TouK Hackathon – April 2021

The last time we wanted to organize a Hackathon our plans were thwarted by “you know what”. This state of affairs has lasted so long that we just couldn’t stand it anymore and launched the next edition of The Hackathon – remotely. This time we had to cope with new conditions – not all together in an open space, but everyone at home. We launched the communicator with a separate room per each project and went into action.
Here we present a brief summary from each team.

RCB Alert

tcb sms screenshot Every now and then we have a problem in our company – we need to inform everyone that the next day some loud redecorating is to take place or our air conditioning is to be cleaned – and we had better work remotely that day.
Unfortunately, sometimes our office managers gain this knowledge after our working hours, so there is no channel to notify everyone (hopefully – no one reads emails at home).

We found a solution to this problem during our last Hackathon.
We wrote a piece of software that orders an SMS to be sent to each person subscribed to TCB Alerts (it’s a pun on our government alerts – RCB).
This was the easy part – as we already had an SMS sending service.
However, we wanted this solution to be as easy as possible, so our office managers don’t have to open their laptops, connect to a VPN, search for special forms etc.
We decided to implement it as a hook to our communicator – RocketChat.
Now, when our office managers need to inform everyone in the evening, they need only to open the RocketChat app on their phone and type a message on a special channel – and that’s it!

We hope that this solution will help us to stay at home and work remotely during the days when it is inconvenient to work from the office.

TouK AboutMe

about me screenshot Currently at TouK we have several selfcare services providing information about TouKs (people working or cooperating with TouK).
The aim of our project was to join these services into one. Of course we know the rule that if you have three separate services then the worst approach is to add a new one. For this reason we enriched the most modern of them with new features such as TouK’s search, adding new information about people, teams information management and much more.
During the hackathon our team of four (+ the business owner) learnt a lot about frontend technologies such as CORS, MongoDB and LDAP.
We all hope that our work will prove to be useful for both current and future TouKs. Our team strove to provide a user experience so seamless that users would wonder at how easy selfcare management could be. We trust that with this hackathon we are a step closer to achieving that goal.

Business Config Manager

During our deployments of Nussknacker we often have the situation that the flow of development of scenarios was done by two teams. One of them is a team called “Configurators” – people who are close to business requirements but also with quite a high level of technical skills. Those people are responsible for the development of scenarios on the Nussknacker side. On the other hand, the second team is made up of Business members, those with lower technical skills but with a good knowledge of customer needs.
Configurators want to outsource some steps of development to business – so some changes can be made faster, without involving Configurators in the process. We found out that we should make a tool that can give Configurators the ability to create definitions of some configurations and after that, Business can fill in the values of those configurations. In the end, this configuration will be used in some steps of the scenario in Nussknacker.

After the deployment of the proof of concept, we realized that it is necessary to handle some important things:

  • Both definitions of configurations and values should be versioned and have some audit information, such as the author and time of the change.
  • Migrations of changes in definitions should be painless.
  • We should support many types of properties: from raw strings to some date time pickers and so on.
  • Configurations should have a lifecycle, so new ideas can be deployed on a lower environment and after some tests can be promoted to higher env.

After brainstorming before the Hackathon, we decided to use modern stack, but with some solid, battle-tested components:

We also designed the domain level of application.

On the first day of the Hackathon, we started with pair programming. We tried to go through all layers of the application to make sure that everyone in the team has a common vision of what the architecture will look like. After that we split the work into four separate parts:

  • Management of definitions
  • Management of values
  • Nussknacker integration with Business Config Service
  • Web application Finally, we integrated all the features together and completed the MVP step.

The project ended successfully. We proved that our design was correct, prepared a solid foundation for future development, and had a lot of fun designing the architecture and testing new tools.

Nussknacker Serverless

Most of you probably know Nussknacker – a powerful platform which allows non-technical users to author and deploy streaming scenarios on Apache Flink.
But Nussknacker Designer can also describe more business rules-oriented scenarios – used e.g. in recommendations or NBA domains. In this case, the scenario is deployed as a REST microservice. During the Hackathon we decided to make this setup more Kubernetes/Serverless-oriented. We decided that a Nussknacker scenario is a good candidate for K8 CRD and that KNative will provide us with a serverless deployment platform.
In two days we reached most of our goals:

  • Nussknacker creating scenario ConfigMap during deployment (in the future it will be CRD)
  • Custom Kubernetes operator/controller which transforms scenario ConfigMap into KNative service (scaling down to zero if needed :))
  • Simple REST microservice image, which serves the scenario
  • Everything deployed via Helm/GitlabCI to our DigitalOcean K8 cluster
    We are also pretty excited about the next steps – scenario observability (metrics, statuses), CRDs and making our serving image serverless ready – by using GraalVM native images.
    Hopefully, in the short to medium term, all of this will be accessible with our Nussknacker offering.


music box screenshot We have created a minimalistic web app for generating music in a loop based on text input.
The idea is to make writing music as easy as possible. E.g. |k h s h | is the most basic percussive beat, while |Am|C| gives a basic chord progression. Furthermore, there’s a collaborative mode (think jam sessions ;).




In our opinion, The Hackathon was successful and fulfilled its task – that is, it allowed us to take a short break from our more important work and experiment with various fun technologies in good company. The fact that during the Hackathon team members were in a voice chat with each other certainly played a big role, which to some extent allowed us to build an atmosphere of cooperation in the fight against challenges.
We are already looking forward to the next hackathon – hopefully, this time on site.

If you want, here you can see what we did during the previous edition.

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Grails session timeout without XML

This article shows clean, non hacky way of configuring featureful event listeners for Grails application servlet context. Feat. HttpSessionListener as a Spring bean example with session timeout depending on whether user account is premium or not.

Common approaches

Speaking of session timeout config in Grails, a default approach is to install templates with a command. This way we got direct access to web.xml file. Also more unnecessary files are created. Despite that unnecessary files are unnecessary, we should also remember some other common knowledge: XML is not for humans.

Another, a bit more hacky, way is to create mysterious scripts/_Events.groovy file. Inside of which, by using not less enigmatic closure: eventWebXmlEnd = { filename -> ... }we can parse and hack into web.xml with a help of XmlSlurper.
Even though lot of Grails plugins do it similar way, still it’s not really straightforward, is it? Besides, where’s the IDE support? Hello!?

Examples of both above ways can be seen on StackOverflow.

Simpler and cleaner way

By adding just a single line to the already generated init closure we have it done:
class BootStrap {

def init = { servletContext ->

Allrighty, this is enough to avoid XML. Sweets are served after the main course though :)

Listener as a Spring bean

Let us assume we have a requirement. Set a longer session timeout for premium user account.
Users are authenticated upon session creation through SSO.

To easy meet the requirements just instantiate the CustomTimeoutSessionListener as Spring bean at resources.groovy. We also going to need some source of the user custom session timeout. Let say a ConfigService.
beans = {    
customTimeoutSessionListener(CustomTimeoutSessionListener) {
configService = ref('configService')

With such approach BootStrap.groovy has to by slightly modified. To keep control on listener instantation, instead of passing listener class type, Spring bean is injected by Grails and the instance passed:
class BootStrap {

def customTimeoutSessionListener

def init = { servletContext ->

An example CustomTimeoutSessionListener implementation can look like:
import javax.servlet.http.HttpSessionEvent    
import javax.servlet.http.HttpSessionListener

class CustomTimeoutSessionListener implements HttpSessionListener {

ConfigService configService

void sessionCreated(HttpSessionEvent httpSessionEvent) {
httpSessionEvent.session.maxInactiveInterval = configService.sessionTimeoutSeconds

void sessionDestroyed(HttpSessionEvent httpSessionEvent) { /* nothing to implement */ }
Having at hand all power of the Spring IoC this is surely a good place to load some persisted user’s account stuff into the session or to notify any other adequate bean about user presence.

Wait, what about the user context?

Honest answer is: that depends on your case. Yet here’s an example of getSessionTimeoutMinutes() implementation using Spring Security:

class ConfigService {

static final int 3H = 3 * 60 * 60
static final int QUARTER = 15 * 60

int getSessionTimeoutSeconds() {

String username = SecurityContextHolder.context?.authentication?.principal
def account = Account.findByUsername(username)

return account?.premium ? 3H : QUARTER
This example is simplified. Does not contain much of defensive programming. Just an assumption that principal is already set and is a String - unique username. Thanks to Grails convention our ConfigService is transactional so the Account domain class can use GORM dynamic finder.
OK, config fetching implementation details are out of scope here anyway. You can get, load, fetch, obtain from wherever you like to. Domain persistence, principal object, role config, external file and so on...

Any gotchas?

There is one. When running grails test command, servletContext comes as some mocked class instance without addListener method. Thus we going to have a MissingMethodException when running tests :(

Solution is typical:
def init = { servletContext ->
if (Environment.current != Environment.TEST) {
An unnecessary obstacle if you ask me. Should I submit a Jira issue about that?


Just implement a HttpSessionListener. Create a Spring bean of the listener. Inject it into BootStrap.groovy and call servletContext.addListener(injectedListener).

Hibernate hbm2ddl won’t create schema before creating tables

Situation I have a local H2 in memory database for integration tests and an Oracle db for production. I do not control the Oracle DB model. The in memory H2 database is created automatically by adding <prop key="">update&l...Situation I have a local H2 in memory database for integration tests and an Oracle db for production. I do not control the Oracle DB model. The in memory H2 database is created automatically by adding <prop key="">update&l...