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A placement group is a policy that controls whether Virtual Machines share the same physical server or are spread across different ones. Groups are configured and assigned to instances at creation or afterward.

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Types of groups

Three placement group types determine how Virtual Machines are distributed across physical servers.
  • Affinity groups assemble Virtual Machines on the same server, so they exchange data faster due to physical proximity.
  • Anti-affinity groups place Virtual Machines on separate physical servers. A failure on one server leaves instances on the others unaffected.
  • Soft anti-affinity groups encourage separation across servers but allow placement on the same hardware if no separate server is available. This avoids creation failures that a strict anti-affinity policy would trigger under the same conditions.

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FAQ

Placement groups have a few constraints that affect how instances are created and assigned. What happens if instances are not added to a placement group? They are placed on physical servers at random — they could end up all on the same server or spread across different ones. How many placement groups can a Virtual Machine belong to at the same time? Only one. A Virtual Machine cannot be added to two groups simultaneously.