report disk usage where the data actually lives

README.md

@@ -19,9 +19,16 @@ docker run -d \
 - STATS_FREQUENCY - default to **30**
 - EVENT_ENDPOINT - default to **http://app:8080/events**
 - HEALTH_CHECK_ENDPOINT - default to **http://app:8080/version**
+- DISK_PATH - mountpoint reported as node disk usage, default to **/** (**\\** on windows)
 - DEBUG_EVENT - default to **false**
 - DEBUG_STATS - default to **false**
 
+The docker client is configured from the standard docker environment variables:
+
+- DOCKER_HOST - docker endpoint, default to the mounted **/var/run/docker.sock**. Set to e.g. **tcp://proxy:2375** to go through a socket proxy instead of mounting the socket
+- DOCKER_API_VERSION - docker api version used by the client. Must be supported by your engine, docker 29 dropped everything below **1.44**
+- DOCKER_CERT_PATH, DOCKER_TLS_VERIFY - tls settings for a remote endpoint
+
 ## Important!
 
 In case you are deploying agent inside Swarmpit [stack](https://github.com/swarmpit/swarmpit/blob/master/docker-compose.yml)

setup/args.go

@@ -14,6 +14,7 @@ type args struct {
 	StatsFrequency      int    `json:"stats_frequency"`
 	EventEndpoint       string `json:"event_endpoint"`
 	HealthCheckEndpoint string `json:"healthcheck_endpoint"`
+	DiskPath            string `json:"disk_path"`
 	Debug               debug  `json:"debug"`
 }
 
@@ -22,6 +23,7 @@ func GetArgs() *args {
 		StatsFrequency:      getIntValue(30, "STATS_FREQUENCY"),
 		EventEndpoint:       getStringValue("http://app:8080/events", "EVENT_ENDPOINT"),
 		HealthCheckEndpoint: getStringValue("http://app:8080/version", "HEALTH_CHECK_ENDPOINT"),
+		DiskPath:            getStringValue("", "DISK_PATH"),
 		Debug: debug{
 			Event: getBooleanValue(false, "DEBUG_EVENT"),
 			Stats: getBooleanValue(false, "DEBUG_STATS")},

swarmpit/task/stats.go

@@ -63,9 +63,20 @@ func getPath() string {
 	return "/"
 }
 
+// diskPath is the mountpoint reported as the node's disk usage. defaults to the
+// platform root, override with DISK_PATH when data lives on another partition.
+func diskPath() string {
+	if arg.DiskPath != "" {
+		return arg.DiskPath
+	}
+	return getPath()
+}
+
 func DiskUsage() (ds DiskStatus) {
-	diskStat, err := disk.Usage(getPath())
+	path := diskPath()
+	diskStat, err := disk.Usage(path)
 	if err != nil {
+		log.Printf("ERROR: Disk usage fetching failed for %s: %s\n", path, err)
 		return
 	}
 

swarmpit/task/stats_test.go

@@ -120,3 +120,49 @@ func TestContainersUsageSurvivesABadContainer(t *testing.T) {
 		t.Fatalf("expected container aaa, got %+v", got[0])
 	}
 }
+
+// DISK_PATH lets a node report the partition its data actually lives on
+// instead of always reporting root. See swarmpit/agent#5.
+func TestDiskPathDefaultsToPlatformRoot(t *testing.T) {
+	original := arg.DiskPath
+	defer func() { arg.DiskPath = original }()
+
+	arg.DiskPath = ""
+	if got := diskPath(); got != getPath() {
+		t.Fatalf("expected the platform root %q, got %q", getPath(), got)
+	}
+}
+
+func TestDiskPathHonoursOverride(t *testing.T) {
+	original := arg.DiskPath
+	defer func() { arg.DiskPath = original }()
+
+	arg.DiskPath = "/mnt/data"
+	if got := diskPath(); got != "/mnt/data" {
+		t.Fatalf("expected /mnt/data, got %q", got)
+	}
+}
+
+func TestDiskUsageReportsTheConfiguredPath(t *testing.T) {
+	original := arg.DiskPath
+	defer func() { arg.DiskPath = original }()
+
+	arg.DiskPath = "/"
+	root := DiskUsage()
+	if root.Total == 0 {
+		t.Fatal("expected a non-zero total for /")
+	}
+	if root.Used+root.Free > root.Total*2 {
+		t.Fatalf("implausible usage figures: %+v", root)
+	}
+}
+
+func TestDiskUsageOnMissingPathIsZeroNotPanic(t *testing.T) {
+	original := arg.DiskPath
+	defer func() { arg.DiskPath = original }()
+
+	arg.DiskPath = "/definitely/not/a/mountpoint"
+	if got := DiskUsage(); got != (DiskStatus{}) {
+		t.Fatalf("expected a zero status for a bad path, got %+v", got)
+	}
+}