This system will read real-time data from various sources (for example, Pubtrans database regarding departures and arrivals) and convert those to GTFS real-time messages using a pipeline created with Apache Pulsar. The final step will publish the messages to different locations (such as MQTT brokers and blob storage).
General usage pattern is to build Docker images and then run them with docker-compose. Services are separated to different GitHub repositories, each containing the source code and the Dockerfile.
/bin-folder contains scripts to launch Docker images for Pulsar and Redis which are requirements for some of the services.
Overall system requirements for running the system are:
- Connection to a Pubtrans SQL Server database
- Connection to an MQTT broker
System Architecture & Components
- mqtt.hsl.fi vehicle positions in HFP format (all vehicles)
- hsl-mqtt-lab-a.cinfra.fi estimates for stop time (metros)
- Pubtrans ROI: estimates for stop time (bus and trams)
- Pubtrans DOI: static data (schedule, stops, routes)
- api.digitransit.fi/realtime/service-alerts/v1: not used
- OMM DB: service alerts (cancellations, disruptions)
- raildigitraffic2gtfsrt: train stop estimates (to be replaced by a service connected to ratadigitraffic)
- sm5.rt.hsl.fi: EKE message from SM5 trains
- MQTT Broker cmqttdv.cinfra.fi: vehicle position in GTFS-RT format (HSL displays at stops)
- Azure Blob storage: used for publishing vehicle position, trip updates and service alerts in GTFS-RT format (for Google Maps and 3rd-party applications) and for archiving messages (HFP and EKE) in CSV files
- MQTT Broker pred.rt.hsl.fi -> Reittiopas.fi: stop estimates in GTFS-RT format
- Note: this MQTT broker is intended to be used by HSL systems only. Its functionality can be changed without a notice and there is no guarantee that it will work for third-party applications.
- Graylog server: logs from all the microservices.
Components are stored in their own Github Repositories:
- transitdata-common contains generic components and shared constants.
- transitdata-cache-bootstrapper fills journey-metadata to Redis cache for the next step
- transitdata-pubtrans-source polls changes to Pubtrans database and publishes the events to Pulsar as "raw-data"
- transitdata-omm-cancellation-source reads OMM database and generates TripUpdate trip cancellations
- transitdata-omm-alert-source reads OMM database and generates internal service alert messages
- transitdata-stop-cancellation-source reads OMM database and generates internal service stop cancellation messages
- transitdata-rail-tripupdate-source reads GTFS-RT trip updates from Digitransit rail trip update API
- pulsar-mqtt-gateway subscribes to a MQTT topic and publishes raw MQTT messages to a Pulsar topic, can be used with any MQTT-based data source
- transitdata-hfp-deduplicator deduplicates messages. Despite the name, this application can be used for deduplicating other messages than just HFP messages
- transitdata-hfp-parser parses raw HFP messages received from MQTT broker
- transitdata-metro-ats-parser parses raw metro ATS messages received from MQTT broker
- transitdata-metro-ats-cancellation-source creates cancellation messages from metro ATS messages
- transitdata-stop-estimates creates higher-level data (StopEstimates) from the raw-data where the data source is abstracted (bus, metro, train)
- transitdata-tripupdate-processor reads the estimates and cancellations and generates GTFS-RT messages and publishes them to Pulsar
- transitdata-alert-processor reads internal service alert messages and generates GTFS-RT Service alerts
- transitdata-vehicleposition-processor generates GTFS-RT vehicle position messages from HFP messages
- transitdata-stop-cancellation-processor applies stop cancellations to GTFS-RT trip updates
- pulsar-mqtt-gateway routes Pulsar messages to MQTT broker
- transitdata-gtfsrt-full-publisher publishes GTFS-RT Full dataset
- transitdata-pulsar-monitoring creates information about the state of the current pipeline for monitoring purposes
- transitdata-hslalert-source reads trip cancellations from HSL public HTML API and generates TripUpdate cancellations. Not in use anymore.
Transitlog HFP components
- transitlog-alert-sink application for inserting service alerts to PostgreSQL
- transitlog-hfp-sink Insert HFP data from Pulsar to TimescaleDB
- transitdata-hfp-parser parses MQTT raw topic & payload into Protobuf with HFP schema
- transitdata-hfp-deduplicator deduplicate data read from Pulsar topic(s)
- mqtt-pulsar-gateway application for reading data from MQTT topic and feeding it into Pulsar topic. This application doesn't care about the payload, it just transfers the bytes.
All the components in this project use semver, but the output conforms always to the GTFS Realtime standard. Some vendor-specific extensions might be added, which require incrementing the major version. Otherwise, new features should only increment the minor version, but some exceptions might arise. TripUpdate and ServiceAlert APIs are versioned independently.
Pulsar seems to cause approximately 5ms of latency for each message, which is consistent with their promise. The latency is not a problem in itself, and is well within acceptable bounds. However, the latency means that a single-threaded consumer-producer loop can only process 200 messages per second.