SYNOPSIS
Safe code hotswap for zero downtime re-deploys.
BUILD STATUS
MOTIVATION
An application in production should not need to be stopped in order to
utilize new code.
DESCRIPTION
liveswap is a library that helps you update an application’s code without stopping it.
It also ships with a command-line tool and it doesn’t impose any special requirements
or conventions on your application code.
It works by creating a light-weight master process that runs your application code as
worker processes. It then starts listening for instructions.
When you send an upgrade instruction, workers take turns disconnecting their underlying
servers. When a server is disconnected, it lets the old connections finish up, but no
new connections are accepted. When all of the worker’s connections have been closed, it
will be retired and a new one will be created using the new code. For more in depth
information read this blog post.
USAGE
Install
npm install liveswap -g
Example
Using the node.js hello world example, in a filed named index1.js...
First Version (Sample Code)
var http = require('http')
http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/plain'})
res.end('Hello World\n')
}).listen(1337, '127.0.0.1')
console.log('Server running at http://127.0.0.1:1337/')
Startup
Start the application using liveswap from the command-line...
liveswap -s index1.js
Alternatively, start liveswap programmatically...
var liveswap = require('liveswap')
liveswap('./index1.js')
Second Version (Sample Code)
Now we have an updated version of the code in index2.js...
var http = require('http')
http.createServer(function (req, res) {
res.writeHead(404, {'Content-Type': 'text/plain'})
res.end('Not Found\n')
}).listen(1337, '127.0.0.1')
console.log('Server running at http://127.0.0.1:1337/')
Live Update
Update the current code by sending an update command to the server.
liveswap -u ./index2.js
After sending an update message the worker processes will wait for
any current connections to end before restarting with the new code.
CLI Options
Options:
-p, --port <port> specify the liveswap server port. [default: 3000]
-a, --address <address> specify the ip address to run on. [default: "127.0.0.1"]
-f, --forks <number> specify how many worker processes to spawn [default: 2]
-u, --upgrade [<path>] specify the source code to upgrade to.
--pre-upgrade <path> a module to handle pre upgrade logic.
-k, --kill kill all forked worker processes and respawn.
-d, --die kill all forked worker processes and quit master process.
-m, --message <message> send a message to all the forked worker processes.
-s, --start <path> start a node process cluster.
-H, --head <path> path to HEAD file
-z disable zero-downtime, upgrade will kill processes
-v, --version print program version and exit
Pre-upgrade allows you to require a module that will be executed before each
time the upgrade happens.
liveswap --pre-upgrade ./pull.js --start ./index1.js
The pre-upgrade module should export a single function as its interface.
Here's an example of what that module might look like:
function preupgrade(data, callback) {
console.log('executing pre-upgrade script...');
var err, value = data.value;
try {
// execute pre-upgrade code
} catch (e) {
err = e.toString();
}
callback(err, value);
}
module.exports = preupgrade;
API
liveswap(opts)
The main export of this library accepts an options object or a string. If a
string is specified, it will be interpreted as the target option.
[option] { target: <String> }
[option] { port: <Number> }
[option] { address: <String> }
[option] { forks: <Number> }
[option] { head: <String> }
[option] { 'pre-upgrade': <String> }
[option] { 'zero-downtime': <Boolean> }
liveswap({
target: './index.js',
port: 9008,
address: '0.0.0.0',
forks: 2,
head: '/tmp/HEAD',
'pre-upgrade': './pull.js',
'zero-downtime': false
})