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Application development

Generating service account tokens

If you'd like a third-party application to rely on the API of your application without authenticating using a user/password you can generate an access token with a fixed expiration date to be used as an API key.

Personal access token

If your API needs a user ID to work as expected first register a user as usual. Then, using your application secret and a JWT library, issue a JWT with a payload matching the configuration options of your application regarding audience (i.e. domain), issuer and the user ID in the sub claim if any, e.g.:

  "aud": "",
  "iss": "kalisio",
  "exp": 1552402010,
  "sub": "5bc5b166beb4648d3cd79327"


In local development environment aud=kalisio.

Impersonated access token

If you don't want to rely on an existing user with the appropriate permissions you can create a stateless token thant directly includes it, the payload of your token will be used as a virtual user object. For instance, if your app rely on a permissions field to compute user abilities you can provide a token like this:

  "aud": "",
  "iss": "kalisio",
  "exp": 1552402010,
  "sub": "myapp",
  "permissions": "superadmin"

In this case the sub claim is not used internally and can be used for instance to identify the owner of the token.


In local development environment aud=kalisio.

Linking errors

Due to the modular approach of the KDK we need to link the modules and the applications according to the dependency tree when developing.


Due to some changes in the way npm manages linked modules we prefer to use Yarn as a package manager.

It appeared that when performing a new install, adding a new dependency, or launching two installs concurrently, some of these links often break raising different errors:

  • TypeError: Cannot read property 'eventMappings' of undefined
  • TypeError: processNextTick is not a function
  • Error: Cannot find module 'safer-buffer'
  • An unexpected error occurred: "ENOENT: no such file or directory, scandir 'xxx'
  • ...

As a workaround you will either need to:

  • clear the yarn cache yarn cache clean (or yarn cache clean module to be more specific)
  • restore the broken links using commands like e.g. yarn link @kalisio/kdk in the broken applications
  • reinstall all dependencies using yarn install --check-files in broken modules/applications, and then restore the links as above


You might also clean all dependencies frist using rimraf node_modules


Errors are often visible when launching the app server but might come from an underlying module. For instance the TypeError: Cannot read property 'eventMappings' of undefined error often appears in modules, probably due to the fact incompatible versions of the same library (e.g. Feathers) are installed. So try first to reinstall and relink the modules before your app, and if you'd like to see if a module is fine running its tests is usually a good indicator: yarn mocha.

Profiling applications

In your local development environment you can usually use Chrome DevTools. However, it is trickier to perform profiling on remote production environments, here are the steps.

  1. Override the command used to launch your application to activate the Node.js V8 profiler:
node --prof app.js
  1. Once you have run your tests and recorded the profile, a file named like this isolate-pid-1-v8.log should appear in your working directory. Process it using the following commands to get either:
  • a "human-readable" file (txt)

    node --prof-process .\isolate-0x49489f0-1-v8.log > prof-processed.txt
  • a "machine-readable" file (json)

    node --prof-process --preprocess -j .\isolate-0x49489f0-1-v8.log > prof-processed.json
  1. In order to identify bottlenecks in your app you can either:
  • Analyze the human-readable file
  • Install flamebearer and generate the flame graph
npm install -g flamebearer
flamebearer prof-processed.json

Running multiple applications side-by-side

For instance, as Kano depends for some features on a running Weacast API you will need to run both on your local development environment. If your application also uses replication you will need to launch two instances in parallel. The problem is that by default all our apps uses the 8081 port for server and 8080 port for client in development mode, generating a port conflict. Similarly the Node.js debugger uses by default the 9229 port.

You should run the first server by defining eg. PORT=8082 (to avoid port conflict). If single-sign-on is expected to work, define also APP_SECRET=same value as in second application configuration as environment variables. Then execute the yarn dev:replica command (will setup the Node.js debugger to use the 9229 port to avoid port conflict). Last, you can launch the second server/client as usual.


You usually don't need the client application but only the API on the replica but if required you can launch another client similarly e.g. by setting CLIENT_PORT=8083.


If you need more than two side-by-side applications then use set NODE_OPTIONS environment variable before launching each one, e.g. NODE_OPTIONS='--inspect-port=9230'.

Application instances synchronization

If your application is not fully stateless or requires real-time events to be dispatched to clients you will also need to synchronize them using feathers-sync. We previously relied on the mubsub adapter because as we already use MongoDB it did not require any additional service to be deployed.

Unfortunately it has been deprecated. As a consequence we now rely on the Redis adapter. For development you can easily run a Redis server using Docker:

// Bind it to your prefered port
docker run -d --rm --name redis -p 6300:6379 redis:5

You will need to play with the different options presented above to avoid port conflicts and define as well how your app connects to the Redis instance using the REDIS_URL environment variable like redis:// You can see the subscriber apps and exchanged messages by connecting to the Redis container:

// Bind it to your prefered port
docker exec -it redis bash
> redis-cli
// Number of subscribers
> PUBSUB NUMSUB feathers-sync
1) "feathers-sync"
2) (integer) 2
// Monitor messages
> SUBSCRIBE feathers-sync
Reading messages...