{"id":1640,"date":"2015-08-23T20:14:56","date_gmt":"2015-08-24T02:14:56","guid":{"rendered":"http:\/\/dev.iachieved.it\/iachievedit\/?p=1640"},"modified":"2015-08-23T20:14:56","modified_gmt":"2015-08-24T02:14:56","slug":"using-monit-with-node-js-and-pm2","status":"publish","type":"post","link":"https:\/\/dev.iachieved.it\/iachievedit\/using-monit-with-node-js-and-pm2\/","title":{"rendered":"Using Monit with Node.js and PM2"},"content":{"rendered":"

As I’ve said before<\/a>, I’m a bit of a whore when it comes to learning new languages and development frameworks. So it comes as no surprise to myself that at some point I’d start looking at Node.js<\/a> and JavaScript<\/a>.<\/p>\n

I have another confession to make. I hate JavaScript, even more so than PHP. Nothing about the language is appealing to me, whether its the rules about scoping and the use of var<\/code> or the bizarre mechanism by which classes are declared (not to mention there are several ways). Semicolons are optional, kind of<\/i>, but not really. I know plenty of developers who enjoy programming in Objective-C, Python, Ruby, etc.; I have never met anyone<\/i> who says “Me? I love JavaScript!” Well, perhaps a web UI developer whose only other “language” is CSS or HTML. In fact, a lot of people go out of their way to articulate why JavaScript sucks<\/a>.<\/p>\n

So along comes Node.js, which we can all agree is the new hotness. I’m not sure why<\/i> it is so appealing. JavaScript on the server! Event-driven programming! Everything is asynchronous and nothing blocks! Okay, great. I didn’t really ask<\/i> for JavaScript on the server, and event-driven programming is not new. When you develop iOS applications you’re developing in an event-driven environment<\/a>. Python developers have had the Twisted<\/a> framework for years<\/i>. The venerable X<\/a> system is built upon an event loop. Reading the Node.js hype online one would think event-driven callback execution was invented in the 21st century.<\/p>\n

Of course, the Node.js community is also reinventing the wheel in other areas as well. What do the following have in common: brew<\/code>, apt-get<\/code>, rpm<\/code>, gem<\/code>, easy_install<\/code>, pip<\/code>. Every last one is a “package manager” of some sort, aimed at making your life easy, automagically downloading and installing software along with all of its various dependencies onto your system. A new framework is nothing without a package manager that it can call its own, thus the Node.js world gives us the Node Package Manager<\/a>, or npm<\/code>. That’s fine. I like to think of myself as a “full-stack developer”, so if I need to learn a new package manager and all of its quirks, so be it. <\/p>\n

Unfortunately it didn’t stop there. Node.js has its own collection of application “management” utilities; you know, those helper utilities that aim to provide an “environment” in which to run your application. Apparently Forever<\/a> was popular for some time until it was displaced by PM2<\/a>, a “Production process manager for Node.js \/ io.js applications”<\/p>\n

I’m not quite sure when it became en vogue to release version 0 software for production environments, but I suppose it’s all arbitrary (hell, Node.js is what, 0.12?) But true to a version 0 software release, PM2 has given me nothing but fits in creating a system that consistently<\/i> brings up a Node.js application upon reboot. Particularly in machine-to-machine (M2M<\/a>) applications this is important; there is frequently no opportunity to ssh into a device that’s on the cellular network and installed out in an oil field tank site. The system must be rock-solid and touch free once it’s installed in the field.<\/p>\n

To date the most pernicious bug I’ve come across with PM2 is it completely eating the dump.pm2<\/code> file that it ostensibly uses to “resurrect” the environment that was operating. A number of people have reported this issue<\/a> as well. If I can’t rely on PM2 to consistently restart my Node.js application, I need something to watch the watchers. So who watches the watchers? Monit<\/a> of course.<\/p>\n

Because PM2 refused to cooperate I decided to utilize monit to ensure my Node.js application process was up and running, even after a reboot. In this configuration file example I am checking my process pid (located in the \/root\/.pm2\/pids<\/code> directory) and then using pm2 start<\/code> and pm2 stop<\/code> as the start and stop actions.<\/p>\n

NB<\/b>: Monit executes its scripts with a bare bones environment. If you are ever stumped by why your actions “work on the command line but not with monit”, see this this<\/a> Stack Overflow post. In the case of PM2, it is critical that the PM2_HOME<\/code> environment variable be set prior to calling pm2<\/code>.<\/p>\n

The first iteration of my monit configuration looked like this:<\/p>\n

\r\ncheck process node_app with pidfile \/root\/.pm2\/pids\/node_app-0.pid\r\n  start program = \"\/bin\/bash -lc 'cd \/root\/node_app && PM2_HOME=\/root\/.pm2 \/usr\/bin\/pm2 startOrRestart processes.json'\"\r\n  stop program = \"\/bin\/bash -lc 'cd \/root\/node_app && PM2_HOME=\/root\/.pm2 \/usr\/bin\/pm2 stop processes.json'\"\r\n<\/pre>\n
Only if this were sufficient, but it isn’t.<\/p>\n
For some reason PM2 insists on appending a process ID to the pidfile filename (perhaps for clustering where you need a bunch of processes of the same name), so a simple pidfile check won’t suffice.  Other folks even went to the Monit lists looking for wildcard pidfile support<\/a> and quoted PM2 as the reason why they felt they needed it.<\/p>\n
So, now our monit configuration takes advantage of the matching<\/code> directive and looks like this:<\/p>\n
\r\ncheck process node_app matching \/root\/node_app\/app.js\r\n   start program = \"\/bin\/bash -lc 'cd \/root\/node_app && PM2_HOME=\/root\/.pm2 \/usr\/bin\/pm2 startOrRestart processes.json'\"\r\n   stop program  = \"\/bin\/bash -lc 'cd \/root\/node_app && PM2_HOME=\/root\/.pm2 \/usr\/bin\/pm2 stop processes.json'\"\r\n<\/pre>\n
Granted, we should not<\/i> be running as root<\/code> here.  Future iterations will move the applications to a non-privileged user, but for now this gives us a system that successfully restarts our Node.js applications after a reboot.  PM2 is a promising tool and definitely takes care of a lot of mundane tasks we need to accomplish to daemonize an application; unfortunately it is a little rough around the edges when it comes to consistent actions surrounding the ability to survive system restarts.  Don’t take my word for it:  read the Github issues<\/a>.<\/p>\n
Conclusion<\/h3>\n
A rolling stone gathers no moss.  The more things stay the same, the more things change (or is it the other way around?).  I have nothing against new frameworks, but there are times when being an early adopter requires one to pull out a tried-and-true applications to get the job done.  In this case our old friend Monit helps up fill in the gaps while Node.js and PM2 mature.<\/p>\n","protected":false},"excerpt":{"rendered":"
As I’ve said before, I’m a bit of a whore when it comes to learning new languages and development frameworks. So it comes as no surprise to myself that at some point I’d start looking at Node.js and JavaScript. I have another confession to make. I hate JavaScript, even more so than PHP. Nothing about […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[21,19,14],"tags":[],"class_list":["post-1640","post","type-post","status-publish","format-standard","hentry","category-devops","category-linux","category-node-js"],"_links":{"self":[{"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/posts\/1640"}],"collection":[{"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/comments?post=1640"}],"version-history":[{"count":36,"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/posts\/1640\/revisions"}],"predecessor-version":[{"id":1676,"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/posts\/1640\/revisions\/1676"}],"wp:attachment":[{"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/media?parent=1640"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/categories?post=1640"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/dev.iachieved.it\/iachievedit\/wp-json\/wp\/v2\/tags?post=1640"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}