open-nomad/command/agent/consul/client.go

package consul

import (
	"fmt"
	"log"
	"net"
	"net/url"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	metrics "github.com/armon/go-metrics"
	"github.com/hashicorp/consul/api"
	"github.com/hashicorp/nomad/client/driver"
	cstructs "github.com/hashicorp/nomad/client/structs"
	"github.com/hashicorp/nomad/nomad/structs"
)

const (
	// nomadServicePrefix is the first prefix that scopes all Nomad registered
	// services
	nomadServicePrefix = "_nomad"

	// defaultRetryInterval is how quickly to retry syncing services and
	// checks to Consul when an error occurs. Will backoff up to a max.
	defaultRetryInterval = time.Second

	// defaultMaxRetryInterval is the default max retry interval.
	defaultMaxRetryInterval = 30 * time.Second

	// ttlCheckBuffer is the time interval that Nomad can take to report Consul
	// the check result
	ttlCheckBuffer = 31 * time.Second

	// defaultShutdownWait is how long Shutdown() should block waiting for
	// enqueued operations to sync to Consul by default.
	defaultShutdownWait = time.Minute

	// DefaultQueryWaitDuration is the max duration the Consul Agent will
	// spend waiting for a response from a Consul Query.
	DefaultQueryWaitDuration = 2 * time.Second

	// ServiceTagHTTP is the tag assigned to HTTP services
	ServiceTagHTTP = "http"

	// ServiceTagRPC is the tag assigned to RPC services
	ServiceTagRPC = "rpc"

	// ServiceTagSerf is the tag assigned to Serf services
	ServiceTagSerf = "serf"
)

// CatalogAPI is the consul/api.Catalog API used by Nomad.
type CatalogAPI interface {
	Datacenters() ([]string, error)
	Service(service, tag string, q *api.QueryOptions) ([]*api.CatalogService, *api.QueryMeta, error)
}

// AgentAPI is the consul/api.Agent API used by Nomad.
type AgentAPI interface {
	Services() (map[string]*api.AgentService, error)
	Checks() (map[string]*api.AgentCheck, error)
	CheckRegister(check *api.AgentCheckRegistration) error
	CheckDeregister(checkID string) error
	ServiceRegister(service *api.AgentServiceRegistration) error
	ServiceDeregister(serviceID string) error
	UpdateTTL(id, output, status string) error
}

// addrParser is usually the Task.FindHostAndPortFor method for turning a
// portLabel into an address and port.
type addrParser func(portLabel string) (string, int)

// operations are submitted to the main loop via commit() for synchronizing
// with Consul.
type operations struct {
	regServices []*api.AgentServiceRegistration
	regChecks   []*api.AgentCheckRegistration
	scripts     []*scriptCheck

	deregServices []string
	deregChecks   []string
}

// ServiceClient handles task and agent service registration with Consul.
type ServiceClient struct {
	client           AgentAPI
	logger           *log.Logger
	retryInterval    time.Duration
	maxRetryInterval time.Duration

	// skipVerifySupport is true if the local Consul agent suppots TLSSkipVerify
	skipVerifySupport bool

	// exitCh is closed when the main Run loop exits
	exitCh chan struct{}

	// shutdownCh is closed when the client should shutdown
	shutdownCh chan struct{}

	// shutdownWait is how long Shutdown() blocks waiting for the final
	// sync() to finish. Defaults to defaultShutdownWait
	shutdownWait time.Duration

	opCh chan *operations

	services       map[string]*api.AgentServiceRegistration
	checks         map[string]*api.AgentCheckRegistration
	scripts        map[string]*scriptCheck
	runningScripts map[string]*scriptHandle

	// agent services and checks record entries for the agent itself which
	// should be removed on shutdown
	agentServices map[string]struct{}
	agentChecks   map[string]struct{}
	agentLock     sync.Mutex

	// seen is 1 if Consul has ever been seen; otherise 0. Accessed with
	// atomics.
	seen int32
}

// NewServiceClient creates a new Consul ServiceClient from an existing Consul API
// Client and logger.
func NewServiceClient(consulClient AgentAPI, skipVerifySupport bool, logger *log.Logger) *ServiceClient {
	return &ServiceClient{
		client:            consulClient,
		skipVerifySupport: skipVerifySupport,
		logger:            logger,
		retryInterval:     defaultRetryInterval,
		maxRetryInterval:  defaultMaxRetryInterval,
		exitCh:            make(chan struct{}),
		shutdownCh:        make(chan struct{}),
		shutdownWait:      defaultShutdownWait,
		opCh:              make(chan *operations, 8),
		services:          make(map[string]*api.AgentServiceRegistration),
		checks:            make(map[string]*api.AgentCheckRegistration),
		scripts:           make(map[string]*scriptCheck),
		runningScripts:    make(map[string]*scriptHandle),
		agentServices:     make(map[string]struct{}),
		agentChecks:       make(map[string]struct{}),
	}
}

// seen is used by markSeen and hasSeen
const seen = 1

// markSeen marks Consul as having been seen (meaning at least one operation
// has succeeded).
func (c *ServiceClient) markSeen() {
	atomic.StoreInt32(&c.seen, seen)
}

// hasSeen returns true if any Consul operation has ever succeeded. Useful to
// squelch errors if Consul isn't running.
func (c *ServiceClient) hasSeen() bool {
	return atomic.LoadInt32(&c.seen) == seen
}

// Run the Consul main loop which retries operations against Consul. It should
// be called exactly once.
func (c *ServiceClient) Run() {
	defer close(c.exitCh)
	retryTimer := time.NewTimer(0)
	<-retryTimer.C // disabled by default
	failures := 0
	for {
		select {
		case <-retryTimer.C:
		case <-c.shutdownCh:
		case ops := <-c.opCh:
			c.merge(ops)
		}

		if err := c.sync(); err != nil {
			if failures == 0 {
				c.logger.Printf("[WARN] consul.sync: failed to update services in Consul: %v", err)
			}
			failures++
			if !retryTimer.Stop() {
				// Timer already expired, since the timer may
				// or may not have been read in the select{}
				// above, conditionally receive on it
				select {
				case <-retryTimer.C:
				default:
				}
			}
			backoff := c.retryInterval * time.Duration(failures)
			if backoff > c.maxRetryInterval {
				backoff = c.maxRetryInterval
			}
			retryTimer.Reset(backoff)
		} else {
			if failures > 0 {
				c.logger.Printf("[INFO] consul.sync: successfully updated services in Consul")
				failures = 0
			}
		}

		select {
		case <-c.shutdownCh:
			// Exit only after sync'ing all outstanding operations
			if len(c.opCh) > 0 {
				for len(c.opCh) > 0 {
					c.merge(<-c.opCh)
				}
				continue
			}
			return
		default:
		}

	}
}

// commit operations unless already shutting down.
func (c *ServiceClient) commit(ops *operations) {
	select {
	case c.opCh <- ops:
	case <-c.shutdownCh:
	}
}

// merge registrations into state map prior to sync'ing with Consul
func (c *ServiceClient) merge(ops *operations) {
	for _, s := range ops.regServices {
		c.services[s.ID] = s
	}
	for _, check := range ops.regChecks {
		c.checks[check.ID] = check
	}
	for _, s := range ops.scripts {
		c.scripts[s.id] = s
	}
	for _, sid := range ops.deregServices {
		delete(c.services, sid)
	}
	for _, cid := range ops.deregChecks {
		if script, ok := c.runningScripts[cid]; ok {
			script.cancel()
			delete(c.scripts, cid)
			delete(c.runningScripts, cid)
		}
		delete(c.checks, cid)
	}
	metrics.SetGauge([]string{"client", "consul", "services"}, float32(len(c.services)))
	metrics.SetGauge([]string{"client", "consul", "checks"}, float32(len(c.checks)))
	metrics.SetGauge([]string{"client", "consul", "script_checks"}, float32(len(c.runningScripts)))
}

// sync enqueued operations.
func (c *ServiceClient) sync() error {
	sreg, creg, sdereg, cdereg := 0, 0, 0, 0

	consulServices, err := c.client.Services()
	if err != nil {
		metrics.IncrCounter([]string{"client", "consul", "sync_failure"}, 1)
		return fmt.Errorf("error querying Consul services: %v", err)
	}

	consulChecks, err := c.client.Checks()
	if err != nil {
		metrics.IncrCounter([]string{"client", "consul", "sync_failure"}, 1)
		return fmt.Errorf("error querying Consul checks: %v", err)
	}

	// Remove Nomad services in Consul but unknown locally
	for id := range consulServices {
		if _, ok := c.services[id]; ok {
			// Known service, skip
			continue
		}
		if !isNomadService(id) {
			// Not managed by Nomad, skip
			continue
		}
		// Unknown Nomad managed service; kill
		if err := c.client.ServiceDeregister(id); err != nil {
			metrics.IncrCounter([]string{"client", "consul", "sync_failure"}, 1)
			return err
		}
		sdereg++
		metrics.IncrCounter([]string{"client", "consul", "service_deregisrations"}, 1)
	}

	// Track services whose ports have changed as their checks may also
	// need updating
	portsChanged := make(map[string]struct{}, len(c.services))

	// Add Nomad services missing from Consul
	for id, locals := range c.services {
		if remotes, ok := consulServices[id]; ok {
			// Make sure Port and Address are stable since
			// PortLabel and AddressMode aren't included in the
			// service ID.
			if locals.Port == remotes.Port && locals.Address == remotes.Address {
				// Already exists in Consul; skip
				continue
			}
			// Port changed, reregister it and its checks
			portsChanged[id] = struct{}{}
		}
		if err = c.client.ServiceRegister(locals); err != nil {
			metrics.IncrCounter([]string{"client", "consul", "sync_failure"}, 1)
			return err
		}
		sreg++
		metrics.IncrCounter([]string{"client", "consul", "service_regisrations"}, 1)
	}

	// Remove Nomad checks in Consul but unknown locally
	for id, check := range consulChecks {
		if _, ok := c.checks[id]; ok {
			// Known check, leave it
			continue
		}
		if !isNomadService(check.ServiceID) {
			// Service not managed by Nomad, skip
			continue
		}
		// Unknown Nomad managed check; kill
		if err := c.client.CheckDeregister(id); err != nil {
			metrics.IncrCounter([]string{"client", "consul", "sync_failure"}, 1)
			return err
		}
		cdereg++
		metrics.IncrCounter([]string{"client", "consul", "check_deregisrations"}, 1)
	}

	// Add Nomad checks missing from Consul
	for id, check := range c.checks {
		if check, ok := consulChecks[id]; ok {
			if _, changed := portsChanged[check.ServiceID]; !changed {
				// Already in Consul and ports didn't change; skipping
				continue
			}
		}
		if err := c.client.CheckRegister(check); err != nil {
			metrics.IncrCounter([]string{"client", "consul", "sync_failure"}, 1)
			return err
		}
		creg++
		metrics.IncrCounter([]string{"client", "consul", "check_regisrations"}, 1)

		// Handle starting scripts
		if script, ok := c.scripts[id]; ok {
			// If it's already running, cancel and replace
			if oldScript, running := c.runningScripts[id]; running {
				oldScript.cancel()
			}
			// Start and store the handle
			c.runningScripts[id] = script.run()
		}
	}

	// A Consul operation has succeeded, mark Consul as having been seen
	c.markSeen()

	c.logger.Printf("[DEBUG] consul.sync: registered %d services, %d checks; deregistered %d services, %d checks",
		sreg, creg, sdereg, cdereg)
	return nil
}

// RegisterAgent registers Nomad agents (client or server). The
// Service.PortLabel should be a literal port to be parsed with SplitHostPort.
// Script checks are not supported and will return an error. Registration is
// asynchronous.
//
// Agents will be deregistered when Shutdown is called.
func (c *ServiceClient) RegisterAgent(role string, services []*structs.Service) error {
	ops := operations{}

	for _, service := range services {
		id := makeAgentServiceID(role, service)

		// Unlike tasks, agents don't use port labels. Agent ports are
		// stored directly in the PortLabel.
		host, rawport, err := net.SplitHostPort(service.PortLabel)
		if err != nil {
			return fmt.Errorf("error parsing port label %q from service %q: %v", service.PortLabel, service.Name, err)
		}
		port, err := strconv.Atoi(rawport)
		if err != nil {
			return fmt.Errorf("error parsing port %q from service %q: %v", rawport, service.Name, err)
		}
		serviceReg := &api.AgentServiceRegistration{
			ID:      id,
			Name:    service.Name,
			Tags:    service.Tags,
			Address: host,
			Port:    port,
		}
		ops.regServices = append(ops.regServices, serviceReg)

		for _, check := range service.Checks {
			checkID := makeCheckID(id, check)
			if check.Type == structs.ServiceCheckScript {
				return fmt.Errorf("service %q contains invalid check: agent checks do not support scripts", service.Name)
			}
			checkHost, checkPort := serviceReg.Address, serviceReg.Port
			if check.PortLabel != "" {
				// Unlike tasks, agents don't use port labels. Agent ports are
				// stored directly in the PortLabel.
				host, rawport, err := net.SplitHostPort(check.PortLabel)
				if err != nil {
					return fmt.Errorf("error parsing port label %q from check %q: %v", service.PortLabel, check.Name, err)
				}
				port, err := strconv.Atoi(rawport)
				if err != nil {
					return fmt.Errorf("error parsing port %q from check %q: %v", rawport, check.Name, err)
				}
				checkHost, checkPort = host, port
			}
			checkReg, err := createCheckReg(id, checkID, check, checkHost, checkPort)
			if err != nil {
				return fmt.Errorf("failed to add check %q: %v", check.Name, err)
			}
			ops.regChecks = append(ops.regChecks, checkReg)
		}
	}

	// Don't bother committing agent checks if we're already shutting down
	c.agentLock.Lock()
	defer c.agentLock.Unlock()
	select {
	case <-c.shutdownCh:
		return nil
	default:
	}

	// Now add them to the registration queue
	c.commit(&ops)

	// Record IDs for deregistering on shutdown
	for _, id := range ops.regServices {
		c.agentServices[id.ID] = struct{}{}
	}
	for _, id := range ops.regChecks {
		c.agentChecks[id.ID] = struct{}{}
	}
	return nil
}

// serviceRegs creates service registrations, check registrations, and script
// checks from a service.
func (c *ServiceClient) serviceRegs(ops *operations, allocID string, service *structs.Service,
	task *structs.Task, exec driver.ScriptExecutor, net *cstructs.DriverNetwork) error {

	id := makeTaskServiceID(allocID, task.Name, service)
	addrMode := service.AddressMode
	if addrMode == structs.AddressModeAuto {
		if net.Advertise() {
			addrMode = structs.AddressModeDriver
		} else {
			// No driver network or shouldn't default to driver's network
			addrMode = structs.AddressModeHost
		}
	}
	ip, port := task.Resources.Networks.Port(service.PortLabel)
	if addrMode == structs.AddressModeDriver {
		if net == nil {
			return fmt.Errorf("service %s cannot use driver's IP because driver didn't set one", service.Name)
		}
		ip = net.IP
		port = net.PortMap[service.PortLabel]
	}
	serviceReg := &api.AgentServiceRegistration{
		ID:      id,
		Name:    service.Name,
		Tags:    make([]string, len(service.Tags)),
		Address: ip,
		Port:    port,
	}
	// copy isn't strictly necessary but can avoid bugs especially
	// with tests that may reuse Tasks
	copy(serviceReg.Tags, service.Tags)
	ops.regServices = append(ops.regServices, serviceReg)
	return c.checkRegs(ops, allocID, id, service, task, exec, net)
}

func (c *ServiceClient) checkRegs(ops *operations, allocID, serviceID string, service *structs.Service,
	task *structs.Task, exec driver.ScriptExecutor, net *cstructs.DriverNetwork) error {

	for _, check := range service.Checks {
		if check.TLSSkipVerify && !c.skipVerifySupport {
			c.logger.Printf("[WARN] consul.sync: skipping check %q for task %q alloc %q because Consul doesn't support tls_skip_verify. Please upgrade to Consul >= 0.7.2.",
				check.Name, task.Name, allocID)
			continue
		}
		checkID := makeCheckID(serviceID, check)
		if check.Type == structs.ServiceCheckScript {
			if exec == nil {
				return fmt.Errorf("driver doesn't support script checks")
			}
			ops.scripts = append(ops.scripts, newScriptCheck(
				allocID, task.Name, checkID, check, exec, c.client, c.logger, c.shutdownCh))

		}

		// Checks should always use the host ip:port
		portLabel := check.PortLabel
		if portLabel == "" {
			// Default to the service's port label
			portLabel = service.PortLabel
		}
		ip, port := task.Resources.Networks.Port(portLabel)
		checkReg, err := createCheckReg(serviceID, checkID, check, ip, port)
		if err != nil {
			return fmt.Errorf("failed to add check %q: %v", check.Name, err)
		}
		ops.regChecks = append(ops.regChecks, checkReg)
	}
	return nil
}

// RegisterTask with Consul. Adds all service entries and checks to Consul. If
// exec is nil and a script check exists an error is returned.
//
// If the service IP is set it used as the address in the service registration.
// Checks will always use the IP from the Task struct (host's IP).
//
// Actual communication with Consul is done asynchrously (see Run).
func (c *ServiceClient) RegisterTask(allocID string, task *structs.Task, exec driver.ScriptExecutor, net *cstructs.DriverNetwork) error {
	ops := &operations{}
	for _, service := range task.Services {
		if err := c.serviceRegs(ops, allocID, service, task, exec, net); err != nil {
			return err
		}
	}
	c.commit(ops)
	return nil
}

// UpdateTask in Consul. Does not alter the service if only checks have
// changed.
//
// DriverNetwork must not change between invocations for the same allocation.
func (c *ServiceClient) UpdateTask(allocID string, existing, newTask *structs.Task, exec driver.ScriptExecutor, net *cstructs.DriverNetwork) error {
	ops := &operations{}

	existingIDs := make(map[string]*structs.Service, len(existing.Services))
	for _, s := range existing.Services {
		existingIDs[makeTaskServiceID(allocID, existing.Name, s)] = s
	}
	newIDs := make(map[string]*structs.Service, len(newTask.Services))
	for _, s := range newTask.Services {
		newIDs[makeTaskServiceID(allocID, newTask.Name, s)] = s
	}

	// Loop over existing Service IDs to see if they have been removed or
	// updated.
	for existingID, existingSvc := range existingIDs {
		newSvc, ok := newIDs[existingID]
		if !ok {
			// Existing service entry removed
			ops.deregServices = append(ops.deregServices, existingID)
			for _, check := range existingSvc.Checks {
				ops.deregChecks = append(ops.deregChecks, makeCheckID(existingID, check))
			}
			continue
		}

		// PortLabel and AddressMode aren't included in the ID, so we
		// have to compare manually.
		serviceUnchanged := newSvc.PortLabel == existingSvc.PortLabel && newSvc.AddressMode == existingSvc.AddressMode
		if serviceUnchanged {
			// Service exists and hasn't changed, don't add it later
			delete(newIDs, existingID)
		}

		// Check to see what checks were updated
		existingChecks := make(map[string]struct{}, len(existingSvc.Checks))
		for _, check := range existingSvc.Checks {
			existingChecks[makeCheckID(existingID, check)] = struct{}{}
		}

		// Register new checks
		for _, check := range newSvc.Checks {
			checkID := makeCheckID(existingID, check)
			if _, exists := existingChecks[checkID]; exists {
				// Check exists, so don't remove it
				delete(existingChecks, checkID)
			} else if serviceUnchanged {
				// New check on an unchanged service; add them now
				err := c.checkRegs(ops, allocID, existingID, newSvc, newTask, exec, net)
				if err != nil {
					return err
				}
			}
		}

		// Remove existing checks not in updated service
		for cid := range existingChecks {
			ops.deregChecks = append(ops.deregChecks, cid)
		}
	}

	// Any remaining services should just be enqueued directly
	for _, newSvc := range newIDs {
		err := c.serviceRegs(ops, allocID, newSvc, newTask, exec, net)
		if err != nil {
			return err
		}
	}

	c.commit(ops)
	return nil
}

// RemoveTask from Consul. Removes all service entries and checks.
//
// Actual communication with Consul is done asynchrously (see Run).
func (c *ServiceClient) RemoveTask(allocID string, task *structs.Task) {
	ops := operations{}

	for _, service := range task.Services {
		id := makeTaskServiceID(allocID, task.Name, service)
		ops.deregServices = append(ops.deregServices, id)

		for _, check := range service.Checks {
			ops.deregChecks = append(ops.deregChecks, makeCheckID(id, check))
		}
	}

	// Now add them to the deregistration fields; main Run loop will update
	c.commit(&ops)
}

// Checks returns the checks registered against the agent for the given
// allocation.
func (c *ServiceClient) Checks(a *structs.Allocation) ([]*api.AgentCheck, error) {
	tg := a.Job.LookupTaskGroup(a.TaskGroup)
	if tg == nil {
		return nil, fmt.Errorf("failed to find task group in alloc")
	}

	// Determine the checks that are relevant
	relevant := make(map[string]struct{}, 4)
	for _, task := range tg.Tasks {
		for _, service := range task.Services {
			id := makeTaskServiceID(a.ID, task.Name, service)
			for _, check := range service.Checks {
				relevant[makeCheckID(id, check)] = struct{}{}
			}
		}
	}

	// Query all the checks
	checks, err := c.client.Checks()
	if err != nil {
		return nil, err
	}

	allocChecks := make([]*api.AgentCheck, 0, len(relevant))
	for checkID := range relevant {
		if check, ok := checks[checkID]; ok {
			allocChecks = append(allocChecks, check)
		}
	}

	return allocChecks, nil
}

// Shutdown the Consul client. Update running task registations and deregister
// agent from Consul. On first call blocks up to shutdownWait before giving up
// on syncing operations.
func (c *ServiceClient) Shutdown() error {
	// Serialize Shutdown calls with RegisterAgent to prevent leaking agent
	// entries.
	c.agentLock.Lock()
	defer c.agentLock.Unlock()
	select {
	case <-c.shutdownCh:
		return nil
	default:
		close(c.shutdownCh)
	}

	// Give run loop time to sync, but don't block indefinitely
	deadline := time.After(c.shutdownWait)

	// Wait for Run to finish any outstanding operations and exit
	select {
	case <-c.exitCh:
	case <-deadline:
		// Don't wait forever though
	}

	// If Consul was never seen nothing could be written so exit early
	if !c.hasSeen() {
		return nil
	}

	// Always attempt to deregister Nomad agent Consul entries, even if
	// deadline was reached
	for id := range c.agentServices {
		if err := c.client.ServiceDeregister(id); err != nil {
			c.logger.Printf("[ERR] consul.sync: error deregistering agent service (id: %q): %v", id, err)
		}
	}
	for id := range c.agentChecks {
		if err := c.client.CheckDeregister(id); err != nil {
			c.logger.Printf("[ERR] consul.sync: error deregistering agent service (id: %q): %v", id, err)
		}
	}

	// Give script checks time to exit (no need to lock as Run() has exited)
	for _, h := range c.runningScripts {
		select {
		case <-h.wait():
		case <-deadline:
			return fmt.Errorf("timed out waiting for script checks to run")
		}
	}
	return nil
}

// makeAgentServiceID creates a unique ID for identifying an agent service in
// Consul.
//
// Agent service IDs are of the form:
//
//	{nomadServicePrefix}-{ROLE}-{Service.Name}-{Service.Tags...}
//	Example Server ID: _nomad-server-nomad-serf
//	Example Client ID: _nomad-client-nomad-client-http
//
func makeAgentServiceID(role string, service *structs.Service) string {
	parts := make([]string, len(service.Tags)+3)
	parts[0] = nomadServicePrefix
	parts[1] = role
	parts[2] = service.Name
	copy(parts[3:], service.Tags)
	return strings.Join(parts, "-")
}

// makeTaskServiceID creates a unique ID for identifying a task service in
// Consul.
//
// Task service IDs are of the form:
//
//	{nomadServicePrefix}-executor-{ALLOC_ID}-{Service.Name}-{Service.Tags...}
//	Example Service ID: _nomad-executor-1234-echo-http-tag1-tag2-tag3
//
func makeTaskServiceID(allocID, taskName string, service *structs.Service) string {
	parts := make([]string, len(service.Tags)+5)
	parts[0] = nomadServicePrefix
	parts[1] = "executor"
	parts[2] = allocID
	parts[3] = taskName
	parts[4] = service.Name
	copy(parts[5:], service.Tags)
	return strings.Join(parts, "-")
}

// makeCheckID creates a unique ID for a check.
func makeCheckID(serviceID string, check *structs.ServiceCheck) string {
	return check.Hash(serviceID)
}

// createCheckReg creates a Check that can be registered with Consul.
//
// Script checks simply have a TTL set and the caller is responsible for
// running the script and heartbeating.
func createCheckReg(serviceID, checkID string, check *structs.ServiceCheck, host string, port int) (*api.AgentCheckRegistration, error) {
	chkReg := api.AgentCheckRegistration{
		ID:        checkID,
		Name:      check.Name,
		ServiceID: serviceID,
	}
	chkReg.Status = check.InitialStatus
	chkReg.Timeout = check.Timeout.String()
	chkReg.Interval = check.Interval.String()

	switch check.Type {
	case structs.ServiceCheckHTTP:
		proto := check.Protocol
		if proto == "" {
			proto = "http"
		}
		if check.TLSSkipVerify {
			chkReg.TLSSkipVerify = true
		}
		base := url.URL{
			Scheme: proto,
			Host:   net.JoinHostPort(host, strconv.Itoa(port)),
		}
		relative, err := url.Parse(check.Path)
		if err != nil {
			return nil, err
		}
		url := base.ResolveReference(relative)
		chkReg.HTTP = url.String()
	case structs.ServiceCheckTCP:
		chkReg.TCP = net.JoinHostPort(host, strconv.Itoa(port))
	case structs.ServiceCheckScript:
		chkReg.TTL = (check.Interval + ttlCheckBuffer).String()
	default:
		return nil, fmt.Errorf("check type %+q not valid", check.Type)
	}
	return &chkReg, nil
}

// isNomadService returns true if the ID matches the pattern of a Nomad managed
// service. Agent services return false as independent client and server agents
// may be running on the same machine. #2827
func isNomadService(id string) bool {
	const prefix = nomadServicePrefix + "-executor"
	return strings.HasPrefix(id, prefix)
}