Migrating a normal Instance

Migrating a normal instance

Introduction

While Openstack provides a facility for live migrating instances between compute nodes within an availability zone (or AZ), live migration of instances between AZs is not possible. Instead, migration of an instance is performed creating a new instance in a different place that is a clone of the original.  The simple (and recommended) way to do that is to use the Nectar Dashboard to create an instance snapshot, and then launch a new instance from the snapshot.

When you migrate an instance, the static IP address (and the MAC address) for the instance will change.  A Floating IP created in one Nectar Node can technically be attached to an instance in another Node.  However, this causes operational issues, so you should avoid doing this except as a short term stop-gap measure.  (For example, it might be necessary if you have neglected to set up a DNS name for the floating IP.)  For more information on how to deal with IP address changes, see Dealing with IP addresses, DNS, Firewalls and Whitelisting Rules.

Note that there are a couple of other approaches to migrating instances that we won’t cover here:

• You could build a replacement for the instance by launching from a base image in the new AZ and then reinstalling your application software.  Important data on the old instance would then need to be transferred to the new instance.

• If the instance is a (stateless) worker in a managed cluster, you could kill the instance and use the cluster management tools to spawn a replacement.

Assumptions

The instructions on our tutorial site are based on some simplifying assumptions, as follows:

• The instance being migrated is NOT a “boot from volume” instance; see “Migrating a “boot from volume” instance”.

• The instance does NOT have an m1 or m2 flavor; see “Migrating instances with legacy flavors”.

• Your instance has no dependencies on location; e.g. access to license servers, NFS, HPC or other location-specific servers / services.  

In addition, the instructions on our tutorial site assume that storage and database migrations will be handled independently, as will dealing with any issues that arise from the IP and MAC address changes; see

• Migrating a Volume

• Migrating a Database

• Dealing with IP addresses, DNS, Firewalls and Whitelisting Rules

Quotas

This procedure needs sufficient VCPU and Instance quota to allow you to launch and run the old and new instance simultaneously.  This is for safety.  Please ask for a temporary quota increase if you need it.

To migrate a normal instance, view the tutorial here.