Template for running Ruby/Sinatra microservices
Clone or download
nvdk release 2.10.0
This release moves the linkeddata gem from 2.0.0 to 3.0.1. See https://github.com/ruby-rdf/rdf/releases/tag/3.0.0 for more information
Latest commit 682d69b Aug 27, 2018
Type Name Latest commit message Commit time
Failed to load latest commit information.


Mu Ruby template

Template for running Ruby/Sinatra microservices

Using the template

Extend the semtech/mu-ruby-template and set a maintainer. That's it.

Configure your entrypoint through the environment variable APP_ENTRYPOINT (default: web.rb). You can use the Gemfile as you would expect.

Example Dockerfile

FROM semtech/mu-ruby-template:2.10.0
LABEL maintainer="erika.pauwels@gmail.com"
# ONBUILD of mu-ruby-template takes care of everything


The following versions of the mu-ruby-template are available:

  • 2.10.0; 2.10.0-ruby2.5
  • 2.9.0 ; 2.9.0-ruby2.5
  • 2.8.0 ; 2.8.0-ruby2.5
  • 2.7.0 ; 2.7.0-ruby2.5
  • 2.6.0 ; 2.6.0-ruby2.3
  • 1.3.1-ruby2.1


The template supports the following environment variables:

  • MU_SPARQL_ENDPOINT: SPARQL read endpoint URL. Default: http://database:8890/sparql (the triple store should be linked as database to the microservice).

  • MU_APPLICATION_GRAPH: configuration of the graph in the triple store the microservice will work in. Default: http://mu.semte.ch/application. The graph name can be used in the service via the graph helper method.

  • MU_SPARQL_TIMEOUT: timeout (in seconds) for SPARQL queries. Default: 60 seconds.

  • LOG_LEVEL: the level of logging (default: info, values: debug, info, warn, error, fatal).

Developing with the template

Livereload is enabled automatically when running in development mode. You can embed the template easily in a running mu.semte.ch stack by launching it in the docker-compose.yml with the correct links. If desired, pry and Better Errors can be used during development, giving advanced ruby debugging features.

Live reload

When developing, you can use the template image, mount the volume with your sources in /app and add a link to the database. Set the RACK_ENV environment variable to development. The service will live-reload on changes. You'll need to restart the container when you define additional dependencies in your Gemfile.

docker run --link virtuoso:database \
       -v `pwd`:/app \
       -p 8888:80 \
       -e RACK_ENV=development \
       --name my-js-test \

Develop in mu.semte.ch stack

When developing inside an existing mu.semte.ch stack, it is easiest to set the development mode and mount the sources directly. This makes it easy to setup links to the database and the dispatcher.

Optionally, you can publish the microservice on a different port, so you can access it directly without the dispatcher. In the example below, port 8888 is used to access the service directly. We set the path to our sources directly, ensuring we can develop the microservice in its original place.

  image: semtech/mu-ruby-template:2.10.0
    - 8888:80
    RACK_ENV: "development"
    - db:database
    - /absolute/path/to/your/sources/:/app/

Debugging with pry and Better Errors

Add a breakpoint in your code by inserting a binding.pry statement.

When an error occurs, an interactive Better Errors error page is available at http://{container-ip}/__better_errors. It's important to access the error page via the container's IP directly and not through localhost, identifier, dispatcher, etc.

Helper methods

The template provides the user with several helper methods in Sinatra. Some helpers cannot be used outside the Sinatra context.

error(title, status = 400)

Returns a JSONAPI compliant error response with the given status code (default: 400).


Returns the application graph configured through the MU_APPLICATION_GRAPH.


Generate a random UUID (String).


The parsed JSON body of the request.


The template provides a Logger log object to the user for logging. Just do log.info "Hello world". The log level can be set through the LOG_LEVEL environment variable (default: info, values: debug, info, warn, error, fatal).

Logs are written to the /logs directory and STDOUT in the docker container.


Executes the given SPARQL select/ask/construct query.


Get the rewrite URL from the request headers.


Get the session id from the request headers.


Returns a SPARQL::Client instance connection to the SPARQL endpoint configured through the MU_SPARQL_ENDPOINT environment variable.

sparql_escape ; sparql_escape_{string|uri|date|datetime|bool|int|float}(value)

The Ruby templates extends the core classes String, Date, DateTime, Time, Integer, Float, Boolean and URI with a sparql_escape method. This method can be used to avoid SPARQL injection by escaping user input while constructing a SPARQL query. E.g.

query =  " INSERT DATA {"
query += "   GRAPH <#{settings.graph}> {"
query += "     <#{user_uri}> a <#{RDF::Vocab::FOAF.Person}> ;"
query += "                   <#{RDF::Vocab::FOAF.name}> #{name.sparql_escape} ;"
query += "                   <#{RDF::Vocab::DC.created}> #{now.sparql_escape} ."
query += "   }"
query += " }"

Next to the extensions, the template also provides a helper function per datatype that takes any value as parameter. E.g. sparql_escape_uri("http://mu.semte.ch/application").


Executes the given SPARQL update query.

update_modified(subject, modified = DateTime.now)

Executes a SPARQL query to update the modification date of the given subject URI (string). The date defaults to now.


Validate whether the Content-Type header contains the JSONAPI Content-Type. Returns a 400 otherwise.

validate_resource_type(expected_type, data)

Validate whether the type specified in the JSON data is equal to the expected type. Returns a 409 otherwise.

Helpers outside the Sinatra context

The template provides several helpers that are automatically included in the Sinatra application (web.rb), but some of them can also be used outside the Sinatra context. Just include the SinatraTemplate::Utils module in your file.

require_relative '/usr/src/app/sinatra_template/utils.rb'
include SinatraTemplate::Utils

The following helper methods are provided:

  • graph
  • generate_uuid
  • log
  • query(query)
  • sparql_client
  • update(query)
  • update_modified(subject, modified = DateTime.now)

Writing tests for your microservice

To test your app, run the container with RACK_ENV set to test. All rspec tests matching *_spec.rb in spec/ and its subdirectories will be executed.

docker run --rm -e RACK_ENV=test microservice-image

To run the tests while developing, start an interactive container in the test enviroment with your code folder mounted in /app:

docker run --volume /path/to/your/code:/app
            -e RACK_ENV=test
            -it semtech/mu-ruby-template:2.10.0 /bin/bash

You can now run your tests inside the container with:

bundle install
rspec -c

Custom build commands

To execute custom bash statements during the image build (e.g. to install aditional system libraries), provide an on-build.sh script in the root of your service. It will be automatically picked up and executed by the Docker build.

Experimental features

MU_SPARQL_UPDATE_ENDPOINT environment variable

Configure the SPARQL update endpoint path. This should be a path relative to the base of MU_SPARQL_ENDPOINT. Default: /sparql. The update endpoint can be retrieved via the update_endpoint helper method.