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Run JAX-RS applications on Fn using JRestless
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Fn Project JRestless Blogging Example

Author: Rae Jeffries-Harris

This is an example JAX-RS app that can be deployed on the Fn platform.


JRestless allows you to create FaaS applications using JAX-RS. We are adding support for using JRestless on Fn.

This means you can use all the JAX-RS features you're used to, @Path, @GET, @QueryParam - all the marshalling and content-types, all the routing. All of it, in a FaaS function. JRestless uses Jersey internally so you have the full capability of the reference JAX-RS implementation.

If you take advantage of FnProject's Hot Functions you can build a responsive application which only runs when it's needed.

This project is an example of how to use JRestless build a JAX-RS app on FnProject.

How does it work?

The code in is a JAX-RS app:

  • - defines the routes
  • - POJO domain object
  • - Database connection code
  • - 5 lines of code to point JRestless at our app

Check out the code, then in the root of the project run:

$ fn build


Function raej/jrest:0.0.4 built successfully.

Make sure you have an fn server running (See the tutorial - TL;DR fn start)

Then create your app:

$ fn apps create jaxrs
Successfully created app:  jaxrs

$ fn deploy --app jaxrs --local

You will need a database, easy way is to run the ./ included in the repo.

Some config for your app:

## The IP address of the host from inside a container
$ export DOCKER_HOST_IP=$(docker inspect --type container -f '{{.NetworkSettings.Gateway}}' fnserver)

fn apps config set jaxrs DB_URL "jdbc:mysql://${DOCKER_HOST_IP}/POSTS"
fn apps config set jaxrs DB_DRIVER com.mysql.jdbc.Driver
fn apps config set jaxrs DB_USER jaxrs
fn apps config set jaxrs DB_PASSWORD SgRoV3s

Map the routes used by the app to the function: (use whichever image version was published in the previous deploy )

fn routes create jaxrs /route/html --image raej/jrest:0.0.2
fn routes create jaxrs /route/blogs --image raej/jrest:0.0.2
# fn routes create jaxrs /route/add  <-- this was added by `fn deploy` earlier

All 3 of these routes will point to the same container image.

Bask in the glory of your creation

Browse to http://localhost:8080/r/jaxrs/route/html to see the blog's UI.

There is a simple HTML page served from /html, which fetches data from /blogs and posts new blog entries to /add.

FAQ / Notes

QUESTION: How many Function containers will be used?

Fn treats each route independently, so there will be at least one per endpoint that you use. There may be more than one, as container instances will be created dynamically to cope with high load.

QUESTION: What about binding variables from path params?

Fn currently does not support wildcards in routes. Issues #170 and #256 track current proposals to fix this.

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