Elastic Compute Service:Migrate the operating system of an ECS instance

Supported source operating systems and destination operating systems

Usage notes

• During the migration process, the following operations are performed on the ECS instance: creating snapshots for basic disks, reinstalling software packages, creating a custom image from a system disk snapshot, replacing the system disk, stopping the ECS instance, and starting the ECS instance. After the system disk is replaced, a disk is created as the new system disk. Automatic snapshots that are released along with the original disk are deleted and cannot be restored. We recommend that you back up important data and plan a proper migration time to prevent the preceding operations from affecting your business.
• During the migration process, do not stop, restart, or release the ECS instance in manual mode or by using O&M scripts.
• During the migration process, snapshots are created for all disks to back up data. You are charged for snapshots based on the pay-as-you-go billing method. For more information, see Snapshots.
• The migration of an operating system is irreversible. You need to reinstall software packages during the migration process. Before you migrate the operating system of your ECS instance, we recommend that you create snapshots for the ECS instance to back up data. For more information about snapshots, see Snapshot overview.
• YUM or DNF is used for migration. Make sure that these two components run as expected.

Limits

• Anolis OS and Alibaba Cloud Linux do not provide i686-based software packages. If your CentOS operating system comes with i686-based software, you cannot migrate your operating system to Anolis OS or Alibaba Cloud Linux.
• To migrate from CentOS 7 to Alibaba Cloud Linux 2, take note of the following limits:
  • Alibaba Cloud Linux 2 uses kernel version 4.19, which is incompatible with kernel version 3.10 of CentOS 7. Applications that must call the kernel API to program, such as to build out-of-tree kernel modules and to enable hardware, must be assessed beforehand to determine whether a direct migration is feasible and ensure that the applications can run normally after the migration.
  • Alibaba Cloud Linux 2 does not support GUIs. As a result, the migration tool cannot be used to migrate away from CentOS 7 operating systems (OSs) that are configured with a GUI.
• To migrate from CentOS 8 to Alibaba Cloud Linux 3, take note of the following limits:
  Alibaba Cloud Linux 3 uses Linux Kernel 5.10 LTS, and its GNU toolchain contains GCC 10.2, Binutils 2.35, and glibc 2.32. CentOS 8 software is compatible with Alibaba Cloud Linux 3. When you use the migration tool to migrate from CentOS 8 to Alibaba Cloud Linux 3, the migration tool determines which features and software may be limited after the migration. The following table describes the limits.

  Feature or software	Supported	Migration affected	Description
  GUI	No.	Yes.	Alibaba Cloud Linux 3 does not support GUIs. As a result, if your CentOS 8 operating system is configured with a GUI, you cannot use the migration tool to migrate to Alibaba Cloud Linux 3.
  i386-based software packages	No.	Yes.	Alibaba Cloud Linux 3 does not provide i386-based software packages. If your CentOS 8 operating system comes with i386-based software packages, you cannot use the migration tool to migrate to Alibaba Cloud Linux 3. To prevent system exceptions, you must delete the i386-based software packages before you perform a migration.
  epel-modular	No.	No.	The Extra Packages for Enterprise Linux (EPEL) repositories of CentOS 8 and Alibaba Cloud Linux 3 depend on different platforms. You can migrate from CentOS 8 to Alibaba Cloud Linux 3, but you cannot install the software packages that are based on epel-modular after the migration.
  Compatibility with C/C++ programs	Not guaranteed.	No.	Alibaba Cloud Linux 3 comes with software packages that are optimized for better compatibility with C/C++ programs. The GNU toolchain of Alibaba Cloud Linux 3 contains GCC 10.2, Binutils 2.35, and glibc 2.32. After you migrate from CentOS 8 to Alibaba Cloud Linux 3, we recommend that you compile and verify your C/C++ programs by using the new GNU toolchain to prevent incompatibility.
  Kernel module compatibility	No.	No.	Alibaba Cloud Linux 3 uses Linux Kernel 5.10 LTS. Alibaba Cloud Linux 3 is compatible with CentOS 8 software but is not fully compatible with kernel version 4.18 in CentOS 8. If your business uses the applications that depend on APIs, such as building out-of-tree kernel modules and using hardware resources, you must assess these applications beforehand. This way, you can determine whether a direct migration is feasible and make sure that the applications can run normally after the migration.
  MySQL database	Only migrations to the same or later MySQL versions are supported.	No if the MySQL version provided by Alibaba Cloud Linux 3 is the same as or later than that provided by CentOS 8 Yes if the MySQL version provided by Alibaba Cloud Linux 3 is earlier than that provided by CentOS 8	Alibaba Cloud Linux 3 supports MySQL. However, MySQL version downgrades are not supported. If the MySQL version provided by Alibaba Cloud Linux 3 is earlier than that provided by CentOS 8, you cannot use the migration tool to migrate from CentOS 8 to Alibaba Cloud Linux.
  Operating system hot migration	No.	No.	During the migration procedures, software packages are re-installed. This causes services to restart and results in brief service interruptions. To prevent impacts on services, we recommend that you back up data and isolate the source operating system environment before you use the migration tool to migrate from CentOS 8 to Alibaba Cloud Linux 3. For information about how to back up data, see Snapshot overview.

  The migration tool consumes resources to download and install software packages during migration. Before you perform a migration on an Elastic Compute Service (ECS) instance, make sure that the following resources are available:

  • Amount of memory space: 300 MiB
  • Amounts of disk space available for the following directories:
    • /usr: 250 MiB
    • /var: 1.5 GiB
    • /boot: 50 MiB

  Note If your instance has a smaller number of vCPUs, little memory, and a small amount of storage space (system disk space and data disk space), we recommend that you stop services that are running on the instance before you migrate the instance to Alibaba Cloud Linux 3. This way, you can prevent migration failures caused by insufficient resources.

Procedure

1. Log on to the ECS console.
2. In the top navigation bar, select the region where the ECS instance that you want to migrate resides.
3. Find the ECS instance and choose More > Disk and Image > Replace Operating System in the Actions column.
4. In the Replace Operating System dialog box, select Migrate Operating System.
5. Read the precautions, select I acknowledge and accept these risks and authorize Alibaba Cloud to create snapshots for all disks on the instance, and then click Continue to Replace Operating System.
6. In the Replacement Operating System section of the Migrate Operating System dialog box, select the operating system to which you want to migrate the ECS instance.
7. Clear If an error occurs during the migration process, the operating system replacement operation is automatically canceled or leave this option selected.
   • If this option is selected, the operating system migration operation is automatically canceled when an error occurs during the migration process. The ECS instance remains in the Stopped state. You can migrate the operating system of the instance again.
   • If this option is cleared, OS Replacement Error appears in the Status column of the instance when an error occurs during the migration process. You can move the pointer over OS Replacement Error and click Cancel Operating System Replacement to cancel the operating system migration operation. Then, you can migrate the operating system of the instance again.
8. Click Confirm.
   Approximately 10 minutes are required to migrate the operating system. This excludes the period of time that is required to create snapshots. On the Instances page or the Instance Details page, you can view the progress of the migration task.

   • If the operating system is migrated, the state of the instance changes from Replacing OS to Running.
     Note When the operating system is being migrated, you can move the pointer over Replacing OS to view the progress of the migration task.
   • If the operating system fails to be migrated, the instance enters the OS Replacement Error state. You can move the pointer over OS Replacement Error to view the cause of the error. Troubleshoot the error and then migrate the operating system of the instance again.