Change MongoDB default port

change_mongodb_port.sh

#!/bin/bash

echo 'DISABLE PUPPET ON ALL MONGO MACHINES AT FIRST'

old_port=27017
new_port=27018

# This script change default port of mongod instance and keep old port
# redirected to a new port

puppet agent --disable 'kayn: changing default mongod port'
echo 1 > /proc/sys/net/ipv4/ip_forward
iptables -t nat -I PREROUTING -p tcp --dport $old_port -j REDIRECT --to-port $new_port

# previous redirect logs a lot of stuff!
mv /etc/rsyslog.d/iptables.conf /tmp/
systemctl restart rsyslog

sed -i "s/$old_port/$new_port/" /etc/mongod.conf
systemctl restart mongod

echo 'Now open mongo shell on primary and change the port by in following steps (if you are on primary, you need to stepDown before by `rs.stepDown()`:

# load configuration

cfg = rs.conf()

# use proper ID instead of X and check if the name matchs with the member you are changing a port

cfg.members[X].host

# change port by

cfg.members[X].host = "mongo0X:27018"

# reload configuration

rs.reconfig(cfg)

# now check the replicaSet status and wait until changed member is synced (journal on arbiter can start to grow rapidly, please watch the size by `watch -n60 du -sh /var/lib/mongodb/journal`. If it will grow, you need to stop mongo, remove everything in /var/lib/mongodb/ and start arbiter again). 

rs.status()'


echo "Once the mongos routers and replica sets are reconfigured properly in puppet, remove the redirect firewall rules by:

iptables -t nat -D PREROUTING -p tcp --dport $old_port -j REDIRECT --to-port $new_port
echo 0 > /proc/sys/net/ipv4/ip_forward

and enable puppet"