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Broadcast Interface

Step 2: Server config - broadcast interface​

1) Deploying the broadcast channel backbone service (optional)​

When scaling the OPAL Server to multiple workers and/or multiple containers, we use a broadcast channel to sync between all the instances of OPAL Server. In order words, communication on the broadcast channel is communication between OPAL servers, and is not related to the OPAL client.

Under the hood, our interface to the broadcast channel backbone service is implemented by encode/broadcaster.

At the moment, the supported broadcast channel backbones are:

  • Postgres LISTEN/NOTIFY
  • Redis
  • Kafka

Deploying the actual service used for broadcast (i.e: Redis) is outside the scope of this tutorial. The easiest way is to use a managed service (e.g: AWS RDS, AWS ElastiCache, etc), but you can also deploy your own dockers.

When running in production, you should run with multiple workers per server instance (i.e: container/node), if not multiple containers, and thus deploying the backbone service becomes mandatory for production environments.

2) Declaring the broadcast uri environment variable​

Declaring the broadcast uri is optional, depending on whether you deployed a broadcast backbone service and are also running with more than one OPAL server instance (multiple workers or multiple nodes). If you are running with multiple server instances (you should for production), declaring the broadcast uri is mandatory.

Env Var NameFunction
OPAL_BROADCAST_URI
  • Broadcast channel backend.

  • The format of the broadcaster URI string is specified

    here

    .

  • Note that password authentication is not supported in the broadcaster URI when using redis, see

    source

    .

  • Example value: OPAL_BROADCAST_URI=postgres://localhost/mydb

3) Declaring the number of uvicorn workers​

As we mentioned in the previous section, each container can run multiple workers, and if you use more than one, you need a broadcast channel.

This is how you define the number of workers (pay attention: this env var is not prefixed with OPAL_):

Env Var NameFunction
UVICORN_NUM_WORKERSthe number of workers in a single container (example value: 4)