The Flogo project. A simple REST example

The Tibco community has developed an ultralight Open Source Framework to develop Go microservices or, as they say, "event driven applications". Actually, the community edition, includes triggers which listen the following events: prompt commands (CLI triggers), timers, load testers, channels and HTTP messages.

Figure 1. The Flogo project.
Image from https://tibcosoftware.github.io/flogo/introduction/

In this tutorial, we’ll illustrate how to use Flogo to make POST requests sending JSON content which will trigger two request (actions) to other REST services.

Setting up the example

Requirements:  Docker (https://docs.docker.com)

First, let's go over a simple example. We have a blog service and will use Flogo to develop a POST method for the "posts" resource in order to add comments:

 POST  /posts/{postId}/addComment
{
  "body": "Lorem ipsum dolor sit amet, consectetur ...",
  "author": "alnura"
}

Our method will check that the post exists and, in that case, it will add the comment. Suppose that we already have a some resources which we will use in his example

 GET  /posts/{postID}

 POST  /comments
{
 "date": "2019-09-29T18:46:19Z",
 "body": "Lorem ipsum dolor sit amet, consectetur ...",
 "author": "alnura",
 "postId": 1
}

I will use json-server to implement this services using the following db.json:

{ "posts": [    { "id": 1, "body": "foo" },    { "id": 2, "body": "bar" }  ], "comments": [    { "id": 1,       "body": "baz",       "author": "alnura",       "postId": 1      }  ]}

Fetch the later json-server docker image and launch the server:

$ docker run -d -p 80:80 -v <my_path>/db.json:/data/db.json clue/json-server

You can build Flogo applications using Web UI or typing your flow definition json file and using the Flogo cli tool to build your executable file. In this post we will use Web UI so let's start by launching it:

$ docker run -it -p 3303:3303 flogo/flogo-docker:latest eula-accept

The WebUI connects to GitHub to build applications. Disable the SSL certificate checking to avoid connection problems:

$ docker exec <container ID> git config --global http.sslVerify false


Open your favorite web browser, and navigate to http://localhost:3303

Figure 2. Web UI welcome screen.

Create a new application

Click on the New button, set the name (my-blog).

Figure 3. Empty application.

Add a new action called posts.

Figure 4. Adding a new action.

Add a trigger

Click on the "Post" action and add a new trigger by clicking on the (+) icon on the left hand side of the screen and selecting  "Receive an HTTP message".

Now it is time to configure the trigger. To start, click on the trigger and a new dialog will open with a bunch of options. In this dialog you’ll have to provide:

• Port: 8081
• Method: POST
• Path: /posts/:postid/addComment

Save and close.

Note:
Each new action requires a different ports. Choose the "triggers view" if you want to add new methods to the "posts" resource.

Set the flow input and map trigger input to flow input

Click on the input/output icon and define input params.

Figure 5. Setting input/output data.

Save, close and click on the the trigger. Select the "Map to flow's input" tab and provide the following data:

• author:   $.content.author
• body:     $.content.body
• post_id:  $.pathParams.postid

Call "posts" REST service (GET request)

Let's check that the "postid" exist before adding a comment. It's a good practice to include log actions in your flows. I will include some in order to make this one clearer. Add a new "Log" action to the flow. Click on the "..." to activate/deactivate options and click in the  wheel to edit the action. Type the following message in the "Map input" tab:

message:   string.concat("Adding a comment to the post ", $flow.post_id

Add a REST invoke action.

Figura 6. Adding a new REST invoke action.

Edit the REST invoke action and insert the following data:

Settings tab

• method: GET
• uri: "http://localhost/posts/:id"

Map input tab

• pathParams:  {"id":"=$flow.post_id"

Call "comments" REST service (POST request)

Add a new REST invoke action next to the previous one.
Settings tab

method: POST
uri: "http://localhost/posts/:id"

Map input tab

content: {  "body": "=$flow.body",  "author": "=$flow.author",  "postId": "=$flow.post_id"}

Our application just return the http status, however you can customize the response by adding a Return activity and map inputs to outputs.

Build and run the application

Flogo command CLI allows you to build the application from the command line however I will show you how to build the application using the Web UI. Let's start a linux container (Ubuntu), where we will run the application.

$ docker run -v <your_home>/Downloads:/tmp --name ubuntu --network=my-net  -p:8081:8081 --rm -i -t ubuntu bash

Note that I used the Downloads folder as a mount point. WebUI download the executable generated to the user's downloads folder so change to the /tmp directory

$ root@ba300b47a479:/tmp#

Edit you application on the WebUI, click on the build button and select the Linux/arm64 target.

Figure 7. Building your application.

Once your application is downloaded, grant it execution permissions:

$ root@ba300b47a479:/tmp# chmod o+rx my-blog_linux_arm64

And run the application.

$ root@ba300b47a479:/tmp# ./my-blog_linux_arm64

2019-09-03T17:09:08.193Z INFO [flogo.engine] - Starting app [ app-build ] with version [ 0.0.1 ]
2019-09-03T17:09:08.203Z INFO [flogo.engine] - Engine Starting...
2019-09-03T17:09:08.204Z INFO [flogo.engine] - Starting Services...
2019-09-03T17:09:08.211Z INFO [flogo] - ActionRunner Service: Started
2019-09-03T17:09:08.212Z INFO [flogo.engine] - Started Services
2019-09-03T17:09:08.212Z INFO [flogo.engine] - Starting Application...
2019-09-03T17:09:08.213Z INFO [flogo] - Starting Triggers...
2019-09-03T17:09:08.223Z INFO [flogo] - Trigger [ receive_http_message ]: Started
2019-09-03T17:09:08.224Z INFO [flogo] - Triggers Started
2019-09-03T17:09:08.225Z INFO [flogo.engine] - Application Started
2019-09-03T17:09:08.226Z INFO [flogo] - Listening on http://0.0.0.0:8081
2019-09-03T17:09:08.229Z INFO [flogo.engine] - Engine Started

Let's test the application

Add a new comment to the post with id 1 using our application:


$ curl -v --header "Content-Type: application/json" -d '{"body": "Great post.","author": "alnura"}' http://localhost:8081/posts/1/addComment

*   Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 8081 (#0)
> POST /posts/1/addComment HTTP/1.1
> Host: localhost:8081
> User-Agent: curl/7.54.0
> Accept: */*
> Content-Type: application/json
> Content-Length: 42
>
* upload completely sent off: 42 out of 42 bytes
< HTTP/1.1 200 OK
< Access-Control-Allow-Origin: *
< Date: Tue, 03 Sep 2019 17:15:53 GMT
< Content-Length: 0
<* Connection #0 to host localhost left intact

Check that the comment was added:

$curl http://localhost/comments?postId=1

[
  {
    "id": 1,
    "body": "some comment",
    "postId": 1
  },
  {
    "author": "alnura",
    "body": "Great post.",
    "postId": "1",
    "id": 2
  }
]