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Running Microservices in OSv

This repository serves demonstration purposes of the improvements made to OSv and Capstan in the MIKELANGELO project. OSv is a operating system designed specifically for lightweight cloud workloads. It's been developed initially by Cloudius Systems, now ScyllaDB. Capstan is a tool for rapidly composing applications into self-contained virtual machines ready to be deployed to various virtual machine monitors.

The design for this demo is based on a tutorial written by Jacob Martin. The microservices are implemented in JavaScript using Node.js runtime.

Application Services

The application consists of five specialised microservices, each responsible for its own task. The application allows users to upload photos, which are processes using a static image filter and stored for users to download them after being processed. The RESTful API is intentionally kept at a minimum.

These services are

  • keyvaluestore.js: a central key-value store which is used by other services to register themselves and to query information about other services in the deployed system
  • db.js: a simple database service storing information about the tasks to be handled by the workers
  • storage.js: file storage used to save images to be processed by the system
  • master.js: master service through which most of the other services operate
  • worker.js: executor who is processing pending tasks by acquiring the image from the storage, transforming it and saving it back to the storage

Application Workflow

The workflow consists of two phases. During the first phase, the microservices are registered in the key-value storage. Each service will register its access point (e.g. http://hostname:port) from where other services will be able to look it up.

Initialisation phase

Once the services are registered, the application can be used. The collaboration between the services is depicted in the following diagram. This diagram introduces a frontend which is not part of this repository (it could be a web app using the backend API or just a simple curl).

Worker phase

Using the Application

Before you can use the application, ensure you have Node.js installed (version 4.4.5 was used for this tutorial). Navigate to the root directory of this project and install required packages

$ npm install

This will download and install required packages inside node_modules subdirectory. You should now be able to launch individual services. Start with the central key-value store:

$ node keyvaluestore.js
server is listening on 8000

In separate terminals launch remaining services:

$ node db.js localhost:8000
Database endpoint registered
Database is listening on 8001
$ node storage.js localhost:8000
Storage endpoint registered
Storage is listening on 8002
$ node master.js localhost:8000
Master endpoint registered
Master is listening on 8003

If done correctly, the key-value store should provide information about registered servives, e.g.:


If not, open an issue :-).

Now try and upload one photo using the master node (check the above diagram to understand why we are uploading photos to the master service).

$ curl -X POST -F "image=@/path/to/photo.png" http://$MASTER_ENDPOINT/task

Now launch the worker:

$ node worker.js localhost:8000
Working on task 2
        processing /home/lemmy/dev/mpm/node-micri/worker/2.png
Nothing to do at the moment

To upload more photos at the same time, you can use the accompanied script bin/

$ ./bin/ localhost:8000 /home/lemmy/dl/IMG_0995.PNG 20

This will

  • query the key-value store at localhost:8000 to get the endpoint of the master
  • upload the phoot at given path /home/lemmy/dl/IMG_0995.PNG 20 times

Now start your worker again

$ node worker.js localhost:8000
Working on task 3
        processing /home/lemmy/dev/mpm/node-micri/worker/3.png
Working on task 4
        processing /home/lemmy/dev/mpm/node-micri/worker/4.png
Working on task 5
        processing /home/lemmy/dev/mpm/node-micri/worker/5.png
Working on task 6

You can start as many workers are necessary. In case a task is not finished by a certain timeout, another worker will try to process it again. This allows you to stop the workers without fearing to loose or miss a task. Feel free to upload new and new photos to the app.

Here Come Unikernels

This project already contains Capstan package descriptor. Before you can use it, you should follow these instructions to get capstan tool.

The package manifest is described in meta/package.yaml file:

name: node-micro
title: Node Microservices
author: lemmy

name, title and author are used by Capstan mainly for displaying this information at various places. The require lists all packages that need to be collected while composing target unikernel (target VM comprised of bootloader, OSv kerenel and your application). To get a list of packages available for download, use capstan package search command. When looking for a specific package, add the name, for example

$ capstan package search node
Name                                               Description                                        Version                   Created              NodeJS-4.4.5                                       4.4.5                     0001-01-01T00:00:00Z              NodeJS                                             v0.24-300-g33e3a36        0001-01-01T00:00:00Z              NodeJS-4.4.5                                       4.4.5                     0001-01-01T00:00:00Z

Then just add the package name to the list of required packages. For example, if you'd like to add the CLI (Command Line Interface, a simple shell in OSv), add eu.mikelangelo-project.osv.cli to the list of required packages (to get the full name, we used capstan package search cli).

Now that we have the basics covered (feel free to read through the documentation of Capstan project) we can continue preparing the unikernel. Let's compose the virtual machine image:

$ capstan package compose node-micro/tutorial
Empty command line will be set for this image
Importing node-micro/tutorial...
Importing into /home/lemmy/.capstan/repository/node-micro/tutorial/tutorial.qemu
Uploading files to /home/lemmy/.capstan/repository/node-micro/tutorial/tutorial.qemu...
Setting cmdline: --norandom --nomount --noinit /tools/; /tools/ --prefix /zfs/zfs; / set compression=off osv
Uploading files 3016 / 3016 [=========================================================] 100.00 % 4s
All files uploaded
Command line set to: ''

That's it. You now have a complete Node.js application ready to be executed inside lightweight virtual machine based on OSv. Check this out:

$ qemu-img info /home/lemmy/.capstan/repository/node-micro/tutorial/tutorial.qemu
image: /home/lemmy/.capstan/repository/node-micro/tutorial/tutorial.qemu
file format: qcow2
virtual size: 10G (10737418240 bytes)
disk size: 33M
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false
    refcount bits: 16
    corrupt: false

Notice the disk size? That's all it takes to host a self-contained Node.js app inside OSv.

The Capstan tool is used to launch individual unikernels. The simplest way to start this image is to use the following command:

$ capstan run -e "/node keyvaluestore.js" node-micro/tutorial
Created instance: node-micro-tutorial
Setting cmdline: /node keyvaluestore.js
OSv v0.24-300-g33e3a36
server is listening on 8000

This will use default values for various configuration options, launch a VM using QEMU/KVM hypervisor and start the application.

To be more useful in a local environment, we are going to use the following command:

$ sudo ~/dev/bin/capstan run -m 200M -c 1 -n vhost --mac="A2:13:15:00:80:01" -e "/node keyvaluestore.js" -i node-micro/tutorial node-micro-keyvaluestore

First note that the actual command to start the service as an OSv VM is quite the same as before /node keyvaluestore.js. The other parts of the above command are explained next:

  • sudo: only needed because we are using vhost networking
  • ~/dev/bin/capstan: location of the capstan tool
  • -m 200M: the VM should only get 200 MB of RAM
  • -c 1: one virtual CPU
  • -n vhost: use vhost networking (check the QEMU network configuration when this mode is enabled)
  • --mac="A2:13:15:00:80:01": specify a fixed MAC address so that we get the same IP on successive launches
  • -e "/node keyvaluestore.js": the actual command we'd like to launch
  • -i node-micro/tutorial: the image to use when launcing this VM (it should be the same as it was used in the capstan package compose command above)
  • node-micro-keyvaluestore: name of the instance

Once the VM is created, output like the one below should be seen

Created instance: node-micro-keyvaluestore
Setting cmdline: /node keyvaluestore.js
OSv v0.24-300-g33e3a36
server is listening on 8000

This means that the key-value store is accessible at Now we are ready to start all other services (in separate terminals):

Database Service:

$ sudo ~/dev/bin/capstan run -c 1 -n vhost --mac="A2:13:15:00:80:02" -e "/node db.js" -i node-micro/common node-micro-db
Created instance: node-micro-db
Setting cmdline: /node db.js
OSv v0.24-300-g33e3a36
Database endpoint registered
Database is listening on 8001

Storage Service:

$ sudo ~/dev/bin/capstan run -c 1 -n vhost --mac="A2:13:15:00:80:03" -e "/node storage.js" -i node-micro/common node-micro-storage
Created instance: node-micro-storage
Setting cmdline: /node storage.js
OSv v0.24-300-g33e3a36
Storage endpoint registered
Storage is listening on 8002

Master Service

$ sudo ~/dev/bin/capstan run -c 1 -n vhost --mac="A2:13:15:00:80:04" -e "/node master.js" -i node-micro/common node-micro-master
Created instance: node-micro-master
Setting cmdline: /node master.js
OSv v0.24-300-g33e3a36
Master endpoint registered
Master is listening on 8003

All set! Let's upload a photo:

$ ./bin/ /home/lemmy/dl/mike-team.png
Uploading to

And now, start your worker:

$ sudo ~/dev/bin/capstan run -c 1 -n vhost -e '/node worker.js' -i node-micro/tutorial node-micro-worker1
Created instance: node-micro-worker1
Setting cmdline: /node worker.js
OSv v0.24-300-g33e3a36
Working on task 0
        processing //worker/0.png
Nothing to do at the moment

Start new workers, upload new photos, stop workers, stop services, play and enjoy :-).

Updating Virtual Machine Image

When you change your scripts, you can simply recompose the image using the same command as above:

$ capstan package compose node-micro/tutorial

However, this will rebuild entire VM, which means that besides your own scripts, it will upload all dependent NPM modules from node_modules, Node runtime itself, etc. To speedup incremental VM builds, --update flag can be passed to Capstan. This will cause Capstan to check for changes and only update those files that were actually changed:

$ capstan package compose --update node-micro/tutorial

Deploying Unikernels on Kubernetes

You can deploy osv-microservice-demo application on Kubernetes with ease. If you don't have a working Kubernetes cluster up-and-running with Virtlet plugin installed, please follow instructions from here. Below please find steps that we took to setup such environment on Ubuntu 16.04 machine.

Setup local Kubernetes/Virtlet cluster on Ubuntu 16.04

Install Docker engine and kubectl client program that will be used to manage Kubernetes cluster:

$ curl -s | apt-key add -
$ sudo cat <<EOF >/etc/apt/sources.list.d/kubernetes.list
deb kubernetes-xenial main
$ apt-get update
$ apt-get install -y kubectl docker-engine
$ sudo usermod -aG docker $(whoami) # log-out and log-in afterwards

Configure and run fake Kubernetes cluster:

$ git clone
$ cd virtlet/deploy
$ ./
// takes a few minutes to complete

The script above takes quite some time since it sets up a whole DIND Kubernetes cluster on your local machine. When it finishes, you can (optionally) boot up Kubernetes GUI server:

$ kubectl proxy
# then visit http://localhost:8001/ui to browse Kubernetes UI

Test if everything works:

$ kubectl get pods --namespace kube-system
NAME                                    READY     STATUS    RESTARTS   AGE
etcd-kube-master                        1/1       Running   1          4h
image-server-1782580915-zv2w3           1/1       Running   0          4h
kube-apiserver-kube-master              1/1       Running   1          4h
kube-controller-manager-kube-master     1/1       Running   0          4h
kube-dns-3946503078-zplxw               3/3       Running   0          4h
kube-proxy-3r4p3                        1/1       Running   0          4h
kube-proxy-qck08                        1/1       Running   0          4h
kube-proxy-sw8rm                        1/1       Running   0          4h
kube-scheduler-kube-master              1/1       Running   1          4h
kubernetes-dashboard-2396447444-hn0jr   1/1       Running   0          4h
virtlet-8glgr                           1/1       Running   0          4h

Notice the image-server-1782580915-zv2w3 here since we will be uploading OSv images to it. The imageserver pod is nothing but an Nginx server serving unikernel images. We only use it to make those images accessible from withing Kubernetes network. If you have unikernel images accessible within some public server, then you won't need imageserver at all.

Deploy microservices

To deploy osv-microservice-demo application use the two yaml blueprints given in virtlet_deploy folder:

The former is responsible for microservices to be addressable by name (regardelss the actual IP), while the latter specifies what unikernels to deploy and how many. Go ahead, deploy application on Kubernetes cluster:

// Deploy k8s Service definitions for osv-microservice-demo
$ kubectl create -f ./virtlet_deploy/micro-services.yaml

// Deploy k8s Deployment definitions for osv-microservice-demo
$ kubectl create -f ./virtlet_deploy/micro-deployments.yaml

If you examine micro-deployments.yaml content you will notice that unikernel images are obtained from S3 object store. We've prepared these images for you using Capstan tool. Read this document to learn how to prepare them on your own.


If everything went OK you should see something like this on Kubernetes GUI at http://localhost:8001/ui (replace localhost with appropriate IP in case you're not running local cluster):

Kubernetes all green

If you prefer CLI:

$ kubectl get pods
NAME                                  READY     STATUS    RESTARTS   AGE
micro-db-2179323451-23zml             1/1       Running   0          6m
micro-keyvaluestore-147712366-b5sfl   1/1       Running   0          6m
micro-master-1491918165-wzwff         1/1       Running   0          6m
micro-storage-1856298744-zfvf9        1/1       Running   0          6m
micro-ui-280641514-rbl0k              1/1       Running   0          5m
micro-worker-1113504003-pkq8k         1/1       Running   0          6m
nginx-158599303-h2kxd                 1/1       Running   0          9m

Wooohoo, everything seems to be up-and-running! :D To start using application just query the micro-ui pod IP using Kubernetes dashboard:

Kubernetes UI IP

Or from CLI:

$ kubectl describe pod micro-ui-280641514-rbl0k | grep IP

There you go! Visit UI and start using osv-microservice-demo application! :)

Scale workers

If you need more workers to process your images, you just need to perform two clicks on the Kubernetes GUI:

Kubernetes scale up

Or from CLI:

$ kubectl scale deployment micro-worker --replicas=5
deployment "micro-worker" scaled

Getting help

Should you have any further questions, open an issue or ping us at @mikelangelo_eu.


This project has been conducted within the RIA MIKELANGELO project (no. 645402), started in January 2015, and co-funded by the European Commission under the H2020-ICT- 07-2014: Advanced Cloud Infrastructures and Services programme.


Simple Node.js Microservice application use to demonstrate the use of OSv and Capstan




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