internal/coordinator/pool/ec2.go - build - Git at Google

 // Copyright 2020 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.

 // +build go1.13
 // +build linux darwin

 package pool

 import (
 	"context"
 	"errors"
 	"fmt"
 	"html"
 	"io"
 	"log"
 	"sync"
 	"time"

 	"golang.org/x/build/buildenv"
 	"golang.org/x/build/buildlet"
 	"golang.org/x/build/dashboard"
 	"golang.org/x/build/internal/cloud"
 	"golang.org/x/build/internal/spanlog"
 )

 var _ Buildlet = (*EC2Buildlet)(nil)

 // ec2Buildlet is the package level buildlet pool.
 //
 // TODO(golang.org/issues/38337) remove once a package level variable is no longer
 // required by the main package.
 var ec2Buildlet *EC2Buildlet

 // EC2BuildetPool retrieves the package level EC2Buildlet pool set by the constructor.
 //
 // TODO(golang.org/issues/38337) remove once a package level variable is no longer
 // required by the main package.
 func EC2BuildetPool() *EC2Buildlet {
 	return ec2Buildlet
 }

 func init() {
 	// initializes a basic package level ec2Buildlet pool to enable basic testing in other
 	// packages.
 	//
 	// TODO(golang.org/issues/38337) remove once a package level variable is no longer
 	// required by the main package.
 	ec2Buildlet = &EC2Buildlet{
 		ledger: newLedger(),
 	}
 }

 // awsClient represents the aws client used to interact with AWS. This is a partial
 // implementation of pool.AWSClient.
 type awsClient interface {
 	DestroyInstances(ctx context.Context, instIDs ...string) error
 	Quota(ctx context.Context, service, code string) (int64, error)
 	InstanceTypesARM(ctx context.Context) ([]*cloud.InstanceType, error)
 	RunningInstances(ctx context.Context) ([]*cloud.Instance, error)
 }

 // EC2Opt is optional configuration for the the buildlet.
 type EC2Opt func(*EC2Buildlet)

 // WithVMDeleteTimeout sets the VM deletion timeout for all EC2 VMs.
 func WithVMDeleteTimeout(timeout time.Duration) EC2Opt {
 	return func(eb *EC2Buildlet) {
 		eb.vmDeleteTimeout = timeout
 	}
 }

 // EC2Buildlet manages a pool of AWS EC2 buildlets.
 type EC2Buildlet struct {
 	once sync.Once
 	// done channel closing will signal the pollers to discontinue polling
 	done chan struct{}

 	// awsClient is the client used to interact with AWS services.
 	awsClient awsClient
 	// buildEnv contains the build enviornment settings.
 	buildEnv *buildenv.Environment
 	// buildletClient is the client used to create a buildlet.
 	buildletClient ec2BuildletClient
 	// hosts provides the host configuration for all hosts. It is passed in to facilitate
 	// testing.
 	hosts map[string]*dashboard.HostConfig
 	// isRemoteBuildletFunc informs the caller is a VM instance is being used as a remote
 	// buildlet.
 	//
 	// TODO(golang.org/issues/38337) remove once we find a way to pass in remote buildlet
 	// information at the get buidlet request.
 	isRemoteBuildlet IsRemoteBuildletFunc
 	// ledger tracks instances and their resource allocations.
 	ledger *ledger
 	// vmDeleteTimeout contains the timeout used to determine if a VM should be deleted.
 	vmDeleteTimeout time.Duration
 }

 // ec2BuildletClient represents an EC2 buildlet client in the buildlet package.
 type ec2BuildletClient interface {
 	StartNewVM(ctx context.Context, buildEnv *buildenv.Environment, hconf *dashboard.HostConfig, vmName, hostType string, opts *buildlet.VMOpts) (*buildlet.Client, error)
 }

 // NewEC2Buildlet creates a new EC2 buildlet pool used to create and manage the lifecycle of
 // EC2 buildlets. Information about ARM64 instance types is retrieved before starting the pool.
 // EC2 quota types are also retrieved before starting the pool. The pool will continuously poll
 // for quotas which limit the resources that can be consumed by the pool. It will also periodically
 // search for VMs which are no longer in use or are untracked by the pool in order to delete them.
 func NewEC2Buildlet(client *cloud.AWSClient, buildEnv *buildenv.Environment, hosts map[string]*dashboard.HostConfig, fn IsRemoteBuildletFunc, opts ...EC2Opt) (*EC2Buildlet, error) {
 	if fn == nil {
 		return nil, errors.New("remote buildlet check function is not set")
 	}
 	b := &EC2Buildlet{
 		awsClient:        client,
 		buildEnv:         buildEnv,
 		buildletClient:   buildlet.NewEC2Client(client),
 		done:             make(chan struct{}),
 		hosts:            hosts,
 		isRemoteBuildlet: fn,
 		ledger:           newLedger(),
 		vmDeleteTimeout:  45 * time.Minute, // default VM delete timeout
 	}
 	for _, opt := range opts {
 		opt(b)
 	}
 	if err := b.retrieveAndSetQuota(); err != nil {
 		return nil, fmt.Errorf("unable to create EC2 pool: %w", err)
 	}
 	if err := b.retrieveAndSetInstanceTypes(); err != nil {
 		return nil, fmt.Errorf("unable to create EC2 pool: %w", err)
 	}
 	go b.cleanupUnusedVMs()
 	go b.pollQuota()

 	// TODO(golang.org/issues/38337) remove once a package level variable is no longer
 	// required by the main package.
 	ec2Buildlet = b
 	return b, nil
 }

 // GetBuildlet retrieves a buildlet client for a newly created buildlet.
 func (eb *EC2Buildlet) GetBuildlet(ctx context.Context, hostType string, lg Logger) (*buildlet.Client, error) {
 	hconf, ok := eb.hosts[hostType]
 	if !ok {
 		return nil, fmt.Errorf("ec2 pool: unknown host type %q", hostType)
 	}
 	instName := instanceName(hostType, 7)
 	log.Printf("Creating EC2 VM %q for %s", instName, hostType)
 	kp, err := buildlet.NewKeyPair()
 	if err != nil {
 		log.Printf("failed to create TLS key pair for %s: %s", hostType, err)
 		return nil, fmt.Errorf("failed to create TLS key pair: %w", err)
 	}

 	qsp := lg.CreateSpan("awaiting_ec2_quota")
 	err = eb.ledger.ReserveResources(ctx, instName, hconf.MachineType())
 	qsp.Done(err)
 	if err != nil {
 		return nil, err
 	}

 	ec2BuildletSpan := lg.CreateSpan("create_ec2_buildlet", instName)
 	defer func() { ec2BuildletSpan.Done(err) }()

 	var (
 		createSpan      = lg.CreateSpan("create_ec2_instance", instName)
 		waitBuildlet    spanlog.Span
 		curSpan         = createSpan
 		instanceCreated bool
 	)
 	bc, err := eb.buildletClient.StartNewVM(ctx, eb.buildEnv, hconf, instName, hostType, &buildlet.VMOpts{
 		Zone:     "", // allow the EC2 api pick an availability zone with capacity
 		TLS:      kp,
 		Meta:     make(map[string]string),
 		DeleteIn: deleteTimeoutFromContextOrValue(ctx, eb.vmDeleteTimeout),
 		OnInstanceRequested: func() {
 			log.Printf("EC2 VM %q now booting", instName)
 		},
 		OnInstanceCreated: func() {
 			log.Printf("EC2 VM %q now running", instName)
 			createSpan.Done(nil)
 			instanceCreated = true
 			waitBuildlet = lg.CreateSpan("wait_buildlet_start", instName)
 			curSpan = waitBuildlet
 		},
 		OnGotEC2InstanceInfo: func(inst *cloud.Instance) {
 			lg.LogEventTime("got_instance_info", "waiting_for_buildlet...")
 			eb.ledger.UpdateReservation(instName, inst.ID)
 		},
 	})
 	if err != nil {
 		curSpan.Done(err)
 		log.Printf("EC2 VM creation failed for %s: %v", hostType, err)
 		if instanceCreated {
 			log.Printf("EC2 VM %q failed initialize buildlet client. deleting...", instName)
 			eb.buildletDone(instName)
 		} else {
 			eb.ledger.Remove(instName)
 		}
 		return nil, err
 	}
 	waitBuildlet.Done(nil)
 	bc.SetDescription(fmt.Sprintf("EC2 VM: %s", instName))
 	bc.SetOnHeartbeatFailure(func() {
 		log.Printf("EC2 VM %q failed heartbeat", instName)
 		eb.buildletDone(instName)
 	})
 	return bc, nil
 }

 // String gives a report of capacity usage for the EC2 buildlet pool.
 func (eb *EC2Buildlet) String() string {
 	return fmt.Sprintf("EC2 pool capacity: %s", eb.capacityString())
 }

 // capacityString() gives a report of capacity usage.
 func (eb *EC2Buildlet) capacityString() string {
 	r := eb.ledger.Resources()
 	return fmt.Sprintf("%d instances; %d/%d CPUs", r.InstCount, r.CPUUsed, r.CPULimit)
 }

 // WriteHTMLStatus writes the status of the EC2 buildlet pool to an io.Writer.
 func (eb *EC2Buildlet) WriteHTMLStatus(w io.Writer) {
 	fmt.Fprintf(w, "<b>EC2 pool</b> capacity: %s", eb.capacityString())

 	active := eb.ledger.ResourceTime()
 	if len(active) > 0 {
 		fmt.Fprintf(w, "<ul>")
 		for _, inst := range active {
 			fmt.Fprintf(w, "<li>%v, %s</li>\n", html.EscapeString(inst.Name), friendlyDuration(time.Since(inst.Creation)))
 		}
 		fmt.Fprintf(w, "</ul>")
 	}
 }

 // buildletDone issues a call to destroy the EC2 instance and removes
 // the instance from the ledger. Removing the instance from the ledger
 // also releases any resources allocated to that instance. If an instance
 // is not found in the ledger or on EC2 then an error is logged. All
 // untracked instances will be cleaned up by the polling cleanupUnusedVMs
 // method.
 func (eb *EC2Buildlet) buildletDone(instName string) {
 	vmID := eb.ledger.InstanceID(instName)
 	if vmID == "" {
 		log.Printf("EC2 vm %s not found", instName)
 		return
 	}
 	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 	defer cancel()
 	if err := eb.awsClient.DestroyInstances(ctx, vmID); err != nil {
 		log.Printf("EC2 VM %s deletion failed: %s", instName, err)
 	}
 	eb.ledger.Remove(instName)
 }

 // Close stops the pollers used by the EC2Buildlet pool from running.
 func (eb *EC2Buildlet) Close() {
 	eb.once.Do(func() {
 		close(eb.done)
 	})
 }

 // retrieveAndSetQuota queries EC2 for account relevant quotas and sets the quota in the ledger.
 func (eb *EC2Buildlet) retrieveAndSetQuota() error {
 	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 	defer cancel()

 	cpuQuota, err := eb.awsClient.Quota(ctx, cloud.QuotaServiceEC2, cloud.QuotaCodeCPUOnDemand)
 	if err != nil {
 		log.Printf("unable to query for cpu quota: %s", err)
 		return err
 	}
 	eb.ledger.SetCPULimit(cpuQuota)
 	return nil
 }

 // pollQuota repeatedly polls for the EC2 quota data and sets the quota data in
 // the ledger. It stops polling once the done channel has been closed.
 func (eb *EC2Buildlet) pollQuota() {
 	t := time.NewTicker(time.Hour)
 	defer t.Stop()
 	for {
 		select {
 		case <-t.C:
 			err := eb.retrieveAndSetQuota()
 			if err != nil {
 				log.Printf("polling for EC2 quota failed: %s", err)
 			}
 		case <-eb.done:
 			// closing the done channel signals the end of the polling loop.
 			log.Printf("stopped polling for EC2 quota")
 			return
 		}
 	}
 }

 // retrieveAndSetInstanceTypes retrieves the ARM64 instance types from the EC2
 // service and sets them in the ledger.
 func (eb *EC2Buildlet) retrieveAndSetInstanceTypes() error {
 	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 	defer cancel()

 	its, err := eb.awsClient.InstanceTypesARM(ctx)
 	if err != nil {
 		return fmt.Errorf("unable to retrieve instance types: %w", err)
 	}
 	eb.ledger.UpdateInstanceTypes(its)
 	log.Printf("ec2 buildlet pool instance types updated")
 	return nil
 }

 // cleanupUnusedVMs periodically queries for VMs which are not tracked in the ledger and
 // deletes them. If the done channel has been closed then the polling will exit.
 func (eb *EC2Buildlet) cleanupUnusedVMs() {
 	t := time.NewTicker(2 * time.Minute)
 	defer t.Stop()
 	for {
 		select {
 		case <-t.C:
 			log.Printf("cleaning up unused EC2 instances")
 			eb.destroyUntrackedInstances()
 		case <-eb.done:
 			// closing the done channel signals the end of the polling loop.
 			log.Printf("stopped cleaning up unused EC2 instances")
 			return
 		}
 	}
 }

 // destroyUntrackedInstances searches for VMs which exist but are not being tracked in the
 // ledger and deletes them.
 func (eb *EC2Buildlet) destroyUntrackedInstances() {
 	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
 	defer cancel()

 	insts, err := eb.awsClient.RunningInstances(ctx)
 	if err != nil {
 		log.Printf("failed to query for instances: %s", err)
 		return
 	}
 	deleteInsts := make([]string, 0, len(insts))
 	for _, inst := range insts {
 		if eb.isRemoteBuildlet(inst.Name) {
 			// Remote buildlets have their own expiration mechanism that respects active SSH sessions.
 			log.Printf("destroyUntrackedInstances: skipping remote buildlet %q", inst.Name)
 			continue
 		}
 		if id := eb.ledger.InstanceID(inst.Name); id != "" {
 			continue
 		}
 		deleteInsts = append(deleteInsts, inst.ID)
 		log.Printf("queued for deleting untracked EC2 VM %q with id %q", inst.Name, inst.ID)
 	}
 	if len(deleteInsts) == 0 {
 		return
 	}
 	if err := eb.awsClient.DestroyInstances(ctx, deleteInsts...); err != nil {
 		log.Printf("failed cleaning EC2 VMs: %s", err)
 	}
 }
	// Copyright 2020 The Go Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style
	// license that can be found in the LICENSE file.

	// +build go1.13
	// +build linux darwin

	package pool

	import (
	"context"
	"errors"
	"fmt"
	"html"
	"io"
	"log"
	"sync"
	"time"

	"golang.org/x/build/buildenv"
	"golang.org/x/build/buildlet"
	"golang.org/x/build/dashboard"
	"golang.org/x/build/internal/cloud"
	"golang.org/x/build/internal/spanlog"
	)

	var _ Buildlet = (*EC2Buildlet)(nil)

	// ec2Buildlet is the package level buildlet pool.
	//
	// TODO(golang.org/issues/38337) remove once a package level variable is no longer
	// required by the main package.
	var ec2Buildlet *EC2Buildlet

	// EC2BuildetPool retrieves the package level EC2Buildlet pool set by the constructor.
	//
	// TODO(golang.org/issues/38337) remove once a package level variable is no longer
	// required by the main package.
	func EC2BuildetPool() *EC2Buildlet {
	return ec2Buildlet
	}

	func init() {
	// initializes a basic package level ec2Buildlet pool to enable basic testing in other
	// packages.
	//
	// TODO(golang.org/issues/38337) remove once a package level variable is no longer
	// required by the main package.
	ec2Buildlet = &EC2Buildlet{
	ledger: newLedger(),
	}
	}

	// awsClient represents the aws client used to interact with AWS. This is a partial
	// implementation of pool.AWSClient.
	type awsClient interface {
	DestroyInstances(ctx context.Context, instIDs ...string) error
	Quota(ctx context.Context, service, code string) (int64, error)
	InstanceTypesARM(ctx context.Context) ([]*cloud.InstanceType, error)
	RunningInstances(ctx context.Context) ([]*cloud.Instance, error)
	}

	// EC2Opt is optional configuration for the the buildlet.
	type EC2Opt func(*EC2Buildlet)

	// WithVMDeleteTimeout sets the VM deletion timeout for all EC2 VMs.
	func WithVMDeleteTimeout(timeout time.Duration) EC2Opt {
	return func(eb *EC2Buildlet) {
	eb.vmDeleteTimeout = timeout
	}
	}

	// EC2Buildlet manages a pool of AWS EC2 buildlets.
	type EC2Buildlet struct {
	once sync.Once
	// done channel closing will signal the pollers to discontinue polling
	done chan struct{}

	// awsClient is the client used to interact with AWS services.
	awsClient awsClient
	// buildEnv contains the build enviornment settings.
	buildEnv *buildenv.Environment
	// buildletClient is the client used to create a buildlet.
	buildletClient ec2BuildletClient
	// hosts provides the host configuration for all hosts. It is passed in to facilitate
	// testing.
	hosts map[string]*dashboard.HostConfig
	// isRemoteBuildletFunc informs the caller is a VM instance is being used as a remote
	// buildlet.
	//
	// TODO(golang.org/issues/38337) remove once we find a way to pass in remote buildlet
	// information at the get buidlet request.
	isRemoteBuildlet IsRemoteBuildletFunc
	// ledger tracks instances and their resource allocations.
	ledger *ledger
	// vmDeleteTimeout contains the timeout used to determine if a VM should be deleted.
	vmDeleteTimeout time.Duration
	}

	// ec2BuildletClient represents an EC2 buildlet client in the buildlet package.
	type ec2BuildletClient interface {
	StartNewVM(ctx context.Context, buildEnv buildenv.Environment, hconf dashboard.HostConfig, vmName, hostType string, opts buildlet.VMOpts) (buildlet.Client, error)
	}

	// NewEC2Buildlet creates a new EC2 buildlet pool used to create and manage the lifecycle of
	// EC2 buildlets. Information about ARM64 instance types is retrieved before starting the pool.
	// EC2 quota types are also retrieved before starting the pool. The pool will continuously poll
	// for quotas which limit the resources that can be consumed by the pool. It will also periodically
	// search for VMs which are no longer in use or are untracked by the pool in order to delete them.
	func NewEC2Buildlet(client cloud.AWSClient, buildEnv buildenv.Environment, hosts map[string]dashboard.HostConfig, fn IsRemoteBuildletFunc, opts ...EC2Opt) (EC2Buildlet, error) {
	if fn == nil {
	return nil, errors.New("remote buildlet check function is not set")
	}
	b := &EC2Buildlet{
	awsClient: client,
	buildEnv: buildEnv,
	buildletClient: buildlet.NewEC2Client(client),
	done: make(chan struct{}),
	hosts: hosts,
	isRemoteBuildlet: fn,
	ledger: newLedger(),
	vmDeleteTimeout: 45 * time.Minute, // default VM delete timeout
	}
	for _, opt := range opts {
	opt(b)
	}
	if err := b.retrieveAndSetQuota(); err != nil {
	return nil, fmt.Errorf("unable to create EC2 pool: %w", err)
	}
	if err := b.retrieveAndSetInstanceTypes(); err != nil {
	return nil, fmt.Errorf("unable to create EC2 pool: %w", err)
	}
	go b.cleanupUnusedVMs()
	go b.pollQuota()

	// TODO(golang.org/issues/38337) remove once a package level variable is no longer
	// required by the main package.
	ec2Buildlet = b
	return b, nil
	}

	// GetBuildlet retrieves a buildlet client for a newly created buildlet.
	func (eb EC2Buildlet) GetBuildlet(ctx context.Context, hostType string, lg Logger) (buildlet.Client, error) {
	hconf, ok := eb.hosts[hostType]
	if !ok {
	return nil, fmt.Errorf("ec2 pool: unknown host type %q", hostType)
	}
	instName := instanceName(hostType, 7)
	log.Printf("Creating EC2 VM %q for %s", instName, hostType)
	kp, err := buildlet.NewKeyPair()
	if err != nil {
	log.Printf("failed to create TLS key pair for %s: %s", hostType, err)
	return nil, fmt.Errorf("failed to create TLS key pair: %w", err)
	}

	qsp := lg.CreateSpan("awaiting_ec2_quota")
	err = eb.ledger.ReserveResources(ctx, instName, hconf.MachineType())
	qsp.Done(err)
	if err != nil {
	return nil, err
	}

	ec2BuildletSpan := lg.CreateSpan("create_ec2_buildlet", instName)
	defer func() { ec2BuildletSpan.Done(err) }()

	var (
	createSpan = lg.CreateSpan("create_ec2_instance", instName)
	waitBuildlet spanlog.Span
	curSpan = createSpan
	instanceCreated bool
	)
	bc, err := eb.buildletClient.StartNewVM(ctx, eb.buildEnv, hconf, instName, hostType, &buildlet.VMOpts{
	Zone: "", // allow the EC2 api pick an availability zone with capacity
	TLS: kp,
	Meta: make(map[string]string),
	DeleteIn: deleteTimeoutFromContextOrValue(ctx, eb.vmDeleteTimeout),
	OnInstanceRequested: func() {
	log.Printf("EC2 VM %q now booting", instName)
	},
	OnInstanceCreated: func() {
	log.Printf("EC2 VM %q now running", instName)
	createSpan.Done(nil)
	instanceCreated = true
	waitBuildlet = lg.CreateSpan("wait_buildlet_start", instName)
	curSpan = waitBuildlet
	},
	OnGotEC2InstanceInfo: func(inst *cloud.Instance) {
	lg.LogEventTime("got_instance_info", "waiting_for_buildlet...")
	eb.ledger.UpdateReservation(instName, inst.ID)
	},
	})
	if err != nil {
	curSpan.Done(err)
	log.Printf("EC2 VM creation failed for %s: %v", hostType, err)
	if instanceCreated {
	log.Printf("EC2 VM %q failed initialize buildlet client. deleting...", instName)
	eb.buildletDone(instName)
	} else {
	eb.ledger.Remove(instName)
	}
	return nil, err
	}
	waitBuildlet.Done(nil)
	bc.SetDescription(fmt.Sprintf("EC2 VM: %s", instName))
	bc.SetOnHeartbeatFailure(func() {
	log.Printf("EC2 VM %q failed heartbeat", instName)
	eb.buildletDone(instName)
	})
	return bc, nil
	}

	// String gives a report of capacity usage for the EC2 buildlet pool.
	func (eb *EC2Buildlet) String() string {
	return fmt.Sprintf("EC2 pool capacity: %s", eb.capacityString())
	}

	// capacityString() gives a report of capacity usage.
	func (eb *EC2Buildlet) capacityString() string {
	r := eb.ledger.Resources()
	return fmt.Sprintf("%d instances; %d/%d CPUs", r.InstCount, r.CPUUsed, r.CPULimit)
	}

	// WriteHTMLStatus writes the status of the EC2 buildlet pool to an io.Writer.
	func (eb *EC2Buildlet) WriteHTMLStatus(w io.Writer) {
	fmt.Fprintf(w, "<b>EC2 pool</b> capacity: %s", eb.capacityString())

	active := eb.ledger.ResourceTime()
	if len(active) > 0 {
	fmt.Fprintf(w, "<ul>")
	for _, inst := range active {
	fmt.Fprintf(w, "<li>%v, %s</li>\n", html.EscapeString(inst.Name), friendlyDuration(time.Since(inst.Creation)))
	}
	fmt.Fprintf(w, "</ul>")
	}
	}

	// buildletDone issues a call to destroy the EC2 instance and removes
	// the instance from the ledger. Removing the instance from the ledger
	// also releases any resources allocated to that instance. If an instance
	// is not found in the ledger or on EC2 then an error is logged. All
	// untracked instances will be cleaned up by the polling cleanupUnusedVMs
	// method.
	func (eb *EC2Buildlet) buildletDone(instName string) {
	vmID := eb.ledger.InstanceID(instName)
	if vmID == "" {
	log.Printf("EC2 vm %s not found", instName)
	return
	}
	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()
	if err := eb.awsClient.DestroyInstances(ctx, vmID); err != nil {
	log.Printf("EC2 VM %s deletion failed: %s", instName, err)
	}
	eb.ledger.Remove(instName)
	}

	// Close stops the pollers used by the EC2Buildlet pool from running.
	func (eb *EC2Buildlet) Close() {
	eb.once.Do(func() {
	close(eb.done)
	})
	}

	// retrieveAndSetQuota queries EC2 for account relevant quotas and sets the quota in the ledger.
	func (eb *EC2Buildlet) retrieveAndSetQuota() error {
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()

	cpuQuota, err := eb.awsClient.Quota(ctx, cloud.QuotaServiceEC2, cloud.QuotaCodeCPUOnDemand)
	if err != nil {
	log.Printf("unable to query for cpu quota: %s", err)
	return err
	}
	eb.ledger.SetCPULimit(cpuQuota)
	return nil
	}

	// pollQuota repeatedly polls for the EC2 quota data and sets the quota data in
	// the ledger. It stops polling once the done channel has been closed.
	func (eb *EC2Buildlet) pollQuota() {
	t := time.NewTicker(time.Hour)
	defer t.Stop()
	for {
	select {
	case <-t.C:
	err := eb.retrieveAndSetQuota()
	if err != nil {
	log.Printf("polling for EC2 quota failed: %s", err)
	}
	case <-eb.done:
	// closing the done channel signals the end of the polling loop.
	log.Printf("stopped polling for EC2 quota")
	return
	}
	}
	}

	// retrieveAndSetInstanceTypes retrieves the ARM64 instance types from the EC2
	// service and sets them in the ledger.
	func (eb *EC2Buildlet) retrieveAndSetInstanceTypes() error {
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()

	its, err := eb.awsClient.InstanceTypesARM(ctx)
	if err != nil {
	return fmt.Errorf("unable to retrieve instance types: %w", err)
	}
	eb.ledger.UpdateInstanceTypes(its)
	log.Printf("ec2 buildlet pool instance types updated")
	return nil
	}

	// cleanupUnusedVMs periodically queries for VMs which are not tracked in the ledger and
	// deletes them. If the done channel has been closed then the polling will exit.
	func (eb *EC2Buildlet) cleanupUnusedVMs() {
	t := time.NewTicker(2 * time.Minute)
	defer t.Stop()
	for {
	select {
	case <-t.C:
	log.Printf("cleaning up unused EC2 instances")
	eb.destroyUntrackedInstances()
	case <-eb.done:
	// closing the done channel signals the end of the polling loop.
	log.Printf("stopped cleaning up unused EC2 instances")
	return
	}
	}
	}

	// destroyUntrackedInstances searches for VMs which exist but are not being tracked in the
	// ledger and deletes them.
	func (eb *EC2Buildlet) destroyUntrackedInstances() {
	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
	defer cancel()

	insts, err := eb.awsClient.RunningInstances(ctx)
	if err != nil {
	log.Printf("failed to query for instances: %s", err)
	return
	}
	deleteInsts := make([]string, 0, len(insts))
	for _, inst := range insts {
	if eb.isRemoteBuildlet(inst.Name) {
	// Remote buildlets have their own expiration mechanism that respects active SSH sessions.
	log.Printf("destroyUntrackedInstances: skipping remote buildlet %q", inst.Name)
	continue
	}
	if id := eb.ledger.InstanceID(inst.Name); id != "" {
	continue
	}
	deleteInsts = append(deleteInsts, inst.ID)
	log.Printf("queued for deleting untracked EC2 VM %q with id %q", inst.Name, inst.ID)
	}
	if len(deleteInsts) == 0 {
	return
	}
	if err := eb.awsClient.DestroyInstances(ctx, deleteInsts...); err != nil {
	log.Printf("failed cleaning EC2 VMs: %s", err)
	}
	}