About placement groups
What it is. Placement groups are a setting that determines whether virtual machines will be hosted on the same physical server or on different ones.
Types of groups. There are affinity and anti-affinity ones. An affinity group assembles equipment on one hypervisor — the machines included in it will be launched on the same physical server. Anti-affinity works the opposite way: all machines in this group will be launched on different physical servers.
What it is used for. Each group has its own advantages. Machines launched in one affinity group will exchange data faster, because they are located on the same server. Anti-affinity group increases fault tolerance of a cluster: even if something happens to one server, machines on the other will remain available.
What happens if you don't add instances to a placement group. They will be placed on physical servers randomly — may get on the same one or on different ones.
How many placement groups a machine can belong to at the same time. Only to one group — it is impossible to add it to two groups at once, even if these groups are of different types (affinity and anti-affinity).
Instructions for working with placement groups in our system are presented below.
How to create a group
In the “Placement Groups” section, create a new group. Give it a name and select a policy — affinity or anti-affinity — and click Create Placement Group.
How to create an instance included in a placement group
When creating an instance, in the "Additional options" section, move the "Add to placement group" slider and select a group or create a new one — the machine will be a member of it.
How to add a previously created instance to a group
In the instance menu, open the “Placement Group” tab. Select the previously created group where you want to add the instance to, or create a new one. Click “Add”.
How to move an instance from one group to another
In the instance menu, open the “Placement Group” tab. Remove a machine from one group and add it to another —you can add it to a new one or to a previously created one.