refactor: consolidate metric collection into single SSH calls and add support for SSH key authentication

bin/collect_metrics.php

@@ -25,15 +25,27 @@ ini_set('display_errors', 1);
 ini_set('log_errors', 1);
 ini_set('error_log', '/var/log/metrics_collector_errors.log');
 
+// Prevent multiple instances using flock (#42)
+$lockFile = '/var/run/collect_metrics.lock';
+$lockFp = fopen($lockFile, 'w');
+if (!$lockFp || !flock($lockFp, LOCK_EX | LOCK_NB)) {
+    echo "[" . date('Y-m-d H:i:s') . "] Another collector instance is already running. Exiting.\n";
+    exit(0);
+}
+
 // Write PID file for monitoring
 $pidFile = '/var/run/collect_metrics.pid';
 file_put_contents($pidFile, getmypid());
 
-// Register shutdown function to clean up PID file
-register_shutdown_function(function() use ($pidFile) {
+// Register shutdown function to clean up PID and lock files
+register_shutdown_function(function() use ($pidFile, $lockFp, $lockFile) {
     if (file_exists($pidFile)) {
         unlink($pidFile);
     }
+    if ($lockFp) {
+        flock($lockFp, LOCK_UN);
+        fclose($lockFp);
+    }
 });
 
 echo "[" . date('Y-m-d H:i:s') . "] Metrics collector started (PID: " . getmypid() . ")\n";

bin/monitor_metrics.sh

@@ -2,15 +2,24 @@
 
 # Monitor and restart metrics collector if it's not running
 # This script checks if collect_metrics.php is running and restarts it if needed
+# Uses flock to prevent multiple instances (#42)
 
 SCRIPT_PATH="/var/www/html/bin/collect_metrics.php"
 LOG_FILE="/var/log/metrics_monitor.log"
 PID_FILE="/var/run/collect_metrics.pid"
+LOCK_FILE="/var/run/collect_metrics.lock"
 
 log_message() {
     echo "[$(date '+%Y-%m-%d %H:%M:%S')] $1" >> "$LOG_FILE"
 }
 
+# Use flock to prevent multiple monitor instances
+exec 200>"$LOCK_FILE"
+if ! flock -n 200; then
+    log_message "Another monitor instance is running, exiting"
+    exit 0
+fi
+
 # Check if the process is running
 is_running() {
     if [ -f "$PID_FILE" ]; then
@@ -22,6 +31,12 @@ is_running() {
             fi
         fi
     fi
+    # Also check if any collect_metrics.php is running (catches orphan processes)
+    if pgrep -f "collect_metrics.php" > /dev/null 2>&1; then
+        # Update PID file with actual PID
+        pgrep -f "collect_metrics.php" | head -1 > "$PID_FILE"
+        return 0
+    fi
     return 1
 }