update_hosts_file_to_point_to_master_db

#!/bin/sh

# This script checks which node is the Primary database, and sets "db.l.lan" in /etc/hosts to it.
# We need this because our Node.js Postgres driver (npm::pg)
# doesn't support adding all the nodes IPs in the connection string

# There are two targetable databases:
#   10.0.4.40:5432  same   location pg_j
#   192.168.56.{30,31}:5432  an spiped that targets the remote pg_j 
#
# BTW, there's only a Primary + Hot-Stanby, there're no read-only replicas.
# Also, notifies syslog if there was a connection error.


db_dn="db.l.lan"
same_location=10.0.4.40
remote_location=`/bin/cat /etc/ip_inode_b`


is_primary() {
  local ip=$1
  local is_standby=`/usr/local/bin/psql postgres://$ip:5432 \
    --quiet \
    --no-align \
    --no-psqlrc \
    --tuples-only \
    --username postgres \
    --command "SELECT pg_is_in_recovery()" 2>&1`

  case "$is_standby" in
    "f")  /bin/echo 1 ;;
    "t")  /bin/echo 0 ;;
    *)    /bin/echo 0
          /usr/bin/logger "$is_standby" ;; # logs connection errors
  esac
}


update_dn_in_hosts() {
  local dbip=$1

  /bin/cat > /tmp/etc_hosts << EOF
`/usr/bin/grep -v $db_dn /etc/hosts`
$dbip $db_dn
EOF

  /bin/mv /tmp/etc_hosts /etc/hosts
}

s_is_primary=`is_primary $same_location`
r_is_primary=`is_primary $remote_location`

if [ $s_is_primary = 1 ] && [ $r_is_primary = 1 ]; then
  msg="ERROR: Split Brain. Failed to switch Primary db target"
elif [ $s_is_primary = 1 ]; then
  msg="Setting the db target to the SAME location pg instance"
  update_dn_in_hosts $same_location
elif [ $r_is_primary = 1 ]; then
  msg="Setting the db target to the REMOTE location pg instance"
  update_dn_in_hosts $remote_location
else
  msg="ERROR: Did not find any Primary database"
fi

/bin/echo "$msg"
/usr/bin/logger "$msg"


# vim: set ft=sh :