How to get master to fork workers from new release?

[sandinmyjoints]

This is more of a conceptual question than an issue with recluster per se, so sorry about that, but any guidance would be appreciated. If I am managing deployment by directories that contain releases, then when I do a new release, how do I tell cluster to fork the new workers from the path to the new release code?

In other words:

Say release A is in /var/deploy/app/A, and symlink /var/deploy/app/current/ points to it. My app lives in app.js so my file argument to recluster is a relative path:
var cluster = recluster("app.js");.

My simple cluster master script lives in cluster.js. I start up a master process via cd /var/deploy/app/A ; node cluster.js which forks a few app.js workers using the code in /var/deploy/app/A. The cwd of the master and the workers is /var/deploy/app/A.

Now I deploy release B to /var/deploy/app/B and update /var/deploy/app/current to point there. I send SIGUSR2 to master. master's cwd is still /var/deploy/app/A, so it is going to fork new workers from there rather than from /var/deploy/app/B.

One solution to this is:

1. explicitly use the /current symlink when starting the cluster master: cd /var/deploy/app/current ; node /var/deploy/app/current/cluster.js.
2. specify the file argument to cluster using the symlink from the master process:

var workerPath = process.argv[1].replace("cluster", "app");
var cluster    = recluster(workerPath);

Because the symlink is updated to the new release before SIGUSR2 is sent, the new workers will be forked from the new release.

In practice, I am using Chef and Upstart which complicates things somewhat. But ultimately I want to send a signal to the master process (via service <app name> reload) that will cause it to fork new workers from the new code release that Chef just deposited onto the server. Without the symlink, I haven't thought of a way to keep the same master process around but get it to fork workers from the new code. Do you have any thoughts on this?

[spion]

I'm afraid that symlinks are the only way for now. Thats because setupMaster from the cluster module can only be called once.

However, this can probably be worked around by writing a generic worker.js that takes the path to the script from env, then simply require()s it. If we do that, then .reload() could take an optional argument - the path to the new worker module.

But this still won't solve SIGUSR2-based reloads by itself. Your cluster.js will have to ask for configuration (e.g. to open and read a config file - or perhaps to open a unix socket where it can take reload commands). recluster wont do that as it aims to be a minimal library which can be used in any context - but once it supports arguments to cluster.reload this should be easy to implement.