Orbiter an OSS Docker Swarm Autoscaler

22 Apr 2017 · Seven minute read · on Gianluca's blog

My presentation at the Docker HQ in San Francisco.


One of the Cloud’s dreams is a nice world when everything magically happen. You have unlimited resources and you are just going to use what you need and to pay to you use. To do what AWS provides a service called autoscaling-group for example. You can specify some limitation and some expectation about a group of servers and AWS is matching your expectation for you. If you are able to make an automatic provision of a node you can use Cloudwatch to set some alerts. When AWS trigger these alerts the austocaling-group is creating or removing one or more instance.

let’s try with an example

You have a web service and you know that for 2 hours every day you don’t need 4 EC2 because you have a lot of traffic, you need 10 of them. You can create an autoscaling group, set some alerts:

  1. When the memory usage is more than 65% for 3 minutes start 3 new servers.
  2. When the memory usage is less than 30% for 5 minutes stop 2 servers.

Just to have an idea. In this way AWS knows what do you and you don’t need to stay in front of your laptop to wait something happen. You can just do something funny.

It’s something useful, if you think about a daily magazine, they usually has a lot of traffic in the beginning of the day when all the people are usually reading news. At that’s an easy scenario.

But it can also happen than a new shared on reddit or HackerNews is getting a lot of traffic and the last thing that you are looking for is to go down just during that spike!


There are different actors in this comedy. First of all our cluster needs to be manageable by outside via API. In this example I am going to use Docker Swarm, Orbiter supports a basic implementation for DigitalOcean but it still requires some toning.

You need to have some time series database or analytics platform that can trigger webhook to trigger orbiter based on some metrics.

We ran a demo with the TICKStack (InfluxDB, Telegraf, and Kapacitor) days ago. It’s available at this link.

In the end you need to deploy orbiter.

Orbiter, design and arch

Orbiter is an open source tool designed to be a cross platform autoscaler. It is in go and it provides a REST API to handle scale requests.

It provides one entrypoint:

curl -v -d '{"direction": true}' \

infra_scale for example contains information about the cluster manager, where it is, what is it? Docker or Digitalocean or what ever?

The policy describes how an application scale. If you know a bit Docker Swarm docker is the name of the service.

Orbiter supports two different boot methods. One is via configuration:

    provider: swarm
        up: 4
        down: 3

The second one is actually only supported by Docker Swarm and it’s called autodetection. In practice when you start orbiter, it’s looking for a Docker Swarm up and running. If it finds Swarm it’s going to list all the services deployed and it’s going to manage all the services labeled with orbiter=true.

By default up and down are set to 1 but you can override them with the label orbiter.up=3 and orbiter.down=2.

Let’s suppose to have a Docker Swarm cluster with 3 nodes.

$ docker node ls
11btq767ecqhelidu8ah1osfp *  node1     Ready   Active        Leader
ptre8d4bjccqi6ml6z445u0mz    node2     Ready   Active
q5rwi3cej9gc1vqyscwfau640    node3     Ready   Active

I deployed a service called gianarb/micro. It is an open source demo application. There are different versions, I deployed the version 1.0.0. It only shows the current IP of the container/server.

docker service create --label orbiter=true \
    --name micro --replicas 3 \
    -p 8080:8000 gianarb/micro:1.0.0

You can check the number of tasks running with the command:

$ docker service ps micro
ID                  NAME                IMAGE                 NODE
         onsqgriv3nel        micro.1             gianarb/micro:1.0.0   node3
         Running             Running 51 seconds ago

         yxtxyder7bs3        micro.2             gianarb/micro:1.0.0   node1
         Running             Running 51 seconds ago

         lyzxxdc00052        micro.3             gianarb/micro:1.0.0   node2
         Running             Running 52 seconds ago

At this point you can visit port 8080 of your cluster to have a look of the service but for this demo doesn’t really matter. We are going to start orbiter and we are going to trigger a scaling policy to simulate a request made by our monitoring tool.

docker service create --name orbiter \
    --mount type=bind,source=/var/run/docker.sock,destination=/var/run/docker.sock \
    -p 8000:8000 --constraint node.role==manager \
    -e DOCKER_HOST=unix:///var/run/docker.sock \
    gianarb/orbiter daemon --debug

I am using Docker to deploy orbiter as service. I am using the Unix Socket to communicate with Docker Swarm and I am deploying this service into the manager because it needs to have write permission to start and stop tasks. This can be done only into the manager. You can configure orbiter with the variable DOCKER_HOST to use REST API. In this way you don’t have this constraint. This configuration in very easy to show in a demo like this one.

$ docker service logs orbiter
orbiter.1.zop1qkwa1qxy@node1    | time="2017-04-18T09:24:56Z" level=info
msg="orbiter started"
orbiter.1.zop1qkwa1qxy@node1    | time="2017-04-18T09:24:56Z" level=debug
msg="Daemon started in debug mode"
orbiter.1.zop1qkwa1qxy@node1    | time="2017-04-18T09:24:56Z" level=info
msg="Starting in auto-detection mode."
orbiter.1.zop1qkwa1qxy@node1    | time="2017-04-18T09:24:56Z" level=info
msg="Successfully connected to a Docker daemon"
orbiter.1.zop1qkwa1qxy@node1    | time="2017-04-18T09:24:56Z" level=debug
msg="autodetect_swarm/micro added to orbiter. UP 1, DOWN 1"
orbiter.1.zop1qkwa1qxy@node1    | time="2017-04-18T09:24:56Z" level=info
msg="API Server run on port :8000"

As you can see into the logs the API are running on port 8000 and orbiter already detected a service called micro, the one that we deployed before and it auto-created a autoscaling group called autodetection_swarm/micro. This is the unique name that we can use when we trigger our scale request.

$ curl -d '{"direction": true}' -v
*   Trying
* Connected to ( port 8000 (#0)
> POST /handle/autodetect_swarm/micro HTTP/1.1
> Host:
> User-Agent: curl/7.52.1
> Accept: */*
> Content-Length: 19
> Content-Type: application/x-www-form-urlencoded
* upload completely sent off: 19 out of 19 bytes
< HTTP/1.1 200 OK
< Content-Type: application/json
< Date: Tue, 18 Apr 2017 09:30:35 GMT
< Content-Length: 0
* Curl_http_done: called premature == 0
* Connection #0 to host left intact

With that cURL I simulated a scale request and as you can see in the log above orbiter detected the request and it scaled up 1 task for our service called macro

$ docker service logs orbiter
orbiter.1.zop1qkwa1qxy@node1    | POST /handle/autodetect_swarm/micro HTTP/1.1
orbiter.1.zop1qkwa1qxy@node1    | Host:
orbiter.1.zop1qkwa1qxy@node1    | Accept: */*
orbiter.1.zop1qkwa1qxy@node1    | Content-Length: 19
orbiter.1.zop1qkwa1qxy@node1    | Content-Type:
orbiter.1.zop1qkwa1qxy@node1    | User-Agent: curl/7.52.1
orbiter.1.zop1qkwa1qxy@node1    |
orbiter.1.zop1qkwa1qxy@node1    | {"direction": true}
orbiter.1.zop1qkwa1qxy@node1    | time="2017-04-18T09:30:35Z" level=info
msg="Received a new request to scale up micro with 1 task." direc
tion=true service=micro
orbiter.1.zop1qkwa1qxy@node1    | time="2017-04-18T09:30:35Z" level=debug
msg="Service micro scaled from 3 to 4" provider=swarm
orbiter.1.zop1qkwa1qxy@node1    | time="2017-04-18T09:30:35Z" level=info
msg="Service micro scaled up." direction=true service=micro

We can verify the current number of tasks that are running for micro and we can see that it’s not 3 as before but 4.

$ docker service ls
ID                  NAME                MODE                REPLICAS
azi8zyeor5eb        micro               replicated          4/4
ezklgb6uak8b        orbiter             replicated          1/1

This project is open source on github.com/gianarb/orbiter you can have a look on it, try and leave some feedback or request if you need something different.

PR are also open if you are working with a different cluster manager or with a different provider, add a new one is very easy. It’s just a new interface to implement.

Something weird with this website? Let me know.