Getting Started with ‘docker’

Bhaskar V. Karambelkar

2017-07-14

The docker R package provides access to the docker API to programmatically control a docker engine from R. The docker engine could be running either locally or remotely. The docker package uses the reticulate R package to invoke the Python SDK for docker. Using the Python SDK allows the docker package to have a very minimal foot-print and yet allow complete docker API access. The package has been tested against docker engine running on Linux and Microsoft Windows and should also work under MacOS.

Controlling a docker engine from withing R can be useful for …

Installation

Release version

install.packages('docker')

OR development version

if(!require(devtools)) {
  install.packages("devtools")
}
devtools::install_github('user001vk/docker')

Setup

Before you can use this package you need to have Python 2.x (>=2.7) or Python 3.x (>=3.4) with the docker Python module which provides Python SDK for docker. A simple way to do this is using a virtual environment. virtualenvwrapper makes setting up Python modules quite painless.

Once you have installed Python and setup virtualenvwrapper you need to create a new virtual environment and install the docker Python module in it.

mkvirtualenv --python=/usr/bin/python3 docker
workon docker
pip install docker

# Test the SDK againsts a locally running docker
# You should have a locally running docker engine for this.
python -c 'import docker; print(docker.from_env().version())'

You should see something like below, provided you had a locally running docker engine.

{'Os': 'linux', 'Arch': 'amd64', 'KernelVersion': '4.10.0-24-generic', 'GitCommit': '02c1d87',
'Version': '17.06.0-ce', 'BuildTime': '2017-06-23T21:19:04.990631145+00:00',
'MinAPIVersion': '1.12', 'GoVersion': 'go1.8.3', 'ApiVersion': '1.30'}

Examples

Hello World!

Here we provide a simple getting started example. We start the alpine docker image which is a small Linux image.We run a command to output “Hello World!” from within the started docker container and access it on the R side.

# This is a hint to the reticulate package to find a
# python environment with the "docker" python module available.
reticulate::use_virtualenv("docker")
library(docker)
client <- docker$from_env()
s <- client$containers$run("alpine", 'echo -n "Hello World!"', remove=TRUE)
print(s$decode("UTF-8"))
[1] Hello World!

Real-World Example

Below is more of a real-world example where we start a redis container and interact with it using the rredis package, and subsequently tear it down.

reticulate::py_discover_config("docker")
library(docker)
library(rredis)

docker_client <- docker$from_env()
docker_client$ping()

redis_instance <- docker_client$containers$run(
  'redis', name='redis', detach=TRUE, ports=list('6379/tcp'='6379'))
redis_instance$status

redisConnect(host='127.0.0.1', port=6379, nodelay=TRUE)
redisSet('docker-test', rnorm(20))
redisGet('docker-test')

redis_instance$stop()
redis_instance$remove()

And here’s how it looks when run.

> reticulate::py_discover_config("docker")
python:         /home/user001/.virtualenvs/docker/bin/python
libpython:      /usr/lib/python3.5/config-3.5m-x86_64-linux-gnu/libpython3.5.so
pythonhome:     /usr:/usr
virtualenv:     /home/user001/.virtualenvs/docker/bin/activate_this.py
version:        3.5.2 (default, Nov 17 2016, 17:05:23)  [GCC 5.4.0 20160609]
numpy:          /home/user001/.virtualenvs/docker/lib/python3.5/site-packages/numpy
numpy_version:  1.13.1
docker:         /home/user001/.virtualenvs/docker/lib/python3.5/site-packages/docker

python versions found: 
 /home/user001/.virtualenvs/docker/bin/python
 /usr/bin/python
 /usr/bin/python3

> library(docker)

> library(rredis)

> docker_client <- docker$from_env()

> docker_client$ping()
[1] TRUE

> redis_instance <- docker_client$containers$run(
   'redis', name='redis', detach=TRUE, ports=list('6379/tcp'='6379'))

> redis_instance$status
[1] "created"

> Sys.sleep(5) # Wait for the container to start the service.

> redisConnect(host='127.0.0.1', port=6379, nodelay=TRUE)

> redisSet('docker-test', rnorm(20))
[1] "OK"

> redisGet('docker-test')
 [1]  1.01545119  0.08353996  0.71668645 -0.34256345 -0.09871241  0.24834106
 [7]  0.28802550  0.02321578 -1.62448884 -1.31099073  0.54530365  1.29799034
[13]  0.80973704  0.30018833 -0.72609402 -0.47678730 -0.79877246  1.08857741
[19] -1.92010832  1.61439356

> redis_instance$stop()
> redis_instance$remove()

The reticulate::py_discover_config("docker") call is used to ensure that reticulate was able to find a Python environment with the docker Python module installed.

Other Docker APIs

You can call every API supported by the Python SDK using reticulate. Please consult the documents for the SDK and the reticulate R package in the links given above.