[hostmetricsreceiver]: support reporting amount of available CPUs

Signed-off-by: Benedikt Bongartz <bongartz@klimlive.de>

.chloggen/hostmetricsreceiver_support_cpu_count.yaml

@@ -0,0 +1,20 @@
+# Use this changelog template to create an entry for release notes.
+# If your change doesn't affect end users, such as a test fix or a tooling change,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: hostmetricsreceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Report number of CPUs as metric.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [22099]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:

receiver/hostmetricsreceiver/internal/scraper/cpuscraper/cpu_scraper.go

@@ -64,5 +64,15 @@ func (s *scraper) scrape(_ context.Context) (pmetric.Metrics, error) {
 		return pmetric.NewMetrics(), scrapererror.NewPartialScrapeError(err, metricsLen)
 	}
 
+	numCPU, err := cpu.Counts(true)
+	if err != nil {
+		return pmetric.NewMetrics(), scrapererror.NewPartialScrapeError(err, metricsLen)
+	}
+	machineID, err := getMachineID()
+	if err != nil {
+		return pmetric.NewMetrics(), scrapererror.NewPartialScrapeError(err, metricsLen)
+	}
+	s.recordCPUCountDataPoint(now, numCPU, machineID)
+
 	return s.mb.Emit(), nil
 }

receiver/hostmetricsreceiver/internal/scraper/cpuscraper/cpu_scraper_linux.go

@@ -7,6 +7,9 @@
 package cpuscraper // import "github.com/open-telemetry/opentelemetry-collector-contrib/receiver/hostmetricsreceiver/internal/scraper/cpuscraper"
 
 import (
+	"io/ioutil"
+	"strings"
+
 	"github.com/shirou/gopsutil/v3/cpu"
 	"go.opentelemetry.io/collector/pdata/pcommon"
 
@@ -35,3 +38,16 @@ func (s *scraper) recordCPUUtilization(now pcommon.Timestamp, cpuUtilization uca
 	s.mb.RecordSystemCPUUtilizationDataPoint(now, cpuUtilization.Steal, cpuUtilization.CPU, metadata.AttributeStateSteal)
 	s.mb.RecordSystemCPUUtilizationDataPoint(now, cpuUtilization.Iowait, cpuUtilization.CPU, metadata.AttributeStateWait)
 }
+
+func (s *scraper) recordCPUCountDataPoint(now pcommon.Timestamp, count int, machineID string) {
+	s.mb.RecordSystemCPUCountDataPoint(now, int64(count), machineID)
+}
+
+func getMachineID() (string, error) {
+	machineID, err := ioutil.ReadFile("/etc/machine-id")
+	if err != nil {
+		return "", err
+	}
+
+	return strings.TrimSpace(string(machineID)), nil
+}

receiver/hostmetricsreceiver/internal/scraper/cpuscraper/cpu_scraper_others.go

@@ -27,3 +27,9 @@ func (s *scraper) recordCPUUtilization(now pcommon.Timestamp, cpuUtilization uca
 	s.mb.RecordSystemCPUUtilizationDataPoint(now, cpuUtilization.Idle, cpuUtilization.CPU, metadata.AttributeStateIdle)
 	s.mb.RecordSystemCPUUtilizationDataPoint(now, cpuUtilization.Irq, cpuUtilization.CPU, metadata.AttributeStateInterrupt)
 }
+
+func (s *scraper) recordCPUCountDataPoint(now pcommon.Timestamp, count int, machineID string) {}
+
+func getMachineID() (string, error) {
+	return "", nil
+}

receiver/hostmetricsreceiver/internal/scraper/cpuscraper/documentation.md

@@ -37,6 +37,20 @@ metrics:
     enabled: true
 ```
 
+### system.cpu.count
+
+Number of available CPUs.
+
+| Unit | Metric Type | Value Type |
+| ---- | ----------- | ---------- |
+| 1 | Gauge | Int |
+
+#### Attributes
+
+| Name | Description | Values |
+| ---- | ----------- | ------ |
+| machine-id | Machine identifier. | Any Str |
+
 ### system.cpu.utilization
 
 Percentage of CPU time broken down by different states.

receiver/hostmetricsreceiver/internal/scraper/cpuscraper/internal/metadata/testdata/config.yaml

@@ -1,12 +1,16 @@
 default:
 all_set:
   metrics:
+    system.cpu.count:
+      enabled: true
     system.cpu.time:
       enabled: true
     system.cpu.utilization:
       enabled: true
 none_set:
   metrics:
+    system.cpu.count:
+      enabled: false
     system.cpu.time:
       enabled: false
     system.cpu.utilization:

receiver/hostmetricsreceiver/internal/scraper/cpuscraper/metadata.yaml

@@ -12,6 +12,10 @@ attributes:
     type: string
     enum: [idle, interrupt, nice, softirq, steal, system, user, wait]
 
+  machine-id:
+    description: Machine identifier.
+    type: string
+
 metrics:
   system.cpu.time:
     enabled: true
@@ -30,3 +34,11 @@ metrics:
     gauge:
       value_type: double
     attributes: [cpu, state]
+
+  system.cpu.count:
+    enabled: false
+    description: Number of available CPUs.
+    unit: 1
+    gauge:
+      value_type: int
+    attributes: [machine-id]