app.yaml

http_transport:
  transport_name: "httptransport"
  web_path: "/api/"
  web_port: 8889
  health_path: "/health-status/"
  reply_expected: True
  middleware:
    logging_mw: vumi.middleware.logging.LoggingMiddleware

rapidsms_relay_http:
  transport_name: 'httptransport'
  rapidsms_url: https://10.10.10.2/backend/vumi-http/
  web_path: /send/
  web_port: 9001
  send_to:
    default:
      transport_name: 'httptransport'
      from_addr: '1234' # not set automatically by SMSC
  middleware:
    logging_mw: vumi.middleware.logging.LoggingMiddleware

workers:
  smpp_transport: vumi.transports.smpp.SmppTransport
  http_transport: vumi.transports.api.api.HttpApiTransport
  rapidsms_relay_http: vumi.application.rapidsms_relay.RapidSMSRelay

rapidsms_settings.py

INSTALLED_BACKENDS = {
    #...
    "vumi-http": {
        "ENGINE":  "rapidsms.backends.vumi.VumiBackend",
        "sendsms_url": "http://10.10.10.4:9001/send/",
    },
}