opentracing -> opencensus (#802)

* update vendor directory, add go.opencensus.io

* update imports

* oops

* s/opentracing/opencensus/ & remove prometheus / zipkin stuff & remove old stats

* the dep train rides again

* fix gin build

* deps from last guy

* start in on the agent metrics

* she builds

* remove tags for now, cardinality error is fussing. subscribe instead of register

* update to patched version of opencensus to proceed for now TODO switch to a release

* meh

fix imports

* println debug the bad boys

* lace it with the tags

* update deps again

* fix all inconsistent cardinality errors

* add our own logger

* fix init

* fix oom measure

* remove bugged removal code

* fix s3 measures

* fix prom handler nil

api/common/ctx.go

@@ -4,6 +4,8 @@ import (
 	"context"
 
 	"github.com/sirupsen/logrus"
+	"go.opencensus.io/tag"
+	"go.opencensus.io/trace"
 )
 
 type contextKey string
@@ -22,11 +24,35 @@ func Logger(ctx context.Context) logrus.FieldLogger {
 	return l
 }
 
-// Attempt at simplifying this whole logger in the context thing
-// Could even make this take a generic map, then the logger that gets returned could be used just like the stdlib too, since it's compatible
+// LoggerWithFields returns a child context of the provided parent that
+// contains a logger with additional fields from the parent's logger, it
+// returns the new child logger, as well.
 func LoggerWithFields(ctx context.Context, fields logrus.Fields) (context.Context, logrus.FieldLogger) {
 	l := Logger(ctx)
 	l = l.WithFields(fields)
 	ctx = WithLogger(ctx, l)
 	return ctx, l
 }
+
+// BackgroundContext returns a context that is specifically not a child of the
+// provided parent context wrt any cancellation or deadline of the parent,
+// returning a context that contains all values only. At present, this is a
+// best effort as there is not a great way to extract all values, known values:
+// * logger
+// * span
+// * tags
+// (TODO(reed): we could have our own context.Context implementer that stores
+// all values from WithValue in a bucket we could extract more easily?)
+func BackgroundContext(ctx context.Context) context.Context {
+	logger := Logger(ctx)
+	span := trace.FromContext(ctx)
+	tagMap := tag.FromContext(ctx)
+
+	// fresh context
+	ctx = context.Background()
+
+	ctx = tag.NewContext(ctx, tagMap)
+	ctx = trace.WithSpan(ctx, span)
+	ctx = WithLogger(ctx, logger)
+	return ctx
+}