On 8/20/18 12:12 PM, Craig James wrote: > The pgbackrest documentation has a section on backing up from a standby, > but I'm having trouble figuring it out. I think it's just a terminology > problem: I can't figure out which configuration directives go on which > server. > > To begin with, I already have streaming replication running: > > Primary server (live database): "radon" > > [emolecules] > db-path=/var/lib/postgresql/9.6/main > > [global] > repo-path=/pg_archive/pgbackrest > retention-full=10 > backup-user=postgres > log-level-file=detail > > > Hot-standby server: "standby" > > [emolecules] > db-path=/var/lib/postgresql/9.6/main > recovery-option=standby_mode=on > > [global] > backup-host=radon.emolecules.com <http://radon.emolecules.com> > backup-user=postgres It's much easier just to mount the nfs volume to the standby and then you can use the same configuration on the primary and standby, though I can see below you have reasons not to do that. > The standby server is on Amazon AWS, and I want to set up a backup > Amazon S3 archive that gets its snapshot and WAL files from the standby > in order to save bandwidth costs from the primary (don't want to copy > the data twice). This is not supported. If you enable "archive_mode=always" pgBackRest will complain because there's no way to ensure that multiple server are not archiving, especially on S3. > Note that the primary is also archived to a local NFS disk. I want to > keep that going, too, but create a second archive on S3. (The reason for > this is that we're migrating from our own hardware to AWS, and during > the transition need both systems fully functional.) It's possible to backup/archive to multiple repos but the configuration is complex. I recommend that you migrate your pgBackRest repo to S3 first. That goes like: 1) Sync the pgbackrest repo to S3 (using s3fs) 2) Stop archiving by setting archive_command=false 3) Sync the pgbackrest repo again to catch any files that were missed the first time. 4) Reconfigure for S3 and enable archiving. > There are sections in the user guide on /Backup from a Standby > <https://pgbackrest.org/user-guide.html#standby-backup>/ and on /S3 > Support <https://pgbackrest.org/user-guide.html#s3-support>/, but I > can't sort out how to combine them. Apparently I need to define > pg1-host/pg1-path, and pg2-host/pg2-path, then a stanza for S3. But does > all this go in the pgbackrest.conf of the primary ("radon" in my case), > or on the standby, or somehow split across both? You have an asymmetrical configuration here since there is not backup server and shown in the pgBackRest docs. That makes configuration quite a bit harder and make failover harder. > Another question: if I modify these files, will the current standby > replica keep streaming properly? That is, can I add the S3 repository to > the current primary/standby pair without having to start over? Yes, but multiple repositories are not natively support at this time so it requires multiple configurations and some care. Regards, -- -David david@xxxxxxxxxxxxx
