swarm: integrate OpenTracing; propagate ctx to internal APIs (#17169)

* swarm: propagate ctx, enable opentracing

* swarm/tracing: log error when tracing is misconfigured

vendor/github.com/uber/jaeger-client-go/config/config.go

@@ -0,0 +1,373 @@
+// Copyright (c) 2017-2018 Uber Technologies, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package config
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"strings"
+	"time"
+
+	"github.com/opentracing/opentracing-go"
+
+	"github.com/uber/jaeger-client-go"
+	"github.com/uber/jaeger-client-go/internal/baggage/remote"
+	throttler "github.com/uber/jaeger-client-go/internal/throttler/remote"
+	"github.com/uber/jaeger-client-go/rpcmetrics"
+)
+
+const defaultSamplingProbability = 0.001
+
+// Configuration configures and creates Jaeger Tracer
+type Configuration struct {
+	// ServiceName specifies the service name to use on the tracer.
+	// Can be provided via environment variable named JAEGER_SERVICE_NAME
+	ServiceName string `yaml:"serviceName"`
+
+	// Disabled can be provided via environment variable named JAEGER_DISABLED
+	Disabled bool `yaml:"disabled"`
+
+	// RPCMetrics can be provided via environment variable named JAEGER_RPC_METRICS
+	RPCMetrics bool `yaml:"rpc_metrics"`
+
+	// Tags can be provided via environment variable named JAEGER_TAGS
+	Tags []opentracing.Tag `yaml:"tags"`
+
+	Sampler             *SamplerConfig             `yaml:"sampler"`
+	Reporter            *ReporterConfig            `yaml:"reporter"`
+	Headers             *jaeger.HeadersConfig      `yaml:"headers"`
+	BaggageRestrictions *BaggageRestrictionsConfig `yaml:"baggage_restrictions"`
+	Throttler           *ThrottlerConfig           `yaml:"throttler"`
+}
+
+// SamplerConfig allows initializing a non-default sampler.  All fields are optional.
+type SamplerConfig struct {
+	// Type specifies the type of the sampler: const, probabilistic, rateLimiting, or remote
+	// Can be set by exporting an environment variable named JAEGER_SAMPLER_TYPE
+	Type string `yaml:"type"`
+
+	// Param is a value passed to the sampler.
+	// Valid values for Param field are:
+	// - for "const" sampler, 0 or 1 for always false/true respectively
+	// - for "probabilistic" sampler, a probability between 0 and 1
+	// - for "rateLimiting" sampler, the number of spans per second
+	// - for "remote" sampler, param is the same as for "probabilistic"
+	//   and indicates the initial sampling rate before the actual one
+	//   is received from the mothership.
+	// Can be set by exporting an environment variable named JAEGER_SAMPLER_PARAM
+	Param float64 `yaml:"param"`
+
+	// SamplingServerURL is the address of jaeger-agent's HTTP sampling server
+	// Can be set by exporting an environment variable named JAEGER_SAMPLER_MANAGER_HOST_PORT
+	SamplingServerURL string `yaml:"samplingServerURL"`
+
+	// MaxOperations is the maximum number of operations that the sampler
+	// will keep track of. If an operation is not tracked, a default probabilistic
+	// sampler will be used rather than the per operation specific sampler.
+	// Can be set by exporting an environment variable named JAEGER_SAMPLER_MAX_OPERATIONS
+	MaxOperations int `yaml:"maxOperations"`
+
+	// SamplingRefreshInterval controls how often the remotely controlled sampler will poll
+	// jaeger-agent for the appropriate sampling strategy.
+	// Can be set by exporting an environment variable named JAEGER_SAMPLER_REFRESH_INTERVAL
+	SamplingRefreshInterval time.Duration `yaml:"samplingRefreshInterval"`
+}
+
+// ReporterConfig configures the reporter. All fields are optional.
+type ReporterConfig struct {
+	// QueueSize controls how many spans the reporter can keep in memory before it starts dropping
+	// new spans. The queue is continuously drained by a background go-routine, as fast as spans
+	// can be sent out of process.
+	// Can be set by exporting an environment variable named JAEGER_REPORTER_MAX_QUEUE_SIZE
+	QueueSize int `yaml:"queueSize"`
+
+	// BufferFlushInterval controls how often the buffer is force-flushed, even if it's not full.
+	// It is generally not useful, as it only matters for very low traffic services.
+	// Can be set by exporting an environment variable named JAEGER_REPORTER_FLUSH_INTERVAL
+	BufferFlushInterval time.Duration
+
+	// LogSpans, when true, enables LoggingReporter that runs in parallel with the main reporter
+	// and logs all submitted spans. Main Configuration.Logger must be initialized in the code
+	// for this option to have any effect.
+	// Can be set by exporting an environment variable named JAEGER_REPORTER_LOG_SPANS
+	LogSpans bool `yaml:"logSpans"`
+
+	// LocalAgentHostPort instructs reporter to send spans to jaeger-agent at this address
+	// Can be set by exporting an environment variable named JAEGER_AGENT_HOST / JAEGER_AGENT_PORT
+	LocalAgentHostPort string `yaml:"localAgentHostPort"`
+}
+
+// BaggageRestrictionsConfig configures the baggage restrictions manager which can be used to whitelist
+// certain baggage keys. All fields are optional.
+type BaggageRestrictionsConfig struct {
+	// DenyBaggageOnInitializationFailure controls the startup failure mode of the baggage restriction
+	// manager. If true, the manager will not allow any baggage to be written until baggage restrictions have
+	// been retrieved from jaeger-agent. If false, the manager wil allow any baggage to be written until baggage
+	// restrictions have been retrieved from jaeger-agent.
+	DenyBaggageOnInitializationFailure bool `yaml:"denyBaggageOnInitializationFailure"`
+
+	// HostPort is the hostPort of jaeger-agent's baggage restrictions server
+	HostPort string `yaml:"hostPort"`
+
+	// RefreshInterval controls how often the baggage restriction manager will poll
+	// jaeger-agent for the most recent baggage restrictions.
+	RefreshInterval time.Duration `yaml:"refreshInterval"`
+}
+
+// ThrottlerConfig configures the throttler which can be used to throttle the
+// rate at which the client may send debug requests.
+type ThrottlerConfig struct {
+	// HostPort of jaeger-agent's credit server.
+	HostPort string `yaml:"hostPort"`
+
+	// RefreshInterval controls how often the throttler will poll jaeger-agent
+	// for more throttling credits.
+	RefreshInterval time.Duration `yaml:"refreshInterval"`
+
+	// SynchronousInitialization determines whether or not the throttler should
+	// synchronously fetch credits from the agent when an operation is seen for
+	// the first time. This should be set to true if the client will be used by
+	// a short lived service that needs to ensure that credits are fetched
+	// upfront such that sampling or throttling occurs.
+	SynchronousInitialization bool `yaml:"synchronousInitialization"`
+}
+
+type nullCloser struct{}
+
+func (*nullCloser) Close() error { return nil }
+
+// New creates a new Jaeger Tracer, and a closer func that can be used to flush buffers
+// before shutdown.
+//
+// Deprecated: use NewTracer() function
+func (c Configuration) New(
+	serviceName string,
+	options ...Option,
+) (opentracing.Tracer, io.Closer, error) {
+	if serviceName != "" {
+		c.ServiceName = serviceName
+	}
+
+	return c.NewTracer(options...)
+}
+
+// NewTracer returns a new tracer based on the current configuration, using the given options,
+// and a closer func that can be used to flush buffers before shutdown.
+func (c Configuration) NewTracer(options ...Option) (opentracing.Tracer, io.Closer, error) {
+	if c.ServiceName == "" {
+		return nil, nil, errors.New("no service name provided")
+	}
+
+	if c.Disabled {
+		return &opentracing.NoopTracer{}, &nullCloser{}, nil
+	}
+	opts := applyOptions(options...)
+	tracerMetrics := jaeger.NewMetrics(opts.metrics, nil)
+	if c.RPCMetrics {
+		Observer(
+			rpcmetrics.NewObserver(
+				opts.metrics.Namespace("jaeger-rpc", map[string]string{"component": "jaeger"}),
+				rpcmetrics.DefaultNameNormalizer,
+			),
+		)(&opts) // adds to c.observers
+	}
+	if c.Sampler == nil {
+		c.Sampler = &SamplerConfig{
+			Type:  jaeger.SamplerTypeRemote,
+			Param: defaultSamplingProbability,
+		}
+	}
+	if c.Reporter == nil {
+		c.Reporter = &ReporterConfig{}
+	}
+
+	sampler := opts.sampler
+	if sampler == nil {
+		s, err := c.Sampler.NewSampler(c.ServiceName, tracerMetrics)
+		if err != nil {
+			return nil, nil, err
+		}
+		sampler = s
+	}
+
+	reporter := opts.reporter
+	if reporter == nil {
+		r, err := c.Reporter.NewReporter(c.ServiceName, tracerMetrics, opts.logger)
+		if err != nil {
+			return nil, nil, err
+		}
+		reporter = r
+	}
+
+	tracerOptions := []jaeger.TracerOption{
+		jaeger.TracerOptions.Metrics(tracerMetrics),
+		jaeger.TracerOptions.Logger(opts.logger),
+		jaeger.TracerOptions.CustomHeaderKeys(c.Headers),
+		jaeger.TracerOptions.Gen128Bit(opts.gen128Bit),
+		jaeger.TracerOptions.ZipkinSharedRPCSpan(opts.zipkinSharedRPCSpan),
+		jaeger.TracerOptions.MaxTagValueLength(opts.maxTagValueLength),
+	}
+
+	for _, tag := range opts.tags {
+		tracerOptions = append(tracerOptions, jaeger.TracerOptions.Tag(tag.Key, tag.Value))
+	}
+
+	for _, tag := range c.Tags {
+		tracerOptions = append(tracerOptions, jaeger.TracerOptions.Tag(tag.Key, tag.Value))
+	}
+
+	for _, obs := range opts.observers {
+		tracerOptions = append(tracerOptions, jaeger.TracerOptions.Observer(obs))
+	}
+
+	for _, cobs := range opts.contribObservers {
+		tracerOptions = append(tracerOptions, jaeger.TracerOptions.ContribObserver(cobs))
+	}
+
+	for format, injector := range opts.injectors {
+		tracerOptions = append(tracerOptions, jaeger.TracerOptions.Injector(format, injector))
+	}
+
+	for format, extractor := range opts.extractors {
+		tracerOptions = append(tracerOptions, jaeger.TracerOptions.Extractor(format, extractor))
+	}
+
+	if c.BaggageRestrictions != nil {
+		mgr := remote.NewRestrictionManager(
+			c.ServiceName,
+			remote.Options.Metrics(tracerMetrics),
+			remote.Options.Logger(opts.logger),
+			remote.Options.HostPort(c.BaggageRestrictions.HostPort),
+			remote.Options.RefreshInterval(c.BaggageRestrictions.RefreshInterval),
+			remote.Options.DenyBaggageOnInitializationFailure(
+				c.BaggageRestrictions.DenyBaggageOnInitializationFailure,
+			),
+		)
+		tracerOptions = append(tracerOptions, jaeger.TracerOptions.BaggageRestrictionManager(mgr))
+	}
+
+	if c.Throttler != nil {
+		debugThrottler := throttler.NewThrottler(
+			c.ServiceName,
+			throttler.Options.Metrics(tracerMetrics),
+			throttler.Options.Logger(opts.logger),
+			throttler.Options.HostPort(c.Throttler.HostPort),
+			throttler.Options.RefreshInterval(c.Throttler.RefreshInterval),
+			throttler.Options.SynchronousInitialization(
+				c.Throttler.SynchronousInitialization,
+			),
+		)
+
+		tracerOptions = append(tracerOptions, jaeger.TracerOptions.DebugThrottler(debugThrottler))
+	}
+
+	tracer, closer := jaeger.NewTracer(
+		c.ServiceName,
+		sampler,
+		reporter,
+		tracerOptions...,
+	)
+
+	return tracer, closer, nil
+}
+
+// InitGlobalTracer creates a new Jaeger Tracer, and sets it as global OpenTracing Tracer.
+// It returns a closer func that can be used to flush buffers before shutdown.
+func (c Configuration) InitGlobalTracer(
+	serviceName string,
+	options ...Option,
+) (io.Closer, error) {
+	if c.Disabled {
+		return &nullCloser{}, nil
+	}
+	tracer, closer, err := c.New(serviceName, options...)
+	if err != nil {
+		return nil, err
+	}
+	opentracing.SetGlobalTracer(tracer)
+	return closer, nil
+}
+
+// NewSampler creates a new sampler based on the configuration
+func (sc *SamplerConfig) NewSampler(
+	serviceName string,
+	metrics *jaeger.Metrics,
+) (jaeger.Sampler, error) {
+	samplerType := strings.ToLower(sc.Type)
+	if samplerType == jaeger.SamplerTypeConst {
+		return jaeger.NewConstSampler(sc.Param != 0), nil
+	}
+	if samplerType == jaeger.SamplerTypeProbabilistic {
+		if sc.Param >= 0 && sc.Param <= 1.0 {
+			return jaeger.NewProbabilisticSampler(sc.Param)
+		}
+		return nil, fmt.Errorf(
+			"Invalid Param for probabilistic sampler: %v. Expecting value between 0 and 1",
+			sc.Param,
+		)
+	}
+	if samplerType == jaeger.SamplerTypeRateLimiting {
+		return jaeger.NewRateLimitingSampler(sc.Param), nil
+	}
+	if samplerType == jaeger.SamplerTypeRemote || sc.Type == "" {
+		sc2 := *sc
+		sc2.Type = jaeger.SamplerTypeProbabilistic
+		initSampler, err := sc2.NewSampler(serviceName, nil)
+		if err != nil {
+			return nil, err
+		}
+		options := []jaeger.SamplerOption{
+			jaeger.SamplerOptions.Metrics(metrics),
+			jaeger.SamplerOptions.InitialSampler(initSampler),
+			jaeger.SamplerOptions.SamplingServerURL(sc.SamplingServerURL),
+		}
+		if sc.MaxOperations != 0 {
+			options = append(options, jaeger.SamplerOptions.MaxOperations(sc.MaxOperations))
+		}
+		if sc.SamplingRefreshInterval != 0 {
+			options = append(options, jaeger.SamplerOptions.SamplingRefreshInterval(sc.SamplingRefreshInterval))
+		}
+		return jaeger.NewRemotelyControlledSampler(serviceName, options...), nil
+	}
+	return nil, fmt.Errorf("Unknown sampler type %v", sc.Type)
+}
+
+// NewReporter instantiates a new reporter that submits spans to tcollector
+func (rc *ReporterConfig) NewReporter(
+	serviceName string,
+	metrics *jaeger.Metrics,
+	logger jaeger.Logger,
+) (jaeger.Reporter, error) {
+	sender, err := rc.newTransport()
+	if err != nil {
+		return nil, err
+	}
+	reporter := jaeger.NewRemoteReporter(
+		sender,
+		jaeger.ReporterOptions.QueueSize(rc.QueueSize),
+		jaeger.ReporterOptions.BufferFlushInterval(rc.BufferFlushInterval),
+		jaeger.ReporterOptions.Logger(logger),
+		jaeger.ReporterOptions.Metrics(metrics))
+	if rc.LogSpans && logger != nil {
+		logger.Infof("Initializing logging reporter\n")
+		reporter = jaeger.NewCompositeReporter(jaeger.NewLoggingReporter(logger), reporter)
+	}
+	return reporter, err
+}
+
+func (rc *ReporterConfig) newTransport() (jaeger.Transport, error) {
+	return jaeger.NewUDPTransport(rc.LocalAgentHostPort, 0)
+}

vendor/github.com/uber/jaeger-client-go/config/config_env.go

@@ -0,0 +1,205 @@
+// Copyright (c) 2018 The Jaeger Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package config
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+	"time"
+
+	opentracing "github.com/opentracing/opentracing-go"
+	"github.com/pkg/errors"
+
+	"github.com/uber/jaeger-client-go"
+)
+
+const (
+	// environment variable names
+	envServiceName            = "JAEGER_SERVICE_NAME"
+	envDisabled               = "JAEGER_DISABLED"
+	envRPCMetrics             = "JAEGER_RPC_METRICS"
+	envTags                   = "JAEGER_TAGS"
+	envSamplerType            = "JAEGER_SAMPLER_TYPE"
+	envSamplerParam           = "JAEGER_SAMPLER_PARAM"
+	envSamplerManagerHostPort = "JAEGER_SAMPLER_MANAGER_HOST_PORT"
+	envSamplerMaxOperations   = "JAEGER_SAMPLER_MAX_OPERATIONS"
+	envSamplerRefreshInterval = "JAEGER_SAMPLER_REFRESH_INTERVAL"
+	envReporterMaxQueueSize   = "JAEGER_REPORTER_MAX_QUEUE_SIZE"
+	envReporterFlushInterval  = "JAEGER_REPORTER_FLUSH_INTERVAL"
+	envReporterLogSpans       = "JAEGER_REPORTER_LOG_SPANS"
+	envAgentHost              = "JAEGER_AGENT_HOST"
+	envAgentPort              = "JAEGER_AGENT_PORT"
+)
+
+// FromEnv uses environment variables to set the tracer's Configuration
+func FromEnv() (*Configuration, error) {
+	c := &Configuration{}
+
+	if e := os.Getenv(envServiceName); e != "" {
+		c.ServiceName = e
+	}
+
+	if e := os.Getenv(envRPCMetrics); e != "" {
+		if value, err := strconv.ParseBool(e); err == nil {
+			c.RPCMetrics = value
+		} else {
+			return nil, errors.Wrapf(err, "cannot parse env var %s=%s", envRPCMetrics, e)
+		}
+	}
+
+	if e := os.Getenv(envDisabled); e != "" {
+		if value, err := strconv.ParseBool(e); err == nil {
+			c.Disabled = value
+		} else {
+			return nil, errors.Wrapf(err, "cannot parse env var %s=%s", envDisabled, e)
+		}
+	}
+
+	if e := os.Getenv(envTags); e != "" {
+		c.Tags = parseTags(e)
+	}
+
+	if s, err := samplerConfigFromEnv(); err == nil {
+		c.Sampler = s
+	} else {
+		return nil, errors.Wrap(err, "cannot obtain sampler config from env")
+	}
+
+	if r, err := reporterConfigFromEnv(); err == nil {
+		c.Reporter = r
+	} else {
+		return nil, errors.Wrap(err, "cannot obtain reporter config from env")
+	}
+
+	return c, nil
+}
+
+// samplerConfigFromEnv creates a new SamplerConfig based on the environment variables
+func samplerConfigFromEnv() (*SamplerConfig, error) {
+	sc := &SamplerConfig{}
+
+	if e := os.Getenv(envSamplerType); e != "" {
+		sc.Type = e
+	}
+
+	if e := os.Getenv(envSamplerParam); e != "" {
+		if value, err := strconv.ParseFloat(e, 64); err == nil {
+			sc.Param = value
+		} else {
+			return nil, errors.Wrapf(err, "cannot parse env var %s=%s", envSamplerParam, e)
+		}
+	}
+
+	if e := os.Getenv(envSamplerManagerHostPort); e != "" {
+		sc.SamplingServerURL = e
+	}
+
+	if e := os.Getenv(envSamplerMaxOperations); e != "" {
+		if value, err := strconv.ParseInt(e, 10, 0); err == nil {
+			sc.MaxOperations = int(value)
+		} else {
+			return nil, errors.Wrapf(err, "cannot parse env var %s=%s", envSamplerMaxOperations, e)
+		}
+	}
+
+	if e := os.Getenv(envSamplerRefreshInterval); e != "" {
+		if value, err := time.ParseDuration(e); err == nil {
+			sc.SamplingRefreshInterval = value
+		} else {
+			return nil, errors.Wrapf(err, "cannot parse env var %s=%s", envSamplerRefreshInterval, e)
+		}
+	}
+
+	return sc, nil
+}
+
+// reporterConfigFromEnv creates a new ReporterConfig based on the environment variables
+func reporterConfigFromEnv() (*ReporterConfig, error) {
+	rc := &ReporterConfig{}
+
+	if e := os.Getenv(envReporterMaxQueueSize); e != "" {
+		if value, err := strconv.ParseInt(e, 10, 0); err == nil {
+			rc.QueueSize = int(value)
+		} else {
+			return nil, errors.Wrapf(err, "cannot parse env var %s=%s", envReporterMaxQueueSize, e)
+		}
+	}
+
+	if e := os.Getenv(envReporterFlushInterval); e != "" {
+		if value, err := time.ParseDuration(e); err == nil {
+			rc.BufferFlushInterval = value
+		} else {
+			return nil, errors.Wrapf(err, "cannot parse env var %s=%s", envReporterFlushInterval, e)
+		}
+	}
+
+	if e := os.Getenv(envReporterLogSpans); e != "" {
+		if value, err := strconv.ParseBool(e); err == nil {
+			rc.LogSpans = value
+		} else {
+			return nil, errors.Wrapf(err, "cannot parse env var %s=%s", envReporterLogSpans, e)
+		}
+	}
+
+	host := jaeger.DefaultUDPSpanServerHost
+	if e := os.Getenv(envAgentHost); e != "" {
+		host = e
+	}
+
+	port := jaeger.DefaultUDPSpanServerPort
+	if e := os.Getenv(envAgentPort); e != "" {
+		if value, err := strconv.ParseInt(e, 10, 0); err == nil {
+			port = int(value)
+		} else {
+			return nil, errors.Wrapf(err, "cannot parse env var %s=%s", envAgentPort, e)
+		}
+	}
+
+	// the side effect of this is that we are building the default value, even if none of the env vars
+	// were not explicitly passed
+	rc.LocalAgentHostPort = fmt.Sprintf("%s:%d", host, port)
+
+	return rc, nil
+}
+
+// parseTags parses the given string into a collection of Tags.
+// Spec for this value:
+// - comma separated list of key=value
+// - value can be specified using the notation ${envVar:defaultValue}, where `envVar`
+// is an environment variable and `defaultValue` is the value to use in case the env var is not set
+func parseTags(sTags string) []opentracing.Tag {
+	pairs := strings.Split(sTags, ",")
+	tags := make([]opentracing.Tag, 0)
+	for _, p := range pairs {
+		kv := strings.SplitN(p, "=", 2)
+		k, v := strings.TrimSpace(kv[0]), strings.TrimSpace(kv[1])
+
+		if strings.HasPrefix(v, "${") && strings.HasSuffix(v, "}") {
+			ed := strings.SplitN(v[2:len(v)-1], ":", 2)
+			e, d := ed[0], ed[1]
+			v = os.Getenv(e)
+			if v == "" && d != "" {
+				v = d
+			}
+		}
+
+		tag := opentracing.Tag{Key: k, Value: v}
+		tags = append(tags, tag)
+	}
+
+	return tags
+}

vendor/github.com/uber/jaeger-client-go/config/options.go

@@ -0,0 +1,148 @@
+// Copyright (c) 2017 Uber Technologies, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package config
+
+import (
+	opentracing "github.com/opentracing/opentracing-go"
+	"github.com/uber/jaeger-lib/metrics"
+
+	"github.com/uber/jaeger-client-go"
+)
+
+// Option is a function that sets some option on the client.
+type Option func(c *Options)
+
+// Options control behavior of the client.
+type Options struct {
+	metrics             metrics.Factory
+	logger              jaeger.Logger
+	reporter            jaeger.Reporter
+	sampler             jaeger.Sampler
+	contribObservers    []jaeger.ContribObserver
+	observers           []jaeger.Observer
+	gen128Bit           bool
+	zipkinSharedRPCSpan bool
+	maxTagValueLength   int
+	tags                []opentracing.Tag
+	injectors           map[interface{}]jaeger.Injector
+	extractors          map[interface{}]jaeger.Extractor
+}
+
+// Metrics creates an Option that initializes Metrics in the tracer,
+// which is used to emit statistics about spans.
+func Metrics(factory metrics.Factory) Option {
+	return func(c *Options) {
+		c.metrics = factory
+	}
+}
+
+// Logger can be provided to log Reporter errors, as well as to log spans
+// if Reporter.LogSpans is set to true.
+func Logger(logger jaeger.Logger) Option {
+	return func(c *Options) {
+		c.logger = logger
+	}
+}
+
+// Reporter can be provided explicitly to override the configuration.
+// Useful for testing, e.g. by passing InMemoryReporter.
+func Reporter(reporter jaeger.Reporter) Option {
+	return func(c *Options) {
+		c.reporter = reporter
+	}
+}
+
+// Sampler can be provided explicitly to override the configuration.
+func Sampler(sampler jaeger.Sampler) Option {
+	return func(c *Options) {
+		c.sampler = sampler
+	}
+}
+
+// Observer can be registered with the Tracer to receive notifications about new Spans.
+func Observer(observer jaeger.Observer) Option {
+	return func(c *Options) {
+		c.observers = append(c.observers, observer)
+	}
+}
+
+// ContribObserver can be registered with the Tracer to recieve notifications
+// about new spans.
+func ContribObserver(observer jaeger.ContribObserver) Option {
+	return func(c *Options) {
+		c.contribObservers = append(c.contribObservers, observer)
+	}
+}
+
+// Gen128Bit specifies whether to generate 128bit trace IDs.
+func Gen128Bit(gen128Bit bool) Option {
+	return func(c *Options) {
+		c.gen128Bit = gen128Bit
+	}
+}
+
+// ZipkinSharedRPCSpan creates an option that enables sharing span ID between client
+// and server spans a la zipkin. If false, client and server spans will be assigned
+// different IDs.
+func ZipkinSharedRPCSpan(zipkinSharedRPCSpan bool) Option {
+	return func(c *Options) {
+		c.zipkinSharedRPCSpan = zipkinSharedRPCSpan
+	}
+}
+
+// MaxTagValueLength can be provided to override the default max tag value length.
+func MaxTagValueLength(maxTagValueLength int) Option {
+	return func(c *Options) {
+		c.maxTagValueLength = maxTagValueLength
+	}
+}
+
+// Tag creates an option that adds a tracer-level tag.
+func Tag(key string, value interface{}) Option {
+	return func(c *Options) {
+		c.tags = append(c.tags, opentracing.Tag{Key: key, Value: value})
+	}
+}
+
+// Injector registers an Injector with the given format.
+func Injector(format interface{}, injector jaeger.Injector) Option {
+	return func(c *Options) {
+		c.injectors[format] = injector
+	}
+}
+
+// Extractor registers an Extractor with the given format.
+func Extractor(format interface{}, extractor jaeger.Extractor) Option {
+	return func(c *Options) {
+		c.extractors[format] = extractor
+	}
+}
+
+func applyOptions(options ...Option) Options {
+	opts := Options{
+		injectors:  make(map[interface{}]jaeger.Injector),
+		extractors: make(map[interface{}]jaeger.Extractor),
+	}
+	for _, option := range options {
+		option(&opts)
+	}
+	if opts.metrics == nil {
+		opts.metrics = metrics.NullFactory
+	}
+	if opts.logger == nil {
+		opts.logger = jaeger.NullLogger
+	}
+	return opts
+}