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Overview

An instance group is a name you attach to a set of instances so they can be listed and reasoned about together. It is purely organisational: grouping instances does not affect where they are placed, how they are networked, or how they scale.
There is no console screen for instance groups. The four endpoints below exist and work, but nothing in the interface creates, lists or assigns them. This is an API-only feature today.If you want to organise instances from the console, use tags instead — the machine list can group by tag, which is the same job done in a place you can actually see.

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What it is not

Three other features have similar names and do different things. This is the one that catches people out.
If you are reaching for “instance group” because you want instances spread across hosts for resilience, you want an affinity group. If you want the count to change with load, you want an autoscaling group.

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The API

name is the only field, and it is required on both create and rename.
Group membership is set when an instance is deployed, through the create call — not by an endpoint on the group itself. There is no “add instance to group” operation.

Affinity Groups

Placement rules, which is usually what people want.

Lists and filters

Tag grouping — the console-visible alternative.

Autoscaling Groups

Changing instance count automatically.

Virtual Machines

Where membership is assigned.