Don't allow members outside primary region to become primary

[DAlperin]

Towards https://github.com/superfly/postgres-on-machines/issues/4

[davissp14]

Nice! We may actually want to configure priority on members outside of the primary region as well.
https://raw.githubusercontent.com/2ndQuadrant/repmgr/master/repmgr.conf.sample

[DAlperin]

@davissp14 if we just don't want nodes outside the primary location to be promoted isn't that already accomplished just with location?

In a failover situation, repmgrd will check if any servers in the same location as the current primary node are visible. If not, repmgrd will assume a network interruption and not promote any node in any other location (it will however enter degraded monitoring mode until a primary becomes visible).

[davissp14]

I'd have to confirm by reading the source, but my interpretation is that Location is primarily used for mitigating network splits. E.G. If all nodes are visible within the location out-of-region nodes in a different location would still be eligible based on their priority setting.

[DAlperin]

Ah interesting. My impression from the docs was that location dictates whether a node can be promoted. A quick grep in the source yields this but I'll read a bit more https://github.com/EnterpriseDB/repmgr/blob/master/repmgrd-physical.c#L3022-L3027

[DAlperin]

If I'm reading this right (which I'm not 100% sure I am) I think nodes outside the primary location will not be a candidate for election: https://github.com/EnterpriseDB/repmgr/blob/master/repmgrd-physical.c#L4372-L4402

[davissp14]

https://github.com/EnterpriseDB/repmgr/blob/master/repmgrd-physical.c#L4715-L4729

As far as I can tell, using location alone should do the trick!

Feel free to merge whenever!

[DAlperin]

Closed https://github.com/superfly/postgres-on-machines/issues/4