When you run several servers for one service, where they physically sit matters. A Placement Group tells the platform to keep a set of servers apart from each other, or close together, when they are created. Find them under Cloud Servers, then Placement Groups.
Create a group
- Open Placement Groups and create one.
- Fill in:
- Name: for example
web-tier. - Policy: choose one:
- Anti-affinity (keep apart): servers land on different physical hosts. Use this for redundancy, so one host failing only affects one server.
- Affinity (keep together): servers land on the same host, for the lowest latency between them.
- Name: for example
- Create it.
Use it
When you launch a server, open Advanced Options in the System Config step and select the placement group. Do this for each server that should follow the policy.
For a highly available service, the common pattern is a pair of servers in an anti-affinity group behind a Load Balancer, so they never share a host and traffic moves off any server that fails.