Running a custom startup script in CentOS / RHEL 7

Hi All,

During my work at Adroitlogic, in one of my tasks I had to start & configure a set of EC2 machines which included our B2B AS2 integration solution AS2Station. This was a recurring task and yes you guessed right it was boring. The configuration steps in summary were follows.

• Extracting the private IP of eth0 interface
• Adding few iptable rules with the extracted private IP
• Mounting a ramdisk (which is used by the UltraESB filecache)
• Starting Apache Zookeeper service (which is the leadership election and coordination service used by UltraESB)
• Starting UltraESB service
• Starting AppServer service (which is AS2Station front-end)

My good friend Janaka, suggested me that I should try to use an startup script to get this done. Turns out it was pretty easy. Let me share the steps with you all as it might be useful to some of you as well.

Creating the script

1. First we need to create the script. I created mine by the name setup-script.sh in /var/tmp/ directory.

#!/bin/bash
echo -n "" > /var/tmp/setup-script.out
echo "The time the script run was --> `date`" > /var/tmp/setup-script.out
echo 'Extracting private ip' >> /var/tmp/setup-script.out
PRIVATE_IP=$(curl http://169.254.169.254/latest/meta-data/local-ipv4)
echo $PRIVATE_IP >> /var/tmp/setup-script.out

echo 'Applying iptable rules' >> /var/tmp/setup-script.out
iptables -A FORWARD -d $PRIVATE_IP -p tcp --dport 443 -j ACCEPT >> /var/tmp/setup-script.out
iptables -t nat -A PREROUTING -p tcp --dport 443 -j DNAT --to-destination $PRIVATE_IP:8443 >> /var/tmp/setup-script.out
iptables -t nat -A POSTROUTING -j MASQUERADE >> /var/tmp/setup-script.out
echo 'Appled following iptable rules' >> /var/tmp/setup-script.out
iptables -S >> /var/tmp/setup-script.out
echo 'Appled NAT following iptable rules' >> /var/tmp/setup-script.out
iptables -S -t nat >> /var/tmp/setup-script.out

echo 'Mounting ram disk' >> /var/tmp/setup-script.out
umount /tmp/ram >> /var/tmp/setup-script.out
mount -t tmpfs -o size=512m tmpfs /tmp/ram >> /var/tmp/setup-script.out

#echo 'Switching to adrt user' >> /var/tmp/setup-script.out
sudo su - adrt >> /var/tmp/setup-script.out

service zookeeper start >> /var/tmp/setup-script.out
echo 'Sleeping 1m after zookeeper start command' >> /var/tmp/setup-script.out
sleep 1m
service ultraesb stop >> /var/tmp/setup-script.out
service appserver stop >> /var/tmp/setup-script.out
echo 'Sleeping 1m after ultraesb and appserver stop commands' >> /var/tmp/setup-script.out
sleep 1m
service ultraesb start >> /var/tmp/setup-script.out
echo 'Sleeping 1m after ultraesb start command' >> /var/tmp/setup-script.out
sleep 1m
service appserver start >> /var/tmp/setup-script.out
echo 'Sleeping 1m after appserver start command' >> /var/tmp/setup-script.out
sleep 1m
service zookeeper status >> /var/tmp/setup-script.out
service ultraesb status >> /var/tmp/setup-script.out
service appserver status >> /var/tmp/setup-script.out
echo 'All should be good to go' >> /var/tmp/setup-script.out

2. Then we need to give executable permissions for the script file.

chmod +x /var/tmp/setup-script.sh

Creating new systemd service unit

Now we have to create service file. I created a file by the name setup.service in /etc/systemd/system/ directory.

[Unit]
Description=This is a setup script
After=network.target
After=systemd-user-sessions.service
After=network-online.target

[Service] Type=simple ExecStart=/var/tmp/setup-script.sh TimeoutStartSec=0 [Install] WantedBy=default.target

In this file,

After= : If the script needs any other system facilities (networking, etc), modify the [Unit] section to include appropriate After=, Wants=, or Requires= directives.
Type= : Switch Type=simple for Type=idle in the [Service] section to delay execution of the script until all other jobs are dispatched
WantedBy= : target to run the sample script in

Enable the systemd service unit

# systemctl daemon-reload

# systemctl enable setup.service

# systemctl start setup.service

# systemctl reboot