 531                 monthly := inst.provider.ec2config.EBSPrice * float64(gib)
 532                 hourly := monthly / 30 / 24
 533                 price.Price += hourly
 534                 prices = append(prices, price)
 535         }
 536         return prices
 537 }
 538
 539 type rateLimitError struct {
 540         error
 541         earliestRetry time.Time
 542 }
 543
 544 func (err rateLimitError) EarliestRetry() time.Time {
 545         return err.earliestRetry
 546 }
 547
 548 var isCodeCapacity = map[string]bool{
 549         "InsufficientFreeAddressesInSubnet": true,
 550         "InsufficientInstanceCapacity":      true,
 551         "InsufficientVolumeCapacity":        true,
 552         "MaxSpotInstanceCountExceeded":      true,
 553         "VcpuLimitExceeded":                 true,
 554 }
 555
 556 // isErrorCapacity returns whether the error is to be throttled based on its code.
 557 // Returns false if error is nil.
 558 func isErrorCapacity(err error) bool {
 559         if aerr, ok := err.(awserr.Error); ok && aerr != nil {
 560                 if _, ok := isCodeCapacity[aerr.Code()]; ok {
 561                         return true
 562                 }
 563         }
 564         return false
 565 }
 566
 567 type ec2QuotaError struct {
 568         error
 569 }
 570
 571 func (er *ec2QuotaError) IsQuotaError() bool {
 572         return true
 573 }
 574
 575 func wrapError(err error, throttleValue *atomic.Value) error {
 576         if request.IsErrorThrottle(err) {
 577                 // Back off exponentially until an upstream call
 578                 // either succeeds or returns a non-throttle error.
 579                 d, _ := throttleValue.Load().(time.Duration)
 580                 d = d*3/2 + time.Second
 581                 if d < throttleDelayMin {
 582                         d = throttleDelayMin
 583                 } else if d > throttleDelayMax {
 584                         d = throttleDelayMax
 585                 }
 586                 throttleValue.Store(d)
 587                 return rateLimitError{error: err, earliestRetry: time.Now().Add(d)}
 588         } else if isErrorCapacity(err) {
 589                 return &ec2QuotaError{err}
 590         } else if err != nil {
 591                 throttleValue.Store(time.Duration(0))
 592                 return err
 593         }
 594         throttleValue.Store(time.Duration(0))
 595         return nil
 596 }