This is an original planning guide. It is not a vendor manual, an official standard, or legal advice. Example addresses use documentation ranges. Review every command before you paste it.
What this hour is for
N+1 means the cluster still runs the guests if one host is gone. The calculator uses counts you type. Thin and thick are choices about when disk space is reserved. Neither tool connects to a cluster.
Write what you will drop if two hosts fail, because N+1 does not cover that. Do not fail a production host over during the reading. Do not treat thin provisioning as free space you have already bought.
One cluster you administer.
The change you can finish
Apply nothing while you are writing the note. When the lab window opens, it is one change on the host named in the ticket. Read the draft, then the host, then decide.
Rollback is the file, the package version, or the snapshot you saved first. You do not invent a rollback after the only copy is gone.
- Name the cluster.
- Type host count, guest need, and disk.
- Read whether one host can disappear.
- Mark thin space as not yet bought.
- Do not fail a host over.
- Stop.
Mistakes that outlive the command
Cluster Capacity and N+1 Planning goes wrong in a small set of ways. The list is here so the ticket can forbid them before the window.
- A production failover during the reading.
- Thin space treated as purchased.
- A cluster you do not administer.
- N+1 assumed to survive two failures.
Decisions to write down
One decision for Cluster Capacity and N+1 Planning: The cluster is yours. One-host loss is the question. Thin is labeled. No failover was started. And the tools did not connect.
Checks before you call it done
Confirm this before you call the change done: Host count is written. The one-host result is written. Disk is labeled thin or thick. No failover was started. And the cluster is yours. If one of those fails, stop.
# N+1 is one host, not two.
# Thin space is not space you have bought.
# Do not fail over production from this page.Before you leave the host
Cluster Capacity and N+1 Planning ends when the hostname in the prompt matches the hostname in the ticket. If it does not, you are on the wrong host. Stop. A command that succeeded on the wrong host is not progress.
The draft stays a draft until a person has read the names in it. A generator does not log into the host and does not know which disk is empty. You delete a line that names a host, a path, or an account you did not write down.
192.0.2.10/24, gateway 192.0.2.1, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. example.com is a documentation name. They belong in the note. They are not values you leave on a host because a draft included them.
prompt-for-this is a reminder that a secret is missing. It is not a password, a key, or a token you save in the ticket or in git. The real secret stays in the password store.
One change is the window. If two things move and the result is wrong, you will not know which one did it. The next change waits for its own page.
If the same step fails twice, stop for the day. The failure is the result. Adding a forum command beside a half-applied change produces a host nobody can rebuild. Restore the copy you took first.
A second person reads the hostname and the change aloud. If they cannot find them in the ticket, the note is not done. Silence is not agreement. Then leave the host alone.
This page is a planning guide. It is not a vendor manual, not an official standard, and not permission to touch a host you do not administer. You do not disable a firewall, AppArmor, or SELinux to make a check pass.
Tools for this guide
These tools run in the browser on this site. They do not log into your machines.
Related pillar guides
More in this cluster
The pillar for this page, and the next published pages filed with it.