Introduction
When deploying a web application to a Droplet, it might be tempting to simply use the same kind of setup as is used in development, i.e. starting the server by running “ruby app.rb” or “node server.js” in a terminal. This is simple and easy, while providing visible logs. One might even use “screen” or “tmux” or “nohup” to have it keep running even when the SSH session is dropped. This is dangerous: what happens if the server crashes and no one is around to restart it?
One could use forever and crontab to take care of this. This tutorial presents a more robust, albeit more complex, solution. Using systemd (available on Arch and Fedora, and CentOS in the future), web applications can be thoroughly managed: logs, uptime, resources and security through cgroups, and advanced daemon startup can all be accessed, controlled and fine-tuned in a unified manner.
This tutorial uses a simple Node.js application, but is applicable to most, if not all, others as well (be they Ruby, Python, etc). For PHP web applications, it is recommended to use a more specialized LAMP or LEMP stack instead.
Commands will be provided for both Fedora and Arch, do keep a lookout for which is which to avoid misconfiguration and/or confusion. When not indicated, the command is the same for both systems. It is also recommended you read through the entire tutorial before attempting it step-by-step, so as to get an idea of what it entails and whether it is appropriate for your situation.
System Preliminaries
A server with systemd. Arch Linux and Fedora droplets are configured thus by default.
Nginx, to be used as a reverse-proxy http and websocket server.
Git, to install nvm, and to pull your application if using git.
Root access. It is also possible to login as a normal user and sudo all commands, or to su – or sudo su – to a root prompt.
Install packages
Arch:
# pacman -Sy
# pacman -S nginx git
Fedora:
# yum install nginx git
Application Preliminaries
These are settings you can customise to your liking, but they have to be decided upon and set before starting.
User
The application will run in its own separate user account. Pick a name, it should relate to the application to make it easy to remember and maintain. Here, srv-node-sample is used.
# useradd -mrU srv-node-sample
Port
To avoid conflicts, pick a high port. Here, “15301” is used.
Application Setup
Start by installing what is necessary for the application to run. For Node.js (and Ruby, Python…), there are two choices: either use the system’s runtime, or a user-specific installation (e.g. using nvm, rbenv, RVM, virtualenv, etc).
Using the system node
Arch:
# pacman -S nodejs
Fedora:
# yum install nodejs
Using a user-specific install
This has to be installed in the application’s home directory, i.e. /home/srv-node-sample, which is most easily done by logging in as that user:
# su srv-node-sample
$ cd
$ curl https://raw.github.com/creationix/nvm/master/install.sh | sh
$ source ~/.nvm/nvm.sh
$ nvm install 0.10
$ nvm alias default 0.10
Then take note of where the node binary is installed:
$ which node
/home/srv-node-sample/.nvm/v0.10.22/bin/node
Deploy your application
While logged in to srv-node-sample, deploy your code. This is an example only, your process will vary.
$ git clone git@server.company.tld:user/repo.git .
$ npm install
$ grunt deploy
For this tutorial, the following sample application is used:
js
var http = require('http');
http.createServer(function(req, res) {
res.end('<h1>Hello, world.</h1>');
}).listen(15301);
Then return to root:
$ exit
Nginx Setup
This tutorial only briefly covers the configuration necessary, for a more thorough tutorial on configuring Nginx, see “How to Configure the Nginx Web Server” or the nginx manual.
Place this in your server block:
location / {
proxy_pass http://localhost:15301/;
proxy_set_header Host $host;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
}
Then set up its daemon:
# systemctl enable nginx
# systemctl restart nginx
Systemd Setup
Create a service file for the application, in /etc/systemd/system/node-sample.service.
There’s a few variables that need to be filled in:
[node binary] This is the output of “which node” as the srv-node-sample user. Either /usr/bin/node or the ~/.nvm/... path noted above.
[main file] This is the main file of your application. Here, ‘index.js`.
Don’t forget to replace srv-node-sample!
[Service]
ExecStart=[node binary] /home/srv-node-sample/[main file]
Restart=always
Standard=syslog
StandardError=syslog
SyslogIdentifier=node-sample
User=srv-node-sample
Group=srv-node-sample
Environment=NODE_ENV=production
[Install]
WantedBy=multi-user.target
Now start the service:
# systemctl enable node-sample
# systemctl start node-sample
Usage
Status
# systemctl status node-sample
node-sample.service
Loaded: loaded (/etc/systemd/system/node-sample.service; enabled)
Active: active (running) since Fri 2013-11-22 01:12:15 UTC; 35s ago
Main PID: 7213 (node)
CGroup: name=systemd:/system/node-sample.service
└─7213 /home/srv-node-sample/.nvm/v0.10.22/bin/node /home/srv-nod...
Nov 22 01:12:15 d02 systemd[1]: Started node-sample.service.
Logs
# journalctl -u node-sample
-- Logs begin at Thu 2013-11-21 19:05:17 UTC, end at Fri 2013-11-22 01:12:15 UTC. --
Nov 22 01:12:15 d02 systemd[1]: Starting node-sample.service...
Nov 22 01:12:15 d02 systemd[1]: Started node-sample.service.
Nov 22 01:12:30 d02 node-sample[7213]: Sample message from application
Restart, stop, etc
Force a restart:
# systemctl restart node-sample
Stop the application:
# systemctl stop node-sample
The application will be automatically restarted if it dies or is killed:
# systemctl status node-sample
node-sample.service
Loaded: loaded (/etc/systemd/system/node-sample.service; enabled)
Active: active (running) since Fri 2013-11-22 01:12:15 UTC; 35s ago
Main PID: 7213 (node)
CGroup: name=systemd:/system/node-sample.service
└─7213 /home/srv-node-sample/.nvm/v0.10.22/bin/node /home/srv-nod...
Nov 22 01:12:15 d02 systemd[1]: Started node-sample.service.
# kill 7213
# systemctl status node-sample
node-sample.service
Loaded: loaded (/etc/systemd/system/node-sample.service; enabled)
Active: active (running) since Fri 2013-11-22 01:54:37 UTC; 6s ago
Main PID: 7236 (node)
CGroup: name=systemd:/system/node-sample.service
└─7236 /home/srv-node-sample/.nvm/v0.10.22/bin/node /home/srv-nod...
Nov 22 01:54:37 d02 systemd[1]: node-sample.service holdoff time over, sch...t.
Nov 22 01:54:37 d02 systemd[1]: Stopping node-sample.service...
Nov 22 01:54:37 d02 systemd[1]: Starting node-sample.service...
Nov 22 01:54:37 d02 systemd[1]: Started node-sample.service.
The PID has changed, showing the application has indeed been killed and restarted.
Websockets
If the application uses websockets, the following lines have to be added to the Nginx configuration:
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
proxy_http_version 1.1;
and Nginx has to be reloaded:
# systemctl reload nginx
