Remember and display last scrape errors in web UI.

retrieval/target.go

@@ -90,6 +90,8 @@ type Target interface {
 	//
 	// Right now, this is used as the sorting key in TargetPool.
 	scheduledFor() time.Time
+	// Return the last encountered scrape error, if any.
+	LastError() error
 	// 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.
@@ -110,14 +112,18 @@ type target struct {
 	// scheduler provides the scheduling strategy that is used to formulate what
 	// is returned in Target.scheduledFor.
 	scheduler scheduler
-	state     TargetState
+	// The current health state of the target.
+	state TargetState
+	// The last encountered scrape error, if any.
+	lastError error
 
 	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
-	client     http.Client
+	// The HTTP client used to scrape the target's endpoint.
+	client http.Client
 }
 
 // Furnish a reasonably configured target for querying.
@@ -176,6 +182,7 @@ func (t *target) Scrape(earliest time.Time, results chan format.Result) (err err
 
 	t.scheduler.Reschedule(earliest, futureState)
 	t.state = futureState
+	t.lastError = err
 
 	return err
 }
@@ -221,6 +228,10 @@ func (t target) scheduledFor() time.Time {
 	return t.scheduler.ScheduledFor()
 }
 
+func (t target) LastError() error {
+	return t.lastError
+}
+
 func (t target) Address() string {
 	return t.address
 }

retrieval/targetmanager_test.go

@@ -31,6 +31,10 @@ type fakeTarget struct {
 	scheduleIndex int
 }
 
+func (t fakeTarget) LastError() error {
+	return nil
+}
+
 func (t fakeTarget) Address() string {
 	return "fake"
 }

web/static/css/prometheus.css

@@ -82,4 +82,10 @@ input[name=end_input], input[name=range_input] {
 
 .literal_output td {
   font-family: monospace;
-}
+}
+
+.error_text {
+  background-color: #f2dede;
+  border: 1px solid #c0a0a0;
+  padding: 0 2px 0 2px;
+}

web/templates/status.html

@@ -36,6 +36,10 @@
               {{range $pool.Targets}}
                 <li>
                 <a href="{{.GlobalAddress}}">{{.Address}}</a> (State: {{.State}}, Base Labels: {{.BaseLabels}})
+                {{if .LastError}}
+                <br/>
+                <span class="error_text"><b>Scrape error:</b> "{{.LastError}}"</span>
+                {{end}}
                 </li>
               {{end}}
             </ul>