Compute Categories and Compute Tags can be used to specify which application instances can run on a specific compute node. An instance can be migrated from one compute node to another by modifying the instance's compute category or tags. Migrating an instance from one compute node to another involves zero downtime, continuous service availability, and complete transaction integrity. The Ignite VNC console to an instance uses a URL that includes the compute node's IP address; when an instance migrates to a new compute node, the VNC console will automatically close since the URL is no longer valid, and reopening it will open a URL including the new compute node's IP address.
Each compute node must belong to exactly one compute category. A compute node's category can be changed only if no application instances are running on it.
In the Compute Restrains portion of an application instance's profile, the instance can be configured to run on compute nodes in Any category, or only on compute nodes in a specific category.
An instance's compute category can be changed while the instance is running. If the instance is running on a compute node in category Category1 and the instance's category is changed to Category2, the instance will automatically migrate to a compute node in Category2. In the Ignite Management Portal, the instance will appear to shut down, then start on the other compute node; but the instance will actually remain running throughout the migration.
Compute resources are allocated to virtual datacenters by category. When you create or edit allocations for a virtual datacenter, you enter the amount of CPU and memory to allocate from each category, rather than from individual compute nodes.
Unlike with categories, compute nodes and application instances can have any number of compute tags.
An instance can run on any compute node that has at least the same tags as the instance. That is, if an instance has tags Tag1 and Tag2, it can run on any compute node that also has tags Tag1 and Tag2, regardless of any additional tags that compute node has. However, that instance cannot run on a compute node that has Tag1 but not Tag2 or vice versa.
Compute tags can be added to or removed from a compute node while instances are running on the node. When removing compute tags, you will be asked to select an action plan for affected instances:
- Migrate: Ignite will attempt to migrate the instance to another compute node that meets its compute requirements.
- Relax profile: Ignite will remove the tag requirements from the instance's compute profile.
- Shut down: Ignite will shut down the instance.
- Force shut down: Ignite with force shut down the instance.
Compute tags can be added to or removed from an application instance while it is running. If the instance is running on a compute node that lacks the new tag, the instance will be automatically migrated to a compute node that has the required tags. In the Ignite Management Portal, the instance will appear to shut down, then start on the other compute node; but the instance will actually remain running throughout the migration.