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/sampler_options.go

@@ -0,0 +1,81 @@
+// 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 jaeger
+
+import (
+	"time"
+)
+
+// SamplerOption is a function that sets some option on the sampler
+type SamplerOption func(options *samplerOptions)
+
+// SamplerOptions is a factory for all available SamplerOption's
+var SamplerOptions samplerOptions
+
+type samplerOptions struct {
+	metrics                 *Metrics
+	maxOperations           int
+	sampler                 Sampler
+	logger                  Logger
+	samplingServerURL       string
+	samplingRefreshInterval time.Duration
+}
+
+// Metrics creates a SamplerOption that initializes Metrics on the sampler,
+// which is used to emit statistics.
+func (samplerOptions) Metrics(m *Metrics) SamplerOption {
+	return func(o *samplerOptions) {
+		o.metrics = m
+	}
+}
+
+// MaxOperations creates a SamplerOption that sets the maximum number of
+// operations the sampler will keep track of.
+func (samplerOptions) MaxOperations(maxOperations int) SamplerOption {
+	return func(o *samplerOptions) {
+		o.maxOperations = maxOperations
+	}
+}
+
+// InitialSampler creates a SamplerOption that sets the initial sampler
+// to use before a remote sampler is created and used.
+func (samplerOptions) InitialSampler(sampler Sampler) SamplerOption {
+	return func(o *samplerOptions) {
+		o.sampler = sampler
+	}
+}
+
+// Logger creates a SamplerOption that sets the logger used by the sampler.
+func (samplerOptions) Logger(logger Logger) SamplerOption {
+	return func(o *samplerOptions) {
+		o.logger = logger
+	}
+}
+
+// SamplingServerURL creates a SamplerOption that sets the sampling server url
+// of the local agent that contains the sampling strategies.
+func (samplerOptions) SamplingServerURL(samplingServerURL string) SamplerOption {
+	return func(o *samplerOptions) {
+		o.samplingServerURL = samplingServerURL
+	}
+}
+
+// SamplingRefreshInterval creates a SamplerOption that sets how often the
+// sampler will poll local agent for the appropriate sampling strategy.
+func (samplerOptions) SamplingRefreshInterval(samplingRefreshInterval time.Duration) SamplerOption {
+	return func(o *samplerOptions) {
+		o.samplingRefreshInterval = samplingRefreshInterval
+	}
+}