Prometheus on a node; panel under a URL prefix; open ports on migrate import

A panel without VPN (e.g. after the move) can use a Prometheus that lives on
a node, such as the one with history left on the old server (node #0). Both
directions go through the agent's WSS: the node's Prometheus scrapes
127.0.0.1:AGENT_METRICS_PORT/metrics, the agent checks its token and asks
core (metrics → metrics_res, the same exposition as /metrics, at most once
per 5 s per connection); the monitor tab reads it back through the agent,
which forwards only GET /-/ready and /api/v1/query[_range]. The panel finds
it by itself (local first, then the lowest-id node), and the install/remove
buttons work on a panel without VPN. `monitor install` on a node without its
own panel picks AGENT_METRICS_PORT, writes it to cli.env and restarts the
agent; on the old server it keeps the collected data.

The panel works behind nginx in a subfolder: relative asset and API paths,
relative directory redirects, and the client address from X-Forwarded-For /
X-Real-IP only from trusted proxies (loopback, TRUST_PROXY).

migrate import opens the moved SUB_PORT/NODE_PORT in UFW when it is active.

internal/migrate/migrate_test.go

@@ -4,6 +4,7 @@ import (
 	"archive/tar"
 	"bytes"
 	"compress/gzip"
+	"errors"
 	"os"
 	"path/filepath"
 	"regexp"
@@ -174,3 +175,31 @@ func TestCodeAndSeal(t *testing.T) {
 		t.Error("открылся повреждённый")
 	}
 }
+
+// Приём переноса открывает новые порты в UFW, только если он активен, — как install.sh.
+func TestOpenFirewall(t *testing.T) {
+	var calls []string
+	status := "Status: active"
+	defer func(f func(...string) ([]byte, error)) { ufw = f }(ufw)
+	ufw = func(args ...string) ([]byte, error) {
+		calls = append(calls, strings.Join(args, " "))
+		if args[0] == "status" {
+			return []byte(status), nil
+		}
+		if len(args) > 1 && args[1] == "45000/tcp" {
+			return nil, errors.New("exit 1")
+		}
+		return nil, nil
+	}
+	opened, failed := OpenFirewall(40222, 45000, 0)
+	if strings.Join(opened, ",") != "40222/tcp" || strings.Join(failed, ",") != "45000/tcp" {
+		t.Errorf("opened %v failed %v", opened, failed)
+	}
+	if strings.Join(calls, "; ") != "status; allow 40222/tcp; allow 45000/tcp; reload" {
+		t.Errorf("вызовы: %v", calls)
+	}
+	calls, status = nil, "Status: inactive"
+	if opened, _ := OpenFirewall(40222); opened != nil || len(calls) != 1 {
+		t.Errorf("UFW выключен, а правила трогаются: %v", calls)
+	}
+}