If "failover_validation_command" is set, and the command returns an error,
rerun the election.
There is a pause between reruns to avoid "churn"; the length of this pause
is controlled by the configuration parameter "election_rerun_interval".
This enable selection of the method repmgrd uses to check whether the upstream
node is available. Possible values are:
- "ping" (default): uses PQping() to check server availability
- "connection": executes a query on the connection to check server
availability (similar to repmgr3.x).
The initial implementation was designed to fall back to "manual"
start/stop of repmgrd if the "repmgrd_service_..._command" parameters
were not set.
However on reflection, this is too much of a potential footgun, so
we will mandate provision of these parameters.
Basically any setting which can contain a user-defined script
*must* have the full path set, even if it's repmgr being executed.
We could potentially apply some heuristics to detect if the first
item in the setting is "repmgr" (or more precisely repmgrd's program
name), but this will require some careful thought and testing
that it works as intended.
In the sample logrotate configuration file, use "copytruncate" rather than "create",
as repmgrd currently doesn't reopen the log file (unless the configuration changes).
Per suggestion in GitHub #465.
The documentation implied it would override "promote_command", which is
not the case.
"promote_command" is used by repmgrd to execute "repmgr standby promote"
(either directly or via a custom script).
"service_promote_command" can be set to specify a package-level service
command to promote the local PostgreSQL instance from standby to primary,
e.g. Debian's pg_ctlcluster. If set, this will be executed by "repmgr standby promote".
Also update code comments to clarify usage.
Related to GitHub #473.
It's hard to imagine a use case where this isn't desirable, but
in case, for whatever reason, the user does not wish to daemonize the
process, the command line option "--daemonize=false" can be provided.
Implements GitHub #458.
