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
The topology planner writes a sketch: one primary takes writes, and each other node receives the log. You name how many sites must be able to stand alone. It does not open replication. The lag interpreter reads seconds and bytes you type. Thirty seconds is long enough to look at a large transaction, a slow apply, or a network pause. A large byte queue points at replica disk and apply rate. Small numbers mean you keep watching.
Do not start replication during the reading. Do not send a log to a host you do not run. Do not fail over.
192.0.2.10, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. example.com is a documentation name. A sample password is replaced. It is not a password you keep.
The change you can finish
Apply nothing while you are writing the note. When the lab window opens, it is one change on the database named in the ticket. Read the draft, then the database, then decide.
Rollback is the backup, the file, or the snapshot you saved first. You do not invent a rollback after the only copy is gone.
- Type nodes and sites.
- Read the sketch.
- Type lag only if you already measured it.
- Do not start replication.
- Stop.
Mistakes that outlive the statement
Replication Explained goes wrong in a small set of ways. The list is here so the ticket can forbid them before the window.
- Replication started during the reading.
- A replica you do not run.
- A failover started from the sketch.
- A password in the note.
Decisions to write down
One decision for Replication Explained: Both hosts are yours. The sketch was read. Nothing was started. And no password is in the note.
Checks before you call it done
Confirm this before you call the change done: The primary is written. The replicas are written. Nothing was started. No password is in the note. And you administer both sides. If one of those fails, stop.
Before you leave the database
Replication Explained ends when the database in the prompt is the database in the ticket. If it is not, you are on the wrong database. Stop.
The draft stays a draft until a person has read the names in it. A generator does not log into the database. You delete a line that names a host, a database, or an account you did not write down.
192.0.2.10, 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 database 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. A sample password in a draft is replaced. It is not a password you keep.
One change is the window. If two things move and the result is wrong, you will not know which one did it.
If the same step fails twice, stop for the day. Restore the copy you took first.
A second person reads the database name and the change aloud. If they cannot find them in the ticket, the note is not done.
This page is a planning guide. It is not a vendor manual, not an official standard, and not permission to touch a database you do not administer. You do not disable authentication, a firewall, or TLS 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.