Knowledge Base

Virtualization technologies form the basis of today's modern data centers and cloud computing infrastructures. Kernel-based Virtual Machine (KVM) is an open-source and powerful virtualization solution built on the Linux kernel. KVM enables the creation, management, and operation of virtual machines (VMs). Live Migration, on the other hand, is the process of transferring a running virtual machine from one physical server to another without any interruption. In this article, we will discuss the intricacies, tips, and best practices of live migration on KVM servers in detail.

1. What is Live Migration? Why is it Important?

1.1. Definition and Basic Principles of Live Migration

Live migration is the process of transferring a running virtual machine from one physical server to another without service interruption. During this process, the VM's memory, processor state, disk data, and network connections are copied to the target server. After the copying process is complete, the VM continues to run on the target server, and users do not notice any interruption.

1.2. Advantages and Use Cases of Live Migration

• System Maintenance and Upgrades: When you need to perform maintenance on servers or upgrade hardware, you can prevent service interruption by migrating VMs to other servers using live migration.
• Load Balancing: By balancing the load between servers, you can ensure more efficient use of resources. You can improve performance by moving VMs from a server under heavy processing load to a less loaded server.
• Energy Saving: You can save energy by turning off less used servers. After moving VMs to active servers, you can reduce energy costs by turning off idle servers.
• High Availability: In the event of a hardware failure, you can ensure that services continue to run continuously by automatically moving VMs to other servers. This minimizes business continuity and data loss.
• Test and Development Environments: You can perform tests based on real data by copying VMs in the production environment to test and development environments with live migration.

1.3. Basic Requirements for Live Migration

• Shared Storage: The disk images of VMs (e.g., QCOW2 files) must be located in a shared storage area (e.g., NFS, iSCSI, GlusterFS) accessible by all servers.
• Network Connectivity: The source and destination servers must be on the same network, and the VM's network configuration (IP address, MAC address) must not change.
• Compatible Processor Architecture: The source and destination servers must have the same processor architecture (e.g., x86_64) or KVM's CPU emulation feature must be used.
• KVM Version: The KVM version on the source and destination servers must be compatible. It is generally recommended to use the same or similar versions.
• Sufficient Resources: The destination server must have sufficient processor, memory, and storage resources to meet the VM's requirements.

2. Types and Methods of Live Migration

2.1. Live Migration with Shared Storage (Shared Storage Migration)

In this method, the disk images of the VM are located in a shared storage area. During live migration, only the VM's memory and processor state are copied to the destination server. Since the disk data is already in the shared storage area, this method is faster and consumes fewer resources.

2.2. Live Migration without Shared Storage (Non-Shared Storage Migration)

In this method, the disk images of the VM are not located in a shared storage area. During live migration, both the VM's memory and disk data are copied to the destination server. This method is slower and consumes more resources, but it can be used in cases where there is no shared storage infrastructure.

2.3. Post-Copy and Pre-Copy Live Migration

• Pre-Copy: In this method, all of the VM's memory is first copied to the destination server. Then, the memory pages that change on the source server are repeatedly copied to the destination server. This process continues until the size of the changing memory pages falls below a certain threshold. Finally, the VM starts running on the destination server. Pre-copy provides high-performance and low-downtime live migration.
• Post-Copy: In this method, as soon as the VM starts running on the destination server, the memory pages on the source server are copied to the destination server as needed. Post-copy provides a faster migration process, but may cause performance degradation during initial accesses.

3. Live Migration with KVM: Step-by-Step Instructions

3.1. Preparing the Environment

1. Shared Storage Setup: Set up and configure a shared storage system such as NFS, iSCSI, or GlusterFS. Move the disk images of the VMs to this storage area.
2. Network Configuration: Ensure that the source and destination servers are on the same network and that the VM's network configuration is correct.
3. KVM Installation and Configuration: Ensure that KVM is installed and configured correctly on the source and destination servers.
4. Libvirt Configuration: Ensure that Libvirt (a tool used to manage KVM) is configured correctly and can access the source and destination servers.

3.2. Performing Live Migration (with virsh command)

To perform a live migration, you can use the virsh migrate command. Here is an example:

virsh migrate --live vm_name qemu+ssh://destination_server_ip_address/system

This command live migrates the virtual machine named "vm_name" to the server at the address "destination_server_ip_address". The --live option specifies the live migration process. The Qemu+ssh protocol provides secure data transfer.

3.3. Performing Live Migration (with virt-manager)

Virt-manager is a graphical interface used to manage KVM virtual machines. To perform a live migration with virt-manager:

1. Open virt-manager and connect to the virtual machine you want to migrate.
2. Right-click on the virtual machine and select the "Migrate" option.
3. Enter the IP address or hostname of the destination server.
4. Specify the migration options (e.g., whether shared storage will be used).
5. Click the "Migrate" button.

3.4. Post-Live Migration Checks

1. Ensure that the VM is running successfully on the destination server.
2. Ensure that the VM's network connection is correct and accessible.
3. Monitor the VM's performance and check for any issues.

4. Factors Affecting Performance and Optimization Methods

4.1. Network Bandwidth and Latency

Network bandwidth and latency significantly affect live migration performance. High bandwidth and low latency provide faster and smoother migration. To optimize your network infrastructure:

• Use 10 Gbps or higher speed network connections.
• Perform live migration between servers located on the same network segment.
• Use Quality of Service (QoS) configuration to prevent network congestion.

4.2. Storage Performance

Storage performance is especially important when performing live migration with non-shared storage. By using high-speed storage systems (e.g., SSDs), you can shorten the migration time. To optimize storage performance:

• Use SSD or NVMe storage.
• Balance the load on the storage system.
• Enable storage cache.

4.3. Memory Management

Memory management plays a crucial role during live migration. To accelerate the memory copying process and minimize downtime:

• Use the pre-copy live migration method.
• Enable memory compression.
• Use Large Page support.

4.4. Processor Usage

Processor usage is important on both source and destination servers during live migration. To balance the processor load and speed up the migration process:

• Use CPU pinning.
• Optimize the processor cache.
• Ensure that there are sufficient processor resources on the source and destination servers.

5. Security and Monitoring

5.1. Security Measures

During the live migration process, it is important to take the following measures to ensure the security of the data:

• Authentication: Use SSH key-based authentication to secure communication between source and destination servers.
• Encryption: Use secure communication protocols such as TLS or VPN to encrypt data transfer.
• Access Control: Ensure that only authorized users can access the live migration process.
• Firewall: Ensure that only the necessary ports are open between the source and destination servers.

5.2. Monitoring and Logging

You can use the following methods to monitor the live migration process and detect errors:

• Log Files: Regularly check KVM, Libvirt, and QEMU log files.
• Monitoring Tools: Use monitoring tools such as Nagios, Zabbix, or Prometheus to monitor server resources (processor, memory, network, storage) and VM performance.
• Alerts: Set up a system that sends automatic alerts when anomalies or errors are detected.

6. Real-Life Examples and Case Studies

6.1. Live Migration in an E-commerce Site

A large e-commerce site uses live migration to balance the load on its servers during peak traffic periods. During peak hours, the VMs processing orders are moved to less loaded servers, ensuring the performance and accessibility of the website are maintained. In addition, when servers need to be maintained, VMs are transferred to other servers via live migration, ensuring the website continues to operate.

6.2. Live Migration in a Cloud Computing Provider

A cloud computing provider uses live migration to ensure high availability and business continuity for its customers. In the event of hardware failure, affected VMs are automatically migrated to other servers, ensuring that customers' services continue to run uninterrupted. In addition, live migration is used to dynamically adjust resources according to customer demands.

6.3. Live Migration on Database Server

A large database server uses live migration to prevent service interruptions during planned maintenance or hardware upgrades. By migrating the database server to another server via live migration, users can continue to access their data. During the live migration process, the performance and data consistency of the database server are maintained.

Tables

Table 1: Comparison of Live Migration Methods

Table 2: Factors Affecting Live Migration Performance

Visual Explanations (Textual Descriptions)

Schema 1: Live Migration Process (with Shared Storage): This schema shows the live migration process with shared storage. The memory and processor state of the VM on the source server are copied to the destination server. Since the disk data is already in the shared storage area, it is not copied. After the copying process is complete, the VM starts running on the destination server.

Graph 1: Effect of Network Bandwidth on Live Migration Time: This graph shows the effect of network bandwidth on live migration time. High bandwidth provides a shorter migration time.

Frequently Asked Questions

• Q1: Is there any downtime on the VM during live migration?
• A1: In a properly configured live migration, there may be a very short interruption (usually a few milliseconds) on the VM. This interruption is not noticeable by users.
• Q2: In which situations should I not perform live migration?
• A2: Live migration may fail in cases of network connectivity issues, storage problems, or incompatible hardware/software. Therefore, ensure the environment is suitable before performing live migration.
• Q3: How long does the live migration process take?
• A3: The live migration time depends on factors such as the size of the VM, network bandwidth, storage performance, and processor load. Generally, small VMs can be migrated in a few seconds, while large VMs can be migrated in a few minutes.
• Q4: Can data loss occur during the live migration process?
• A4: In a properly configured live migration, the risk of data loss is very low. However, data loss may occur in the event of an unexpected error (e.g., network outage). Therefore, it is recommended to back up data before performing live migration.
• Q5: Which tools can I use for the live migration process?
• A5: You can use the virsh command-line tool, the virt-manager graphical interface, or virtualization management platforms such as oVirt and OpenStack for the live migration process.

Conclusion and Summary

Live migration on KVM servers is a powerful technology that allows virtual machines to be transferred seamlessly from one physical server to another. In this article, we have discussed in detail what live migration is, why it is important, different live migration methods, how the live migration process is performed, factors affecting performance, security measures, and monitoring methods. Live migration provides significant advantages in many areas such as system maintenance, load balancing, energy saving, high availability, and testing/development. A properly configured and optimized live migration infrastructure increases the efficiency, flexibility, and reliability of data centers and cloud computing infrastructures.