Application Layer Migration

Server migration

Server migration is a common type of rehosting. While servers can run many applications like Nginx, databases, containers, middleware, and big data tools, some applications focus on data. For these, we often use separate data migration instead of server migration. Server migration moves both the applications and the OS. There are three types of server migration:

**Table 1** Server migration methods
Server	Method	Scenario	Remarks
VM/PM	Redeployment	The customer does not need to keep the OS and can accept long downtime.	-
	Migration using SMS (free of charge)	The customer wants to keep the OS but can accept only a short downtime.	Recommended. Huawei Cloud offers the technical support.
	Image import and export	The customer wants to keep the OS and can accept long downtime.	-

Redeployment: For public cloud migration, use the CI/CD pipeline to automate and redeploy your applications.
Migration using SMS: SMS helps you move applications and data from on-premises x86 servers or VMs on other clouds to Huawei Cloud's ECSs.
Figure 1 Process of migration using SMS

The Agent on the source server gets the migration instruction from SMS, then creates a security certificate and key. It sends these to the target server using Huawei Cloud OpenStack metadata management. Both servers then restart and use the new certificate to set up a secure SSL channel. Services stay up during migration, with just a brief pause needed before starting the target ECS in Continuous Synchronization mode. SMS keeps downtime to a minimum. For details about SMS, see the Server Migration Service Documentation.
Image import and export: Server migration can use Huawei Cloud's Image Management Service (IMS) to create private images from existing ECSs or external image files. You can also import existing service cloud images to the cloud platform. This helps with moving services to the cloud and deploying them in batches.
Figure 2 Image import and export solution

If SMS cannot move your whole system over the network, use IMS instead. Make private images from the source server's system and data disks, then upload these images to Huawei Cloud OBS. In IMS, create private images from the uploaded files and use them to set up ECSs. After migration, the host OS, system settings, and data files will match those on the source server. For details, see the Image Management Service Documentation.

Container migration
A container is a lightweight high-performance resource isolation mechanism implemented based on the Linux kernel. It is a built-in capability of the OS kernel. Kubernetes is an open-source system for automating deployment, scaling, and management of containerized applications. For developers, Kubernetes is a cluster operating system. Kubernetes provides functions such as service discovery, scaling, load balancing, self-healing, and even leader election, freeing developers from infrastructure-related configurations.

Cloud Container Engine (CCE) is a highly scalable, high-performance, enterprise-class Kubernetes service to run Docker containers. With CCE, you can easily deploy, manage, and scale containerized applications on Huawei Cloud. CCE is an enterprise-grade container service built on open-source Kubernetes. It helps businesses manage containerized apps with high performance and reliability. CCE supports native Kubernetes apps and tools, making it easy to set up a container runtime in the cloud.

You can access CCE, a hosted Kubernetes service, using the CCE console, kubectl, or Kubernetes APIs. For details, see the Cloud Container Engine Documentation.

This section uses migrating containerized applications from other clouds to CCE as an example. The following figure shows the details.

Figure 3 Container migration

The container image migration procedure is as follows:
1. Export the container images used by the third-party cluster.
2. Pull the images to the client machine by following the instructions provided in the third-party container image service.
3. Upload the image files to Huawei Cloud SoftWare Repository for Container (SWR).
4. Run the docker pull command to upload the image to Huawei Cloud. For details, see the SoftWare Repository for Container Documentation.