Before you perform a system migration, you need to assess your service contents, the time required for migration, and related costs, and create a migration plan accordingly. This topic describes the key assessment factors that you need to consider when planning a system migration.
Operating system requirements
- Kernel version: CentOS/Red Hat 5 or later, Ubuntu 10 or later, and Windows Server 2003 or later. If your kernel version is earlier than the preceding versions listed, you need to upgrade your kernel to a supported version.
- Virtualized driver: The KVM virtio driver must be installed.
- Service software: For Linux systems, rsync is required and curl is recommended. For Windows systems, the Volume Shadow Services (VSSs) must be operating properly.
- Grand Unified Bootloader (GRUB): For operating systems with earlier kernel versions, such as CentOS/Red Hat 5 and Debian 7, GRUB must be upgraded to V1.99 or later.
- Disk size: The system disk must be 40 to 500 GiB, and the data disk must be 20 to 32768 GiB.
- Service suspension: If you are running large service applications, such as Oracle, SQLServer, MongoDB, MySQL, and Docker databases, we recommend that you suspend them before performing the service migration. If such service applications cannot be suspended, we recommend that you exclude the corresponding data directories from being migrated, and then synchronize the database data after the server migration is completed.
- Large data volume: If there are a massive number of data files, we recommend that you migrate only the server application environment, and then decide whether to migrate these data files by using a physical connection or Lightning Cube for faster transfer.
- Software licensing: You need to assess whether the software that must be licensed in the source system requires a new license after migration.
- Network configuration: The Internet IP address changes after migration. You need to assess whether this will affect the original services.
Network transfer modes
You need to assess the network transfer mode required for the server system to be migrated.
Server migration is divided into three phases:
- Migration resource preparation
- Data transfer
- Migration closing
All three phases are conducted through the Internet. Therefore, the server to be migrated must have access to the following Alibaba Cloud service addresses and ports:
- Phase 1 and phase 3
- ECS service: https://ecs.aliyuncs.com, port 443. For more addresses, see Request structure.
- VPC sevice: https://vpc.aliyuncs.com, port 443.
- STS service: https://sts.aliyuncs.com, port 443.
- Phase 2: IP address (the Internet address by default) of the temporary intermediate instance, port 8080 and port 8703.
If the preceding migration method cannot be conducted through the Internet entirely, the Alibaba Cloud migration service supports the following transfer modes for specific network environments:
- Default Internet transfer: The Internet is used by default in phases 1, 2, and 3.
- Manual intranet transfer: The Internet is used in phases 1 and 3 and the VPC is used in phase 2. Manual intranet transfer applies to the server systems that can access the VPC but cannot access the preceding Alibaba Cloud service addresses. In this case, you need to prepare an additional system of the same type that can access the preceding Alibaba Cloud service addresses to cooperate with the operation. For more information, see VPC-based migration.
- Automatic intranet transfer: The Internet is used in phases 1 and 3. The VPC is used in phase 2. Automatic intranet transfer applies to the server systems that can access the preceding Alibaba Cloud service addresses and the specified VPC. This mode also applies to the server systems whose data is transferred through the VPC in phase 2. Compared with Manual intranet transfer, this mode is simpler. For more information, see VPC-based migration.
The following information is recommended if you want to migrate your servers in batches.
Before a batch migration, you need to:
- Contact your local network operator to confirm the traffic limits, or set the upper limit of the transmission bandwidth by using the Cloud Migration tool.
- Open a ticket to cancel the limits on the number of Alibaba Cloud images and the quota of Pay-As-You-Go resources (for example, vCPU).
During a batch migration, you need to:
- Check whether the server system supports automated batch O&M to run commands in batches and run the Cloud Migration tool.
- Check whether you need to analyze the statistics of batch migration progress logs.
After a batch migration, you need to:
- Create and configure the server systems.
- Validate the server systems.
The migration period is determined by the number of servers and the actual data volume. We recommend that you assess how much migration time is required by conducting tests in advance.
The migration period is divided into three parts: pre-migration, migration, and post-migration.
Pre-migration time = migration preparation time
The migration preparation time varies with the actual conditions.
Migration time = data transfer time + image production time (optional)
Data transfer time = actual data volume / actual transfer rate
Image production time = actual data volume / snapshot service speedNote By default, the Cloud Migration tool enables the compression transfer function during data transfer. This results in an transfer rate increase by 30% to 40%. The image production time depends on the snapshot service of Alibaba Cloud (the current speed is approximately 10 to 30 MB/s).
Post-migration time = incremental system synchronization time after migration (optional) + system configuration validation time
Incremental system synchronization time = actual incremental data volume / actual transfer rate
The system configuration validation time varies according to actual conditions.
The Cloud Migration tool is provided free of charge. However, an ECS instance named INSTANCE_FOR_GOTOALIYUN is created by default under your Alibaba Cloud account during the migration to act as an intermediate station. The ECS instance is a Pay-As-You-Go instance. You need to ensure that the credit card associated with your account has a sufficient balance.