Subscriptions Service Prototype

Overview

Supports subscription to public event topics (provided internally by either ActiveMQ or RabbitMQ) using STOMP over websockets (N.B. SockJS is not supported).

Clients can connect on port 9020 to the /subscriptions endpoint and subscribe to topic names of the form

public.somename
public.somename.someothername

etc. All topic names specified by clients must start with the prefix public. otherwise they will be rejected.

When subscribing to a topic, clients must supply a receipt header in the STOMP SUBSCRIBE frame in addition to the normal mandatory id header. The value of the receipt field can be any value, provided that it is unique for each new subscription. For this reason it is recommended to use a format of the form:

idOfClient-idWithinClient

This value will be returned by the Service in a RECEIPT frame to indicate successful creation of the subscxription and can thus be used to keep track of a client's active subscriptions. No receipt will be provided if the subscription attempt is unsuccessful, so clients should set a timeout after which, if no receipt is received, they will interpret the subscription attempt to have failed.

All common config for the application is stored in src/main/resources/application.yml and loaded via the BrokerConnection and WebSocket Records with broker specific setup in the appropriate adjacent subdirectory.

When deployed in Kubernetes, the settings under springConfig.config section of the Helm chart's values.yaml file are used to override those in the this file. To do this a further application.yaml file is written to the /opt/spring/config folder within the deployed container, which is referenced by the chart's ConfigMap.

Broker Initialisation

Either ActiveMQ or RabbitMQ can be run locally under podman using the Container files provided, which will establish a running instance of the selected broker with the standard setup expected by the subscription service.

To initialise your broker of choice run the container file from the appropriate subdirectory of resources. N.B you may need to chmod +x the file so that it is executable on your file system. So, for instance, to start ActiveMQ enter:

${YOUR_PROJECT_PATH}/src/main/resources/activemq/active

In either case, a broker image will be pulled from docker.io (assuming it is not already present in your image store) and run under podman with the appropriate settings. Once it has started succesfully, you can run the subscriptions service and it will connect on the standard STOMP port 61613 as the user subscription.

You cannot run both broker containers simultaneously as the ports will clash. If you want to switch to the other broker you will need to stop the service and then run podman stop <running container id>, before then executing the alternative container file. After this the subscriptions service can be restarted and will connect to the new broker.

For a Kubernetes the Helm chart expresses a dependency on the DAQ ActiveMQ Helm Chart caiusing it to be deployed to the active Namespace when the main application is. This has also been configured to setup the necessary users.