pgismaster

What is it?

pgismaster is a very simple little program designed to indicate to a process like keepalived whether a given postgres server is a master or a standby.

This is done by checking the internal flag "pg_is_in_recovery();"; an active slave is permanently in a recovery state and a master is not.

• If run on a slave, then a message is printed to indicate that it is a slave and an exit status of 1 is returned.
• If run on a master, then a message is printed to indicate that it is a master and an exit status of 0 is returned.

This allows it to be run in the "script" parameter of keepalived to allow only a master to assert a VIP.

How do I run it?

Simply grab the compiled executable and copy it to your server. Then, call it in your script or config file.

For example, in keepalived.conf:

global_defs {
	enable_script_security
	script_user postgres    ###server is configured to allow local access here
}

vrrp_script chk_postgres {               # Requires keepalived-1.1.13
        script "/usr/local/bin/pgismaster"
        interval 10                      # check every 10 seconds
        fall 2       # require 2 failures for KO
        rise 2       # require 2 successes for OK
}

vrrp_instance VI_1 {
        interface ens192
        virtual_router_id 42
        priority 150
        state MASTER
        virtual_ipaddress {
            1.2.3.4
        }
        track_script {
            chk_postgres
        }
}

Or just run from the commandline:

$ /usr/local/bin/pgismaster
2019/10/14 16:45:31 pgismaster, Andy Gallagher 2019. See https://github.com/fredex42/pgismaster for details.
2019/10/14 16:45:31 Server is a standby
$ echo $?
1

How do I compile it?

You'll need Go 1.11 or later available to compile (but not to run). You can either head over to https://golang.org/doc/install#install or use docker (e.g. docker run --rm golang:1.12-alpine3.9)

Check out the sources: git clone https://github.com/fredex42/pgismaster

Compile it for Linux: GOOS=linux go build

Or for Windows: GOOS=windows go build

Or for Mac: GOOS=darwin go build

etc.

Dependencies are managed via go modules, so any required libraries should be automatically downloaded and compiled in the build command.

See the official Go documentation for cross-compilation options.