Clusterify your NodeJS applications and deploy without downtimes. Just like that.
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An handy tool for your node servers and 0 downtime needs.

ClusterJS will take your app and spawn it in a node-cluster with as many workers you want.

You can reload the whole cluster sending a simple signal: ClusterJS will go through all your workers, reloading them one by one.

~/projects/clusterjs (master ✔) ᐅ clusterjs
Cluster.js help:

Usage: clusterjs [path to app] [options]

 --workers   Defines how many workers we should launch (Default: CPU count)
 --reloadon  On Which signal will the cluster be reloaded (Default: SIGUSR2)


It is recommended to install the package globally:

npm install -g clusterjs


Suppose you have an app running on an app.js file, you can simply decide to start it with clusterjs:

clusterjs app.js

This will start a cluster of as many apps as CPU cores you have on your machine; to change the number of workers, simply specify it when launching the cluster:

clusterjs app.js --workers 5

WARNING if your path contains a symlink, clusterjs will need the full path to your app

clusterjs /path/to/your/app.js

You can reload the cluster, achieving zero-downtime deployments by issuing a SIGUSR2 command to the master process:

~/projects/clusterjs (master ✔) ᐅ ps aux | grep cluster.js
29571  2.0  0.1 659236 10440 pts/4    Sl+  23:21   0:00 node ./bin/cluster.js test/testApp/app.js
29573  1.5  0.1 656160  8564 pts/4    Sl+  23:21   0:00 /home/local/bin/node /home/projects/clusterjs/bin/cluster.js test/testApp/app.js
29574  2.0  0.1 656160  8564 pts/4    Sl+  23:21   0:00 /home/local/bin/node /home/projects/clusterjs/bin/cluster.js test/testApp/app.js
29576  1.5  0.1 656160  8564 pts/4    Sl+  23:21   0:00 /home/local/bin/node /home/projects/clusterjs/bin/cluster.js test/testApp/app.js
29577  1.5  0.1 656160  8564 pts/4    Sl+  23:21   0:00 /home/local/bin/node /home/projects/clusterjs/bin/cluster.js test/testApp/app.js
29582  0.0  0.0  13636   984 pts/5    S+   23:21   0:00 grep cluster.js

~/projects/clusterjs (master ✔) ᐅ kill -SIGUSR2 29571

This will gracefully reload your cluster, updating the app without any downtime.

You can also customize the signal used to reload the cluster:

clusterjs app.js --workers 5 --reloadon SIGUSR2

If you want to actually shutdown the app, simply issue a SIGTERM or a SIGQUIT (ie. kill 29571).

As a module

You can also use cluster.js as a module in your userland code by simply requiring it:

var clusterjs = require('clusterjs');

cluster('app.js', 5, 'SIGUSR2');

Have a closer look

You can use the simple dummy server included in the tests/testApp directory if you need to experiment:

git clone

cd clusterjs

./bin/cluster.js test/testApp/app.js

Thanks to

Well, the biggest effort was made by Jonathan Warner who explained how easily you could achieve ZDD with node.

We polished the code a bit as we found out that it had some glitches but the main idea remains the same (so yeah, thanks Jax!).


ClusterJS is released under the MIT license.