Troubleshooting Azure Virtual Machines

Common Issues and Solutions

This section provides guidance on identifying and resolving common problems encountered with Azure Virtual Machines. We cover a range of scenarios, from connectivity issues to performance bottlenecks.

Connectivity Problems

Issues preventing your VM from connecting to the internet or other resources:

Performance Degradation

Slow performance can impact application responsiveness. Here are common causes:

Boot and Startup Failures

When your virtual machine fails to boot or starts with errors:

Application-Specific Issues

Troubleshooting problems related to specific applications running on your VMs:

Network Security Group (NSG) Misconfigurations

NSGs control network traffic to and from Azure resources. Incorrectly configured rules can block legitimate traffic.

Common Scenarios:

Troubleshooting Steps:

  1. Review NSG Rules: Navigate to your VM's Network Interface or the associated NSG resource in the Azure portal. Carefully examine both inbound and outbound security rules.
  2. Check Effective Rules: Use the "Effective security rules" blade on the Network Security Group to see the combined effect of all applied NSGs (on the NIC and subnet).
  3. Test Connectivity: Use tools like `telnet`, `psping`, or `tcpping` from another VM or your local machine to test connectivity to the VM's IP and port.
  4. Temporarily Loosen Rules: As a diagnostic step, temporarily allow all inbound traffic from your IP to the VM and see if connectivity is restored. Remember to re-secure your NSG afterward.

Note: For RDP and SSH, ensure you also have appropriate Network Address Translation (NAT) rules if using a Load Balancer or Application Gateway.

On-VM Firewall Rules

Firewalls configured directly on the operating system (Windows Firewall, iptables) can also block traffic.

Troubleshooting Steps:

  1. Connect to your VM via RDP or SSH.
  2. Check the status and rules of your OS firewall.
  3. Temporarily disable the firewall to see if connectivity is restored.
  4. If disabling the firewall resolves the issue, re-enable it and add specific rules to allow the required traffic.

DNS Resolution Issues

Problems resolving hostnames can prevent applications from reaching external services or even Azure resources.

Troubleshooting Steps:

  1. From the VM, try pinging an IP address (e.g., 8.8.8.8) and a hostname (e.g., google.com).
  2. If pinging an IP works but a hostname doesn't, it's likely a DNS issue.
  3. Verify your VM's DNS settings (usually configured via DHCP from Azure's DNS or a custom DNS server).
  4. Check your Azure Virtual Network's DNS settings.
  5. Ensure your custom DNS servers are reachable from the VM.

High CPU Utilization

Sustained high CPU usage can make a VM unresponsive.

Troubleshooting Steps:

  1. Monitor CPU: Use Azure Monitor or Task Manager/`top` command on the VM to identify processes consuming high CPU.
  2. Analyze Processes: Investigate the identified processes. Is it a known application, a background service, or potentially malware?
  3. Check for Updates: Ensure applications and the OS are up-to-date, as performance improvements are often included in patches.
  4. Optimize Applications: Review application code or configuration for inefficiencies.
  5. Scale Up: If the workload legitimately requires more processing power, consider resizing the VM to a larger instance type.

Tip: Azure's VM Insights can provide detailed performance metrics and recommendations.

Disk I/O Bottlenecks (IOPS)

When disk read/write operations are slow, impacting application performance.

Troubleshooting Steps:

  1. Monitor Disk Metrics: Use Azure Monitor to check Disk Read IOPS, Disk Write IOPS, Disk Read Bytes, Disk Write Bytes, and Disk Queue Length.
  2. Analyze Workload: Identify applications or processes generating high disk I/O.
  3. Choose Appropriate Disk Type: Ensure your VM's disks (OS disk, data disks) are of a performance tier (e.g., Standard SSD, Premium SSD, Ultra Disk) that matches your workload requirements.
  4. Optimize Disk Usage: Defragment disks, clean up temporary files, and move frequently accessed data to faster disks.
  5. Consider More Disks: For some workloads, spreading I/O across multiple data disks can improve performance.

Resources for Deeper Dives

When the common solutions don't resolve your issue, explore these resources: