a) is the above said steps is correct with the given existing and proposed setup
No. Here are some steps:
* Install Postgres on the new VM
However you get it, use the newest version you can. As of this writing, it is Postgres 17.2. Version 15 is okay, but going to 17 now means a better Postgres today, and no worrying about replacing v15 in three years.
* Create a new Postgres cluster
On the new VM, use the initdb command to create a new data directory.
Use the --data-checksums option
* Start it up
Adjust your postgresql.conf as needed
Adjust your pg_hba.conf as needed
Install any extensions used on the old VM
Start the cluster using the pg_ctl command (or systemctl)
* Test connection to the old vm from the new vm
On the new vm, see if you can connect to the old one:
psql -h oldvm -p 5432 --list
You may need to adjust firewalls and pg_hba.conf on the old vm.
* Copy the data
Run this on the new VM, adjusting ports as needed:
time pg_dumpall -h oldvm -p 5432 | psql -p 5432
Bonus points for doing this via screen/tmux to prevent interruptions
* Generate new statistics and vacuum
On the new vm, run:
psql -c 'vacuum freeze'
psql -c 'analyze'
* Test your application
* Setup all the other stuff (systemd integration, logrotate, cronjobs, etc.) as needed
As Peter mentioned earlier, this can be done without disrupting anything, and is easy to test and debug. The exact steps may vary a little, as I'm not familiar with how Amazon Linux packages Postgres, but the basics are the same.
Take it slow. Go through each of these steps one by one. If you get stuck or run into an issue, stop and solve it, reaching out to this list as necessary.
Cheers,
Greg
