Introduction

PM2 is a great tool that can help you manage not just your processes when they are running but also env types, vars, and configs. I still find many questions around the basic operation of the tool around the internet such as stackoverflow and other boards. So this article will cover how I setup most of my projects using PM2; short, sweet, and to the point. 

Setting up a quick app

First let's create a quick API that returns hello world as a response. Move into an empty directory and create a file called API.js and put the following into it. 

Starting up PM2

Within the project directory install PM2 as a package globally and into your project dependencies npm i pm2 -g; npm i pm2 --save 

You have now installed all you need to setup production level process running and environment control ( with enough configs and a pipeline of course ). With the latest versions of PM2 the tool comes with the ecosystem command that will help us generate what we need to create and application definition for our small API. However to see some immediate action you can just run : pm2 start API.js 

Confirm that your API start by visiting localhost:3000/ again and checking if the text "Hello World!" is rendered. You can see that your process starts up and you get a nice looking table print out with some facts about your process. You can shut down your process by running pm2 delete API .

Note: Delete will remove the application entirely from PM2's registry; however you can also use  pm2 stop API  and it will stop the application but not remove it so you can use  PM2 start API  to start it up again. In our case however we want PM2 to forget about our process since we are going to create an ecosystem config for it and start it that way.

Setting up ecosystem.js

Now that we have shown that pm2 will start our API, and that our API still returns what we expect we can setup a more maintainable and useful way to start our app. Within the project app run pm2 ecosystem 

This will generate a application definition with a few other things inside of a ecosystem.js file that it created. Lets go through the sections that get generated and a quick over view of what we can do with them.

Apps Section

This section is arguably the most important for getting your application up and running. This is where you will define how your application runs, environment specific vars, logging behaivors, and more. In addition you can define multiple apps in the same ecosystem file; this can be used to start up co-processors, log streamers, queue managers, and more.

I will go over a few of the fields that can be used with an app definition that I think are some of the most common or useful.

Instances - Int

The number of app instance to be launched. This can be set to -1 to start as many processes as the system has CPU cores subtract 1. I use this in docker setups a lot because I can allow the application to consume the entire container since that is what it is dedicated to. 

node_args - String Array

This is an array of arguments that will be passed to the actual node execution which allows you to pass things like the --harmony flags for older node version or things such as debug flags.

error_file, out_file, pid_file - String ( directory/file path )

These values point to the directory and file name that you want pm2 to export the generated logs from your application to. This is valuable again in the containerization scenario when you want your logs to go specific places to be picked up by log aggregation systems. 

max_restarts - Int

This is the number of consecutive unstable restarts (less than 1sec interval or custom time via min_uptime) before your app is considered errored and is stopped from being restarted any more. This is a great option to allow your application to show that it can't connect to mission critical services or API's at start up time. I currently use this as a flag that something is very wrong when a new deploy goes out.

max_memory_restart - String

This option allows a max memory limit to be set that, when hit, causes PM2 to restart you application automatically. Useful to ensure a rogue process doesn't bring down boxes if they suddenly get a ton of load or the process simply goes off the rails. The value of this field is a String that uses the normal volume types M = megabyte, b = byte, so if you wanted the max memory to be 400 megabytes then the value here would be "400M".

min_uptime - String

This option lets pm2 know that your application should be up and stable for x amount of seconds before being considered started instead of in the starting state. This can be important if your project has to connect to a service and timeouts are an issue or there is a lengthy read operation on disk, etc.

env - Object Key/Val

The env object is what allows you to define environment level vars based on the environment flag you give PM2 at startup time. the plain env field is an object that contains values that will be available all of the time regardless of the environment that is passed to pm2. 

Any field that follows the pattern env_${myEnvironmentName} is considered a valid env setting and the values defined within will only be available when the --env flag us used and a valid key that matches the following rules is found. For example a env_production env object then allows you to use the following command pm2 start ecosystem.js --env production 

Note I think it is worth mentioning how you get to these environment variables. All of these keys will be available via the global process variable. So to get the env NODE_ENV to see what mode the application has been started in you would use process.env.NODE_ENV.

Here is an example of all the discussed settings for an application definition. There are plenty more options that you can find in the PM2 docs page.

Deployments Section

As a disclaimer I do not use the PM2 deployment tool in any projects currently aside from deploying to some rasberry pi's I have hooked up on my local network. This is because these days all of my CI/CD pipelines use Docker or run through Heroku. That being said I will give you what I know on how to get deployments working for you via PM2. 

The use case for using the PM2 deployment tool set fits if you have static servers that are not containerized that you don't want to bring down your systems just to do a small update to your application. This is the case at with my home setup where I have node instances running on Rasberry Pi's. 

To setup deployments via PM2 first define your application section with the options you want from the previous section. Then in your ecosystem.js go to the deploy section of the config. Here you will find the two generated deployment options production and dev, these are enviornment configs just like the application definition has; they will be used to define what env your are deploying to. Here there are a few key definitions that need to be flushed out.

user - String

This is the user that the target machine will use to run any commands that are pushed to it via PM2. It must have the approprite permissions to execute the commands ( git pull, npm install, etc ) on the target machine. In addition this is the user that PM2 will attempt to authenticate via ssh using a key on your machine or a key you provide within the deployment configuration ( more on this a little later )

host - String/String Array

The host field can hold a single host or an array of hosts. These hosts can be IPs or hostnames that will get resolved via DNS. The machine doing the deploy must have an SSH key for these machines so that authentication can occur OR a .pem file must be given as part of the deployment config.

key - String

The file location of a .pem file that contains the approprite key to authenticate against the hosts using the User as the username.

ref - String

Ref is the git origin branch that you want to get deployed. Most of the time this will be a "production" branch or something similiar that you merge into when a version has been tagged or something similiar. 

repo - String

The git repository URI that the ref branch is in and the hosts have access to pull from. 

path - String

The path that the git branch will be downloaded into on the host.

pre-setup - String

This field is (a) command(s) to be run BEFORE the git checkout for the branch is done on the host.

post-setup - String

This field is (a) command(s) to be run AFTER the git checkout for the branch is done on the host. This is generally where you would put your npm install, gulp builds, etc.

post-deploy - String

This field is (a) command(s) to be run AFTER the pre and post setups events. This is where you will put your application restart/start command(s)

pre-deploy-local - String

This field is (a) command(s) that will run on the deployment machine, not the hosts that are being deployed to BEFORE it actually fires off the deployments. This is useful for putting deployment configs, alerts, etc into things like slack, emails, etc.

An example of the all these fields for a production env.

Once you have your application running for the first time on the hosts listed in the production deploy config. From a build server ( or your local box ) you can run pm2 deploy ecosystem.js production .

If everything runs successfully you should see a message similiar to : "Deploy Succesful" , you are all done!

Daemonizing your application with PM2 (2.2 >)

PM2 allows you to configure a startup script that will ensure your application comes back up if for some reason a restart or shut down has occured. This is useful again if you have bare metal you are running on that is not containerized or if for some reason you have a very unstable server setup; or have to do rolling restarts of servers for deployments. 

PM2 comes with the pm2 startup command that will out put a command for root to run that will add the approprite config so your application will start on machine startup. You can also pass pm2 an explicit type of startup script to generate if you know your environment OS. Here is the supported options: ubuntu, ubuntu14, ubuntu12, centos, centos6, arch, oracle, amazon, macos, darwin , freebsd, systemd, systemv, upstart, launchd, rcd, openrc. 

Here is an example output from the command :

On a build server you can write some simple awk, grep, or regex to extract the command and run it on the machine that is being provisioned. 

You can read more about process management via things like init.d and more here.

Wrap up

PM2 is a powerful tool for getting things up and running fast, but it also has the staying power for production level applications. I have many applications both at my day job and my personal applications that run using PM2 and KeyMetrics. Some of the deployment management I feel is antiquated by the rising use of containers and the associated services such as AWS, Google Cloud, Heroku, etc but it still has it's place in situations where you don't have the flexiability of a container driven development environment. 

Links :

http://pm2.keymetrics.io/docs/usage/application-declaration/

http://pm2.keymetrics.io/docs/usage/deployment/

http://pm2.keymetrics.io/docs/usage/startup/

Introduction 

To this day I get asked a lot on how I find issues inside my code base, some times even where I put my console.logs(). My answer is that I use a debugger; however almost every time this surprises people in the Node.js/JS community. I thought we had gotten past the strange period of JavaScript as a language where console.log()ing random points in your code base was the way to debug things. 

Apparently I was wrong; at least based on how often I get asked this type of thing.

So in the spirit of hoping to propagate something I strongly feel should be a standard and something every JS developer ( or any type of developer really ) should now how to setup and use, this is a small article on how to use Chromes dev tools to debug your Node.js projects.

Installation and Setup For Node 6.3 & Above

In Node 6.3 we got a native debugger module that Node.js now ships with that is actually developed by the Node team. To use this there is now command flag options that we can pass in when starting our node projects. It will do some simple quality of life things as well, if the same file ans instance are brought down and back up the debugger will reattached itself, which is pretty helpful.

Debugging Just Using Node

When you start your application now you just append a --inspect to the node command and it should do everything needed on the process level. 

node myProject.js --inspect

Next open up chrome and go to about:inspect in the URL bar. This will bring you to a panel that looks like the image here 

You can then click the "Inspect" link under the name and path of your running application and it will open up a standard chrome debugger that is attached to your process.

Debugging using PM2

PM2 is a great process runner that I personally use for all my node related projects. However due to the how PM2 works and handles configurations for projects it requires a little extra work to get running with --inspect. 

An awkward conversation for us all

This won't be a technical example and won't have any example code with it, it is simply a talk. A talk that I don't feel most people are willing to have in today's software development environment; in fact I find most people any higher then a senior engineer flat out refuses to even address most of the time. 

Software Critical Mass.

 Some of you most likely have heard of this and some not, so here is the definition of software critical mass as I see it.

Critical mass - A stage in the software life cycle when the source code grows too complicated to effectively manage without a complete rewrite. At the critical mass stage, fixing a bug introduces one or more new bugs that may or may not be related to the fix directly but was still inadvertently affected.

Impact Vs Cost

Before I get into how to identify your approach to critical mass I'd like to go over some of the cost and issues that come up when discussing it. I talk about critical mass where I am currently employed a fair amount due to the fact that the original software was built in a monolithic way and there are a lot of efforts going into moving it away from that. In those efforts however there is always the question of "Why do we need to redo what is already working.", as a developer that spends 40+ hours a week in the code base my mind and I am sure your mind races with ideas as to why and it all seems obvious. But to those that don't spend the time in that code base such as most managers and C levels, it's not obvious.

Now I am not necessarily bad mouthing the higher ups in various companies because the lack of understanding goes both ways. As a developer you don't always see a lot of the business impact that the stall in new features, updates, etc have on the customer base/revenue. 

This brings us to Impact vs Cost.

Impact is what developers are normally after, and cost is what higher ups are normally worried about. The stance can be switched as well however. The developer is concerned with how much time they put into sorting through a messy code base, and the higher ups are after a meaningful impact. 

Determining Impact 

Impact now has two definitions for us :

1. Director/C level impact - The direct result of a change relative to the user which may create a change in revenue numbers.
2. Developer impact - The ease of developing in the code base to make the changes that can satisfy C level impact ultimately 

This often is brought down to time and cost for what kind of change is proposed. While there is no perfect way to determine this it is often beneficial to determine some base line definitions for what kind of changes will be coming.

For developers/leads

As developers we often say that we would like just to rewrite an entire pieces of the software or even the entire thing without any type of qualifiers on it. This doesn't seem like a very reasonable thing to do from a sky level view of how things work even though it may be entirely the right thing to do code base wise. 

Determining impact for developers should ultimately come down a few factors in my mind :

• Ease of modification
• I generally consider this to be a time based metric. It will take a experiments to get a time but it is worth it. 
• Small spin up time
• Again this can be measured but generally only when you are bringing new people on or starting up a new project.
• Readability
• Developer comfort levels when making changes

While some of these are anecdotal they can still be quantified reasonably via simple things like surveys and simply asking for a score between 1 and 10 every once and a while. I feel these key things are what lead to faster more polished features that require less constant upkeep.

So when you say that you would like to rewrite something try to attach value not on what we as developers would like but what the end result would be and it's value to a C/Director level impact because at the end of the day it's not our call on what initiatives get focused on. Not what we like to hear, but just the way companies work.

For Directors/C levels

If you are a director/C level reading this, then welcome. If not, feel free to forward this on to yours whatever your intention. Lets talk about value and reason to a developer. The primary goal of a developer most of the time is to create a better code base and a better piece of software because that means something that is easier to turn into a service or product to sell ( if they aren't at least attempting to improve things to some degree that is a talk for later ).

Determining the impact of something your developers want to do for whatever reason can be difficult, and some times we aren't the best at communicating why. But it also isn't productive to either side to just ignore them when they come to you, maybe in an angry or ill temperament, and tell you that there is something that seriously needs to be addressed. for one that doesn't make much sense for you to ignore the person you hired to maintain the software and spends their entire work week in it. Two it is a sign that something is unhealthy in both the code base AND your developers base. Developers don't like working in an awful code base.

So impact. Evaluating impact should be a duel effort between you and your team(s), but at a core level a good developer impact should give you a good impact. Now sometimes things just don't line up and you can't let the developers go off and do whatever they want. You obviously can't just spend all your developers time making the code base pretty; but again they shouldn't be ignored.

However to avoid this critical mass issue a compromise must be made. Business value is directly correlated to team value and health which is tied to your code base. So when a developer comes to you and wants to rewrite something, don't just turn them down, attempt a compromise of extended time to work on a Jira ticket to clean things up which should mean less effort and time is required to modify that same feature in the future, which will translate to your own initiatives. 

Or if you want to go a level deeper, ask what new functionality can come of these changes and how it will actually improve the code base and support future features. Through this you can then gain even more value for an initiative because the chances of what a developer would like to improve crossing into new planned features or changes is pretty likely. 

Recognizing Critical Mass Approach

Culture

One sure fire way to recognize critical mass is the fact that most of the developers constantly complain about how things were written awful and it is no use trying to fix any of it. When that starts to crop up I would say once every two week basis you are on the door step of critical mass. 

It is worth mentioning that some developers are just always out to say everything is awful but never really participate in fixing anything, it has become their work ritual. Those types in my view should be removed from most scenarios but we all know at least one. Why this isn't a real measurable thing it can be pretty easy to take 10 minutes of random peoples time every once and while to find out how they feel about the code base.

Work load and ticket branching

For a more quantifiable way to measure critical mass approach is through ticket tracking. Now as a developer I often find ticket tracking one of the most infuriating things to deal with, especially with complex system changes. But it does have a place; this is one of them. If it can be identified that often times a fix, that is indeed a fix and makes something work correctly, breaks something else and creates a work load for your team more then the work it took to make the fix: your code base is approaching that critical mass. It's this type of occurrence that I encourage managers, leads, etc to really look out for. This type of metric is pretty easy to track given tools such as Jira because you can see things like spring overflow ( assuming all your Jira flows work ).

Now the tickets spawning tickets ( Ticket Branching ) thing is common in most companies but it depends on the percentage of the time a ticket will generate more work then it took to close. Ticket branching as I've named it, should really be under a 1/5 ratio from my experience. Now depending on how big the team is and the product that can be adjusted, but I have been able to take that anywhere I've gone so far. 

There are numerous ways to deal with this particular issue, but that list is simply to long to be gone over for every type of situation; this is simply a warning to make people aware of what to watch for.

Wrap up

It's been a lengthy and most likely painful read, I know. Company politics, C/Director levels, listening to developers, and attempting to quantify is a hard part of the job, one that I see ignored more times than not. I am sure there are plenty of opinions some agreeing and some not, and that is fine. This isn't a guide, to do list, or one stop shop for how to run anything; simply my own observations on how software companies are run these days. 

When it comes right down to it, the fact is that higher ups need to come down, and devs need to come up for air so something can finally get agreed upon, explained, and defined for things to move forward. It's hard, and this type of thing isn't something most people would say they have time for, but maybe that is part of the problem.

Critical mass can kill software faster then almost anything I've seen; why don't we all work together to make it less of an issue?

I will leave you with questions to ask yourself depending on where you are in a company, give these a good hard thought and be honest; then maybe change a few things here and there to see if you can make a clearer line of communication regardless of the level you are at.

• C/Director level
• When was the last time you had a honest talk with a developer ( not a manager ) about the state of the code base?
• Developer
• When was the last time you gave a thought to the companies stock, online reviews, and the current market?

Introduction rant

Over the course of the last few months I have been in charge of developing a sustainable and observable project structure for Node micro services. While I have done many things like this before, each environment and ecosystem that you develop in provides different challenges. Using PM2 for your node projects is not anything revolutionary if you live in the world of Node development; however using PM2 to its fullest can be a bit mystifying depending on your development requirements. 

One requirement I came across with my latest endeavors is when your employer doesn't want to invest into Kyemetrics as a service, there is a limiting technical factor that doesn't allow direct reporting to the Keymetrics platform, or you simply get dismissed by the higher ups but there is still the requirement for the existing technology ( such as an orchestration system ) to be able to pull metrics from your service/app.

It is the last situation above, that lead me into the deeper parts of the PM2 ecosystem tools and how to expose things not only that came stock with the metric reporter, but very specific things that I wanted to expose for one reason or another.

At this point if you don't have a understanding of what PM2 is or what it does for you, I suggest you read this before moving forward.

What is PMX?

PMX is a module for the PM2 runner that implements an API that allows exposure of metrics tied to the process sandboxes and layer 4 of the OSI model. This allows for the monitoring of various metrics associated with each application process being run.

That is really just a lot of talk to say that it can let you know when your Node instances are on fire. Also it can reveal useful patterns that can show you data that can lead to change on how you scale your instance or utilize certain resources.

Starting a small example

Download Sample Code

Let us get to the good stuff and actually show how it is used and the code implemented. It is actually a pretty painless process assuming you are already using PM2 to manage your project. If you don't want to bother going through the steps of creating your own project you can download the sample code above.

Installation and setup

For this particular article we will assume our project structure looks like this, you can also just download the code example for this article.

• myProject
• metricsDefinitions
• count.js
• middleware
• countMetric.js
• node_modules
• package.json
• bootstrap.js

and it will be using the following libraries for our example build out : pm2, pmx, and express. You can install these by running

 npm install pm2 pmx express --save 

After your dependencies have been installed modify your package.json scripts section to mimic the following

This adds the ability for your npm start command to also start the metrics API if your app start up was successful. Really we are just wrapping the PM2 startup commands here but leveraging the npm scripts section to ensure that PM2 exits successfully for starting your app is just good practice in my book. You can just do the whole thing in the start script command as well with pm2 start bootstrap.js; pm2 web which will always bring up the metrics API regardless of your app state which can be useful if you are going to use it to check the status of you Node instance(s).

Finally writing some code

Now we can get to actually adding code to files. We will be creating a small server that keeps track of how many requests have come Into it over the course of its life span. We will then use a custom metric probe, and the PMX API to expose that information.

Create, if you haven't already, a bootstrap.js file and add the following to it :

Bootstrap.js walk through

In our bootstrap.js we setup a few things for our app. First we do the normal requires just to get the express app up and running. On line 3 however we import the pmx library and configure it. There are a few options that are boolean flags

• http - HTTP routes logging (default: false)Enable pm2 to perform http watching for http related metrics
  
• errors - Exceptions logging
• custom_probes - Auto expose JS Loop Latency and HTTP req/s as custom metrics
• network - Network monitoring at the application levelEnable calculation of lower level network statistics
  
• ports - Shows which ports your app is listening on
  

There are a lot more options that the pmx interface can be configured with which can be found here , for now however these are the ones we need to ensure are setup for this example. The following is the rest of the steps taken in our bootstrap.js file

• Then we pull in our metric middleware which we will go over in just a bit. 
• Then we insert that middleware into the Express app request life cycle so it can intercept all requests that come into our app. 
• Then we add a health check route so we can check to see if our app is running, but also it's a simple route that we can hit to trigger our metric. 
• Then we start our server and output a success message for us to see in the console.

countMetric.js

In our bootstrap.js we pulled in a countMetric.js , if you haven't created that file, do so now. Then add the following to it :

While this file is long or complex it does act as a glue layer between your probe definitions from PMX to the your actual applications use of the metrics. This will allow you to change out metric calculation, implementation, or even library in the future without breaking your entire Express request life cycle. In this file we do the following :

• Pull in a countProbe - Will be covered next.
• Create a module export function that is pretty standard
• We tell our metric that we want to increment it's count by 1.
• Then we tell the life cycle it can continue with next()

count.js

count.js is a wrapper for the actual PMX probe creation that then gets exported. Again it's not complex or long, but breaking your modules out like this will prevent a lot of pain down the line when these metrics inevitably change. If you haven't already create this file, do so and add the following to it :

This will do the following for us :

• Pull in the PMX module
• Instantiate a new probe definition within PMX for us
• Export a defined probe type

PMX provides various metric types, not just counts. In this example we are only using count because it's simple and doesn't require high volumes of requests to show it working. PMX supports the following metric types all of which expose different methods once their type is defined by calling that metric type method on a new probe instance.

• Simple metrics: Values that can be read instantly
  • eg. Monitor variable value
• Counter: Things that increment or decrement
  • eg. Downloads being processed, user connected
• Meter: Things that are measured as events / interval
  • eg. Request per minute for a http server
• Histogram: Keeps a resevoir of statistically relevant values biased towards the last 5 minutes to explore their distribution
• eg. Monitor the mean of execution of a query into database

In our instance we are creating a counter type metric probe that we are simple adding to which expose the inc() and dec() methods that increments and decrements the count of the metric probe respectively. The agg_type param is optionnal, it can be sum, max, min, avg (default) or none. It will impact the way the probe data is aggregated within the Keymetrics/PMX report backend. Use none if this is irrelevant (eg: constant or string value).

Starting Our Project

Right, it's been a bit of a long winded explanation but we are finally there. Lets run our project, issue a npm start in your project directory. You should see something similar to this in your terminal :

Confirming it all works

If nothing errored out, then your little application is now running! You can now check your custom metric status by hitting the PMX metric report API by going to : localhost:9615 

I highly suggest you have a JSON parsing extension setup for your browser because it will give you way more information then you thought you ever needed for you instances. The pieces of this massive metrics dump that we are interested however are under the following JSON path : processes[].pm2_env.axm_monitor

Under that path you will find in the axm_monitor object there is a field name "Request Count" which is the name that was gave our counter probe in count.js , that is our custom metric value. Now to test it out you can go to localhost:3000/health , let that load. Now reload your metrics url, go back the same path and take note that the "value" property has been increased by 1. 

Conclusion

There is a lot of things you can get PM2 and PMX to do for you in the world of reporting, metrics and monitoring. This article hasn't even scratched the surface of what all can be done but hopefully it has peaked your interest enough to have you learn more about what you can do with PM2 to make managing your applications and services easier in everyday dev life.

If you want to poke around more feel free to download the sample code and mess around with all that PM2 and PMX has to offer. In addition I will link to all the resources that I used to create my first metrics and everything that was pulled into this article.

Links

https://expressjs.com/en/starter/hello-world.html

https://github.com/keymetrics/pmx

https://github.com/Unitech/pm2