judge-framework
Judge-Framework for decision making
The framework was shown first in code.talks commerce 2018 - Agile Transformation benötigt Einhörner
What is it?
You can share a link with your colleagues to get realtime evaluation of the voting.
How does it work?
We use MQTT protocol to build a pub/sub model. All messages are transfered through the public hivemq MQTT broker. We don't collect or send any sensitive data.
In detail:
Challenges:
- Share a unique link
- Distribute votings to all clients
- Sync new clients which joins later on
- Protect against double votes
- Protect against duplicate and out of order messages
Browser state
When a user shares a link we create a new unique subscription in form of judgeframework1.0/{group-id} and store the group id in the url.
Distribute votes
When a user visit the link and clicks on a voting card the decision is published to the subscription in (Step 1) and all participants will receive the event in order to be up-to-date.
Sync new and existing clients
In order to redeliver the latest state of the voting to clients which are out of sync we use the retain mechanism in the MQTT protocol. It allows to mark a published message as retain. A retain message is automatically published to all new and existing clients. The message contains the complete state of the latest voting. After each vote, the retain message gets overwritten and all following clients will receive the latest voting state.
Double votes
A user can't vote twice we persist the latest voted session in the local storage.
Message duplicates
Votes from clients can arrive more than once. We maintain a map of voted clients to protect against that.
Message order
Message order mustn't be guaranteed we are only interested in messages which increase the current state of a card 0-6.