This is customized to fit the needs of rentouch. Therefore it has hard-coded uri patterns inside.

WAMP does not support shared subscriptions. The issue is that when you want to share workload on multiple instances of backend-servers you are stuck to registrations. But you can not always use registrations. An example: Clients which publish their status-changes to all other peers. You may want to store the state of the client in the backend.

Having multiple backend-server instances also allow rolling upgrades without any downtime.

This server will check crossbar for registrations which have a defined pattern: com.x.y.SUB_z. The last part of the uri has to start with 'SUB_'.

After the event reaches the subToCall server we can decide if we want to transfer the data to the piplanning-server's via Redis or WAMP. WAMP is default, but you tell subToCall to use Redis by setting the env variable 'USE_REDIS_MQ' to 1.

• (-) As we try to use shared subscriptions to lower the load on our backend, we introduce a (new) bottle-neck with this 'forwarder' / server.
• (+) It uses the existing infrastructure.
• (+) We do not need to add a redis-puller on piplanning-server.

• (+) Does not introduce a new bottleneck as Redis can cache the events for a short period of time.
• (-) We do not know for sure if a event got handled by piplanning-server. The event could be lost.
• (-) The queue could get filled up heavily if all piplanning-server's crashed. This will result in a inconsistent state (single source of truth (piplanningserver) is not up to date)

Only works with Python3.x

• pip install -r requirements.txt

You can pass the following environment variables:

• WAMP_URL: url to crossbar (e.g. wss://demo.crossbar.com/ws/)
• CROSSBAR_REALM: crossbar-realm, default to 'realm1'
• BACKEND_USERNAME: username for WAMP-CRA authentication
• BACKEND_SECRET: secret for WAMP-CRA authentication

For more configuration checkout utils.py.