Hi David, > On 11. Aug, 2020, at 17:12, David Gauthier <davegauthie...@gmail.com> wrote: > > Hi: > > Our IT dept has created what they call a High Availability DB for our PG DB > (9.6.7 on linux). If the primary fails, they promise to promote the backup > to be the new primary but leave it at that. But from the perspective of the > app, I'm left with.... > 1) detecting an SQL error is a DB connectivity problem. > 2) Attempt to reconnect. If fails, try connecting to the backup server > (assume it's the new primary ?) > 3) If that works, then test to see if it is indeed a primary (try a write > statement) ? > 4) Somehow remember that the backup server is the one to connect to as the > primary for future connections. > 5) When the original primary server is fixed and brought back on-line, and > they promote it to being the new primary, then I guess my write statements > will fail because I'm still connecting to the backup. So go figure that out > and reset a pointer of sorts to the new primary ? > > Seems like a lot of work for an app and that it should be more seamless. But > maybe I'm wrong. > > I was hoping for something like a server alias that the IT team toggles as > needed between the servers so that I always know what to connect to. The > best solution would be something completely seamless... my app isn't even > aware that the primary went down, the backup was promoted, and that I'm > actually running on a different server. Is something like that possible ? > > Thanks for any replies !
If you're a developer, you can take a look at: https://www.postgresql.org/docs/current/libpq.html If your application uses libpq, then you can have it connect to the primary database, no matter on what host the primary and the replica currently is. Look at: https://jdbc.postgresql.org/documentation/head/connect.html You can especially do something like: jdbc:postgresql://host-a:5432,host-b:5433/postgres?targetServerType=master You can always download the current driver from: https://jdbc.postgresql.org Does that help? Cheers, Paul
