Since we started the node application manually in the terminal, closing the ssh connection or hitting Ctrl + C on the keyboard will stop the node process, and therefore our Hello World application will not work anymore.
Amazon Linux, unlike standard Red Hat-based distributions, comes with a system called Upstart.
It is fairly easy to use and provides a couple of extra features that traditional System V bootup scripts don't have, such as the ability to respawn a process that died unexpectedly. To add an Upstart configuration, you need to create a file inside /etc/init on the EC2 instance.
Here is the code to insert in /etc/init/helloworld.conf:
description "Hello world Deamon"
# Start when the system is ready to do networking.
start on started elastic-network-interfaces
# Stop when the system is on its way down.
stop on shutdown
respawn
script
exec su --session-command="/usr/bin/node /home/ec2-user/helloworld.js" ec2-user
end script
If you are familiar with Upstart outside of AWS, you might have used start on runlevel [345]. The problem with that in AWS is that your network comes from Elastic Network Interface (ENI), and if your application starts before this service, it might not be able to connect to the network correctly.
[ec2-user@ip-172-31-22-234 ~]$ sudo wget http://bit.ly/2vVvT18 -O /etc/init/helloworld.conf
--2017-02-01 00:20:03-- http://bit.ly/2vVvT18
Resolving bit.ly (bit.ly)... 69.58.188.39, 69.58.188.40
Connecting to bit.ly (bit.ly)|69.58.188.39|:80... connected.
HTTP request sent, awaiting response... 301 Moved Permanently
Location: https://raw.githubusercontent.com/EffectiveDevOpsWithAWS/code-snippets/master/helloworld.conf [following]
--2017-02-01 00:20:03-- https://raw.githubusercontent.com/EffectiveDevOpsWithAWS/code-snippets/master/helloworld.conf
Resolving raw.githubusercontent.com (raw.githubusercontent.com)... 199.27.76.133
Connecting to raw.githubusercontent.com (raw.githubusercontent.com)|199.27.76.133|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 286 [text/plain]
Saving to: '/etc/init/helloworld.conf'
/etc/init/helloworld.conf 100%[=============================================================>] 286 --.-KB/s in 0s
2017-02-01 00:20:03 (67.4 MB/s) - '/etc/init/helloworld.conf' saved [286/286]
[ec2-user@ip-172-31-22-234 ~]$
We can now simply start our application, as follows:
[ec2-user@ip-172-31-22-234 ~]$ sudo start helloworld helloworld start/running, process 23090 [ec2-user@ip-172-31-22-234 ~]$
As expected, http://your-public-dns-name:3000 still works, and this time, we can safely close our ssh connection.