Basic CH-Remote Live Migration Test Guide

by Alex Johnson 42 views

This guide outlines how to set up a very basic live migration test using ch-remote. While this might not directly belong to libvirt-tests, the CHV upstream integration test infrastructure has limitations. Therefore, having a stripped-down live migration test based on ch-remote in our pipeline is valuable.

Why CH-Remote Live Migration Testing Matters

In the realm of virtualization, live migration stands as a critical feature. Live migration enables the seamless transfer of a running virtual machine (VM) between different physical hosts without any noticeable downtime. This capability is essential for various scenarios, including:

  • Maintenance: Live migration allows administrators to perform maintenance tasks on physical servers without interrupting the services running on the VMs.
  • Resource Optimization: VMs can be moved to hosts with more available resources to improve performance and balance workloads.
  • High Availability: In case of hardware failures, VMs can be migrated to healthy hosts to ensure continuous operation.

Given the importance of live migration, robust testing is paramount. This guide focuses on creating a basic ch-remote live migration test. While a full-fledged integration test suite might be ideal, practical considerations often necessitate a more streamlined approach. The method described here provides a foundational level of testing, ensuring that the core live migration functionality operates as expected.

This approach is particularly useful when direct integration with tools like libvirt-tests is not feasible or practical. By focusing on a basic ch-remote setup, we can isolate the live migration process and verify its functionality without the complexities of a larger testing framework. This allows for quicker iteration and easier troubleshooting, ensuring that the fundamental aspects of live migration are sound. Furthermore, this stripped-down test can serve as a building block for more comprehensive tests in the future, providing a solid base upon which to expand testing efforts.

Prerequisites

Before diving into the commands, let's ensure you have the necessary components:

  • Cloud Hypervisor (CHV): This is the virtualization platform we'll be using.
  • ch-remote: A command-line tool for interacting with Cloud Hypervisor.
  • Linux Kernel: A suitable kernel image (e.g., linux_6_12.bzImage).
  • Initramfs: An initial RAM file system image.
  • Cargo: Rust's package manager and build tool.

These components are crucial for setting up the test environment and executing the live migration. Cloud Hypervisor acts as the hypervisor managing the virtual machines, while ch-remote provides the interface for sending migration commands. A Linux kernel and initramfs are required to boot the virtual machine within CHV. Cargo, being the Rust build tool, is necessary to compile and run both Cloud Hypervisor and ch-remote.

Ensuring that these prerequisites are in place and correctly configured is the first step towards a successful live migration test. Each component plays a specific role, and any misconfiguration can lead to failures or unexpected behavior during the migration process. Therefore, it's essential to verify that all dependencies are satisfied before proceeding with the test setup. This proactive approach helps in identifying and resolving potential issues early on, making the testing process smoother and more reliable.

Setting Up the Test Environment

We'll need two instances of Cloud Hypervisor (CHV 1 and CHV 2) to simulate the migration source and destination. Here are the commands to launch them:

CHV 1 (Source)

reset; rm -f /tmp/chv1.sock && cargo run --release --bin cloud-hypervisor -- --api-socket /tmp/chv1.sock --kernel ./linux_6_12.bzImage --cmdline "console=ttyS0" --serial tty --console off --initramfs ./initrd --seccomp log -vv --memory size=8G --cpus boot=8

Let's break down this command:

  • reset: Clears the terminal.
  • rm -f /tmp/chv1.sock: Removes any existing socket file.
  • cargo run --release --bin cloud-hypervisor: Runs the Cloud Hypervisor binary in release mode.
  • --api-socket /tmp/chv1.sock: Specifies the API socket for communication.
  • --kernel ./linux_6_12.bzImage: Indicates the kernel image to use.
  • --cmdline "console=ttyS0": Sets the kernel command line.
  • --serial tty: Enables serial console output.
  • --console off: Disables the graphical console.
  • --initramfs ./initrd: Specifies the initramfs image.
  • --seccomp log: Enables seccomp logging.
  • -vv: Enables verbose logging.
  • --memory size=8G: Allocates 8GB of memory to the VM.
  • --cpus boot=8: Assigns 8 virtual CPUs to the VM.

CHV 2 (Destination)

reset; rm -f /tmp/chv2.sock; cargo run --release --bin cloud-hypervisor -- --api-socket=/tmp/chv2.sock

This command is similar to the one for CHV 1, but it doesn't include the kernel, initramfs, and other VM-specific parameters. This is because CHV 2 will receive the VM's state during the live migration.

These two instances of Cloud Hypervisor form the foundation of our live migration test environment. CHV 1 hosts the virtual machine that will be migrated, while CHV 2 acts as the destination to which the VM will be moved. The configuration of CHV 1 includes all the necessary parameters to boot a VM, such as the kernel image, initramfs, memory allocation, and CPU assignment. CHV 2, on the other hand, is set up to listen for incoming migration data, requiring only the API socket to be configured. This separation of roles allows for a clear and controlled live migration process, making it easier to verify the functionality and troubleshoot any issues that may arise.

Initiating and Receiving the Migration

With the CHV instances running, we can now initiate the live migration using ch-remote.

Sending the Migration (CHV 1)

cargo run --bin ch-remote -- --api-socket=/tmp/chv1.sock send-migration tcp:127.0.0.1:1337 --downtime 200 --migration-timeout 12000
  • cargo run --bin ch-remote: Runs the ch-remote binary.
  • --api-socket=/tmp/chv1.sock: Specifies the API socket of the source CHV instance.
  • send-migration tcp:127.0.0.1:1337: Initiates the migration over TCP to the specified address and port.
  • --downtime 200: Sets the maximum acceptable downtime in milliseconds.
  • --migration-timeout 12000: Sets the migration timeout in milliseconds.

This command instructs ch-remote to send the VM's state from CHV 1 to CHV 2. The --downtime parameter is crucial, as it defines the maximum interruption time that the VM can experience during the migration. A lower downtime value is generally desirable to minimize service disruption. The --migration-timeout parameter sets a limit on the total time allowed for the migration process to complete, preventing the migration from hanging indefinitely in case of issues.

Receiving the Migration (CHV 2)

cargo run --bin ch-remote -- --api-socket /tmp/chv2.sock receive-migration tcp:127.0.0.1:1337
  • cargo run --bin ch-remote: Runs the ch-remote binary.
  • --api-socket /tmp/chv2.sock: Specifies the API socket of the destination CHV instance.
  • receive-migration tcp:127.0.0.1:1337: Listens for incoming migration data on the specified address and port.

This command tells ch-remote to listen for incoming migration data on the specified TCP port. CHV 2 will receive the VM's memory, CPU state, and other relevant data, effectively taking over the VM's execution. The successful completion of this command indicates that the live migration has been initiated and the destination CHV instance is ready to receive the migrating VM.

Expected Outcome

If everything is configured correctly, the VM running on CHV 1 should seamlessly migrate to CHV 2. You should observe the following:

  • The VM on CHV 1 will pause briefly.
  • Data transfer will occur between CHV 1 and CHV 2.
  • The VM will resume execution on CHV 2.

This process demonstrates a basic live migration, ensuring that the core functionality is working. The brief pause during migration is the downtime, which should ideally be kept as low as possible. The data transfer phase involves the transmission of the VM's memory and state from the source to the destination, allowing the VM to continue its execution on the new host. Observing the VM successfully resuming on CHV 2 confirms that the live migration has been completed successfully.

Troubleshooting

If the migration fails, here are some common issues to check:

  • Socket Conflicts: Ensure that the API sockets (/tmp/chv1.sock and /tmp/chv2.sock) are not in use by other processes.
  • Network Connectivity: Verify that CHV 1 and CHV 2 can communicate over the network (in this case, 127.0.0.1:1337).
  • Firewall: Check if any firewall rules are blocking the TCP connection.
  • Resource Constraints: Ensure that CHV 2 has sufficient resources (memory, CPU) to accommodate the migrated VM.

These troubleshooting steps cover the most common causes of live migration failures. Socket conflicts can arise if another process is already using the specified API socket, preventing CHV or ch-remote from binding to it. Network connectivity is crucial, as the source and destination hosts must be able to communicate to transfer the VM's state. Firewalls can interfere with this communication by blocking the necessary TCP connections. Finally, resource constraints on the destination host can prevent the successful migration of the VM, as it may not have enough memory or CPU to run the migrated instance.

Conclusion

This guide provides a basic framework for testing ch-remote live migration. While it's a stripped-down version, it serves as a valuable starting point for ensuring the functionality of live migration in your environment. Further testing and integration with more comprehensive test suites can build upon this foundation.

For more in-depth information on virtualization and live migration, visit the libvirt website.