Add a prometheus HTTP server per ignite-spawn process in an unix socket

cmd/ignite-spawn/ignite-spawn.go

@@ -3,8 +3,10 @@ package main
 import (
 	"fmt"
 	"os"
+	"path"
 
 	"github.com/weaveworks/ignite/pkg/container"
+	"github.com/weaveworks/ignite/pkg/container/prometheus"
 	"github.com/weaveworks/ignite/pkg/metadata/loader"
 	"github.com/weaveworks/ignite/pkg/metadata/vmmd"
 )
@@ -43,6 +45,10 @@ func StartVM(co *options) error {
 		return err
 	}
 
+	// Serve metrics over an unix socket in the VM's own directory
+	metricsSocket := path.Join(co.vm.ObjectPath(), "prometheus.sock")
+	go prometheus.ServeMetrics(metricsSocket)
+
 	// VM state handling
 	if err := co.vm.SetState(vmmd.Running); err != nil {
 		return fmt.Errorf("failed to update VM state: %v", err)

pkg/container/prometheus/server.go

@@ -0,0 +1,30 @@
+package prometheus
+
+import (
+	"net/http"
+	"net"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+func ServeMetrics(socketPath string) error {
+	// Create a registry to register metrics into
+	registry := prometheus.NewRegistry()
+	// Register the default collectors with this registry
+	registry.MustRegister(prometheus.NewBuildInfoCollector())
+	registry.MustRegister(prometheus.NewGoCollector())
+	registry.MustRegister(prometheus.NewProcessCollector(prometheus.ProcessCollectorOpts{}))
+
+	// Create a HTTP server to handle metrics requests
+	server := http.Server{
+		Handler: promhttp.HandlerFor(registry, promhttp.HandlerOpts{}),
+	}
+
+	// Listen on the unix socket and serve the web server
+	unixListener, err := net.Listen("unix", socketPath)
+	if err != nil {
+		panic(err)
+	}
+	return server.Serve(unixListener)
+}