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HASH Realtime

The realtime package connects to a Postgres instance and reads its change-stream by connecting to a logical replication slot created using the wal2json extension. Its purpose is to provide realtime updates on entities to a collection of subscribers, by pushing change messages onto pre-specified queues.

Configuration

The realtime service uses the following environment variables:

  • NODE_ENV: controls the logging level & formatting. Must be either "development" or "production".
  • HASH_PG_DATABASE: Postgres database name.
  • HASH_PG_PASSWORD: Postgres user password.
  • HASH_PG_USER: Postgres username.
  • HASH_PG_HOST: Postgres hostname.
  • HASH_PG_PORT: Postgres connection port.
  • HASH_REALTIME_PORT: (default: 3333) Service listening port.
  • HASH_SEARCH_QUEUE_NAME: The name of the queue to push changes for the search-loader service.
  • HASH_INTEGRATION_QUEUE_NAME: The name of the queue to push changes for collab in the api service. (default: integration)

Configuration for the tables to monitor and the queues to push messages to is defined in src/config.ts. The service will push all insert/update/delete changes from the tables specified in the MONITOR_TABLES array, to all queues specified in the QUEUES array.

Getting started

In dev mode, the service will automatically restart:

yarn dev

Production mode:

yarn start

For health checks, the service listens on port 3333 by default at the path /health-check. The port number may be overridden by setting HASH_REALTIME_PORT.

High Availability

To maintain message ordering, a single realtime instance retains exclusive read access to the logical replication slot. The service may operate in high-availibility mode where one or more instances wait in standby mode in while a single instance reads from the slot. In the event the owning instance crashes, a standby instance will automatically acquire ownership of the slot and begin reading.