prometheus/retrieval/target.go
Julius Volz a1ba23038e Fix scrape timestamps to reduce sample time jitter.
We're currently timestamping samples with the time at the end of a scrape
iteration. It makes more sense to use a timestamp from the beginning of the
scrape for two reasons:

a) this time is more relevant to the scraped values than the time at the
   end of the HTTP-GET + JSON decoding work.
b) it reduces sample timestamp jitter if we measure at the beginning, and
   not at the completion of a scrape.
2013-04-13 03:45:37 +02:00

254 lines
7.2 KiB
Go

// Copyright 2013 Prometheus Team
// 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 retrieval
import (
"fmt"
"github.com/prometheus/client_golang/metrics"
"github.com/prometheus/prometheus/model"
"github.com/prometheus/prometheus/retrieval/format"
"log"
"net/http"
"os"
"strings"
"time"
)
const (
instance = "instance"
)
var (
localhostRepresentations = []string{"http://127.0.0.1", "http://localhost"}
)
// The state of the given Target.
type TargetState int
func (t TargetState) String() string {
switch t {
case UNKNOWN:
return "UNKNOWN"
case ALIVE:
return "ALIVE"
case UNREACHABLE:
return "UNREACHABLE"
}
panic("unknown state")
}
const (
// The Target has not been seen; we know nothing about it, except that it is
// on our docket for examination.
UNKNOWN TargetState = iota
// The Target has been found and successfully queried.
ALIVE
// The Target was either historically found or not found and then determined
// to be unhealthy by either not responding or disappearing.
UNREACHABLE
)
// A healthReporter is a type that can provide insight into its health state.
//
// It mainly exists for testability reasons to decouple the scheduler behaviors
// from fully-fledged Target and other types.
type healthReporter interface {
// Report the last-known health state for this target.
State() TargetState
}
// A Target represents an endpoint that should be interrogated for metrics.
//
// The protocol described by this type will likely change in future iterations,
// as it offers no good support for aggregated targets and fan out. Thusly,
// it is likely that the current Target and target uses will be
// wrapped with some resolver type.
//
// For the future, the Target protocol will abstract away the exact means that
// metrics are retrieved and deserialized from the given instance to which it
// refers.
type Target interface {
// Retrieve values from this target.
//
// earliest refers to the soonest available opportunity to reschedule the
// target for a future retrieval. It is up to the underlying scheduler type,
// alluded to in the scheduledFor function, to use this as it wants to. The
// current use case is to create a common batching time for scraping multiple
// Targets in the future through the TargetPool.
Scrape(earliest time.Time, results chan format.Result) error
// Fulfill the healthReporter interface.
State() TargetState
// Report the soonest time at which this Target may be scheduled for
// retrieval. This value needn't convey that the operation occurs at this
// time, but it should occur no sooner than it.
//
// Right now, this is used as the sorting key in TargetPool.
scheduledFor() time.Time
// The address to which the Target corresponds. Out of all of the available
// points in this interface, this one is the best candidate to change given
// the ways to express the endpoint.
Address() string
// The address as seen from other hosts. References to localhost are resolved
// to the address of the prometheus server.
GlobalAddress() string
// Return the target's base labels.
BaseLabels() model.LabelSet
// Merge a new externally supplied target definition (e.g. with changed base
// labels) into an old target definition for the same endpoint. Preserve
// remaining information - like health state - from the old target.
Merge(newTarget Target)
}
// target is a Target that refers to a singular HTTP or HTTPS endpoint.
type target struct {
// scheduler provides the scheduling strategy that is used to formulate what
// is returned in Target.scheduledFor.
scheduler scheduler
state TargetState
address string
// What is the deadline for the HTTP or HTTPS against this endpoint.
Deadline time.Duration
// Any base labels that are added to this target and its metrics.
baseLabels model.LabelSet
}
// Furnish a reasonably configured target for querying.
func NewTarget(address string, deadline time.Duration, baseLabels model.LabelSet) Target {
target := &target{
address: address,
Deadline: deadline,
baseLabels: baseLabels,
}
scheduler := &healthScheduler{
target: target,
}
target.scheduler = scheduler
return target
}
func (t *target) Scrape(earliest time.Time, results chan format.Result) (err error) {
defer func() {
futureState := t.state
switch err {
case nil:
futureState = ALIVE
default:
futureState = UNREACHABLE
}
t.scheduler.Reschedule(earliest, futureState)
t.state = futureState
}()
done := make(chan bool)
request := func() {
defer func() {
done <- true
}()
now := time.Now()
var resp *http.Response // Don't shadow "err" from the enclosing function.
resp, err = http.Get(t.Address())
if err != nil {
return
}
defer resp.Body.Close()
processor, err := format.DefaultRegistry.ProcessorForRequestHeader(resp.Header)
if err != nil {
return
}
// XXX: This is a wart; we need to handle this more gracefully down the
// road, especially once we have service discovery support.
baseLabels := model.LabelSet{instance: model.LabelValue(t.Address())}
for baseLabel, baseValue := range t.baseLabels {
baseLabels[baseLabel] = baseValue
}
err = processor.Process(resp.Body, now, baseLabels, results)
if err != nil {
return
}
}
accumulator := func(d time.Duration) {
ms := float64(d) / float64(time.Millisecond)
labels := map[string]string{address: t.Address(), outcome: success}
if err != nil {
labels[outcome] = failure
}
targetOperationLatencies.Add(labels, ms)
targetOperations.Increment(labels)
}
go metrics.InstrumentCall(request, accumulator)
select {
case <-done:
break
case <-time.After(t.Deadline):
err = fmt.Errorf("Target %s exceeded %s deadline.", t, t.Deadline)
}
return
}
func (t target) State() TargetState {
return t.state
}
func (t target) scheduledFor() time.Time {
return t.scheduler.ScheduledFor()
}
func (t target) Address() string {
return t.address
}
func (t target) GlobalAddress() string {
address := t.address
hostname, err := os.Hostname()
if err != nil {
log.Printf("Couldn't get hostname: %s, returning target.Address()")
return address
}
for _, localhostRepresentation := range localhostRepresentations {
address = strings.Replace(address, localhostRepresentation, fmt.Sprintf("http://%s", hostname), -1)
}
return address
}
func (t target) BaseLabels() model.LabelSet {
return t.baseLabels
}
// Merge a new externally supplied target definition (e.g. with changed base
// labels) into an old target definition for the same endpoint. Preserve
// remaining information - like health state - from the old target.
func (t *target) Merge(newTarget Target) {
if t.Address() != newTarget.Address() {
panic("targets don't refer to the same endpoint")
}
t.baseLabels = newTarget.BaseLabels()
}