[tmpnet] Set an explicit instance label for logs and metrics

Previously, the configuuration for promtail and prometheus did not set
an explicit `instance` label. This resulted in the default of `ip:port`
being used, and since that could change on restart, it was necessary
to try to ensure a stable port. Setting an explicit and unique value
for `instance` avoids needing to ensure a stable port.

tests/fixture/tmpnet/network.go

@@ -510,23 +510,6 @@ func (n *Network) StartNode(ctx context.Context, log logging.Logger, node *Node)
 
 // Restart a single node.
 func (n *Network) RestartNode(ctx context.Context, log logging.Logger, node *Node) error {
-	// Ensure the node reuses the same API port across restarts to ensure
-	// consistent labeling of metrics. Otherwise prometheus's automatic
-	// addition of the `instance` label (host:port) results in
-	// segmentation of results for a given node every time the port
-	// changes on restart. This segmentation causes graphs on the grafana
-	// dashboards to display multiple series per graph for a given node,
-	// one for each port that the node used.
-	//
-	// There is a non-zero chance of the port being allocatted to a
-	// different process and the node subsequently being unable to start,
-	// but the alternative is having to update the grafana dashboards
-	// query-by-query to ensure that node metrics ignore the instance
-	// label.
-	if err := node.SaveAPIPort(); err != nil {
-		return err
-	}
-
 	if err := node.Stop(ctx); err != nil {
 		return fmt.Errorf("failed to stop node %s: %w", node.NodeID, err)
 	}

tests/fixture/tmpnet/node.go

@@ -9,7 +9,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"net"
 	"net/http"
 	"net/netip"
 	"os"
@@ -366,19 +365,10 @@ func (n *Node) EnsureNodeID() error {
 	return nil
 }
 
-// Saves the currently allocated API port to the node's configuration
-// for use across restarts. Reusing the port ensures consistent
-// labeling of metrics.
-func (n *Node) SaveAPIPort() error {
-	hostPort := strings.TrimPrefix(n.URI, "http://")
-	if len(hostPort) == 0 {
-		// Without an API URI there is nothing to save
-		return nil
-	}
-	_, port, err := net.SplitHostPort(hostPort)
-	if err != nil {
-		return err
-	}
-	n.Flags[config.HTTPPortKey] = port
-	return nil
+// GetUniqueID returns a globally unique identifier for the node.
+func (n *Node) GetUniqueID() string {
+	nodeIDString := n.NodeID.String()
+	startIndex := len(ids.NodeIDPrefix)
+	endIndex := startIndex + 8 // 8 characters should be enough to identify a node in the context of its network
+	return n.NetworkUUID + "-" + strings.ToLower(nodeIDString[startIndex:endIndex])
 }

tests/fixture/tmpnet/node_process.go

@@ -247,6 +247,10 @@ func (p *NodeProcess) getProcess() (*os.Process, error) {
 func (p *NodeProcess) writeMonitoringConfig() error {
 	// Ensure labeling that uniquely identifies the node and its network
 	commonLabels := FlagsMap{
+		// Explicitly setting a instance label avoids the use of the
+		// node's URI which may change on restart and preclude the
+		// continuity of collected metrics.
+		"instance":          p.node.GetUniqueID(),
 		"network_uuid":      p.node.NetworkUUID,
 		"node_id":           p.node.NodeID,
 		"is_ephemeral_node": strconv.FormatBool(p.node.IsEphemeral),