dockerode – Not another Node.js module

While developing I looked for Node.js modules that implemented the Remote API.

I found a few, the majority was  unfinished lacking a lot of functionality and tests.

Things I was looking for:

  • Complete feature set
  • Tests
  • Leverage streams
  • Good abstraction

I didn’t found a module with these characteristics or with a code base ready to accept contributions.

At the time I ended up forking fixed some bugs it had (this module was revamped recently and it’s better now) and implemented some functionality I needed. But all this was really quick patch, I knew that someday I had to do something about this.

That day came yesterday, and another node.js module was born… it’s main objectives are those four points I enumerated in this post.

I called it dockerode (docker+node yes naming stuff isn’t a skill I’m proud of…)

How it works and what it can do


var Docker = require('dockerode');
var docker = new Docker({socketPath: '/var/run/docker.sock'});
var docker2 = new Docker({host: '', port: 3000});

By leveraging streams it allows to do cool stuff like:

container.attach({stream: true, stdout: true, stderr: true}, function(err, stream) {

Containers and images are entities:

docker.createContainer({Image: 'ubuntu', Cmd: ['/bin/bash']}, function(err, container) {
  container.start(function(err, data) {

var container = docker.getContainer('71501a8ab0f8');
container.inspect(function(err, data) {


“docker run” implementation:

//, cmd, stream, temporary, callback)'ubuntu', 'uname -a', process.stdout, true, function(err, data) {

Installation and tests

npm install dockerode

Tests use mocha and chai.js


  • Feature set is almost complete, tests are about 85%.
  • New WebSockets endpoints added in Docker v0.6 will be supported soon.


Nodechecker is an app I built a few weeks ago that automatically tests all node.js modules available in the NPM registry. Check these slides from require(‘lx’) for more details, they explain the idea and motivation behind Nodechecker but the technical stuff is now outdated as you will see in this post.

It all started with a PoC around node.js and, it worked well for the NPM use case but it didn’t scale for other use cases like on demand testing.

Nodechecker new architecture

Nodechecker new architecture

This is the new architecture, it relies on multiple Docker instances completely abstracted each one running nodechecker-engine, I call this entity worker nodes.

The beautiful thing about this is, that I can add more worker nodes without even rebooting/restarting anything. Just boot another VM with Docker already installed and run nodechecker-engine specifying the nodechecker-balancer‘s ip address in the argument.

When the engine starts it will make a dnode call to nodechecker-balancer basically saying “i’m here and ready to rock please add me to the available worker nodes list

Nodechecker-balancer always dispatches work to the node that have the smallest work queue, if you add new nodes they will probably be the ones getting new work orders.

This architecture is so agile that if you just want to fiddle a little with it you don’t need to run a balancer, just run a single worker node without specifying an ip address in it’s nodechecker-engine. Then in the nodechecker-crawler and api just use the worker ip address.

You may even run crawler, api and balancer and even a worker inside a single machine 🙂

Everything is still in a rough state, feel free to contribute.

Binary encoding deprecation in Node.js

Recently I had to implement an endpoint for an archaic API in Node.js, which required some binary manipulation.

Giving a quick peak at documentation, you will see that binary encoding should be avoided at all costs and is already deprecated, instead you should rely on buffers.

Here goes a really basic and quick example doing the same thing using encoding and then using buffers.

What you should NOT be doing:

stream.write(utils.pack('N', + 4) +,
 'binary', payload.callback);

Instead you should be doing:

var myb = new Buffer( + 4);
myb.writeUInt32BE(( + 4), 0);
myb.write(, 4);
stream.write(myb, payload.callback);

Realize that when you use a buffer in the write method, encoding does not fallback to utf8 by default.

Rebuilding Outkept

Outkept DashboardLast November I did a talk at Codebits about a private project that ended to be Outkept, it was basically a project that was build for a  specific use case and then I generalized it.

At the time I developed it in Java, but after the talk I decided to rebuild it for more generalist use cases and start everything entirely from scratch in node.js.

Outkept allows you to control and monitor a large server cluster, without needing to manually specify which and what servers to monitor/control. Instead you just define which subnets you want to control and then, using SSH, Outkept‘s crawlers will look for servers and what do they support.

Rebuilding it in node.js was awesome, allowing me to tackle my node.js skills and dig more into node’s scene while using a lot ‘earlier adopter’ tech.

Right now Outkept v2 supports everything the old version supported and even more, things are quicker and more fluid. New dashboard connects using shoe (sockjs) and the new system relies entirely in multiple node.js processes.

I will talk more about this project later, but right now I would love some feedback. The codebase is big and mostly uncommented, in the next posts will fix this and talk a bit about it.

If you want to give it a try just follow these instructions. If you need help you can reach me at

Disrupting Java apprentices with node.js

I started lecturing a few years ago, for a while it was a fulltime job. I lectured mainly in two programming languages: C in introductory classes (first semester) and Java for OOP, data structures and distributed systems classes (equally distributed along the bachelor degree).

After a while I got bored and nowadays being a lecturer is not a fulltime job, my main contribution now is to bring fresh tech into the play and introduce it to seniors and other lecturers and this is where this story starts.


About one year ago I started diving into node.js. Initially I only used it for non critical stuff, still using Java as my main language.
I really liked node from the first day but I just didn’t have the time to dive into it at the time.
About 6 months ago everything changed, I’m really hooked into it and now I finally feel that I acquired enough skill to allow it to replace Java in my head.
Node ecosystem is awesome and it doesn’t have all that clutter that Java has, it is so clean and agile…

This semester I decided to bring node.js into a senior class and simultaneously a few senior projects.

Remember how I started this post?

In here almost every design/programming topics are taught Java, when I gave the first class about JavaScript and node.js everyone was like “WTF”?
A few students even looked at me thinking I was drunk because in their heads Javascript was for browsers and nothing else.

In order to sell them node.js I live coded a drag-n-drop DIV element that moved simultaneously in all browsers using Instantly everyone on the room was curious about this, even the more sceptic ones. (if you want to disrupt someone show them something very graphic/explicit and that I did)
Code available at (it uses prototype based objects, modules, and events)

It’s true that I could have implemented that in almost any other language, but the lack effort needed to implement it in node.js is really impressive and that was what disrupted the audience (npm awesomeness helped :-D).

Right now seniors are starting to put their hands on node.js at multiple projects ( – Portugol rewritten in node.js) so far I feel that the hardest thing for them is the asynchronous architecture.

Although one big advantage I felt was the fact that they came from a language where everything is an Object (Java), because of this they quickly understood objects in JavaScript and how can events be used for message passing in an asynchronous environment.

In my opinion this is one of the most important thing to understand in the Javascript/node.js world.