View Source Offbroadway EventRelay Producer
This producer allows you to stream events from EventRelay and process them using Broadway.
A lot of inspiration, code, and documentation been borrowed from the Google Cloud Pub/Sub Producer
Installation
If available in Hex, the package can be installed
by adding ` to your list of dependencies in
mix.exs: ```elixir def deps do [ {:offbroadway_eventrelay, "~> 0.1.0"} ] end ``` ## Guide EventRelay is a self-hosted real-time event streaming service. This guide assumes that you have EventRelay installed locally and that it can be accessed on localhost. ## Getting Started In order to use Broadway with EventRelay you need to: 1. [Install](https://github.com/eventrelay/eventrelay/wiki/Getting-Started) EventRelay 1. Configure your Elixir project to use Broadway 1. Define your pipeline configuration 1. Implement Broadway callbacks 1. Run the Broadway pipeline 1. Tune the configuration (Optional) If you are just getting familiar with EventRelay, refer to [the wiki](https://github.com/eventrelay/eventrelay/wiki) to get started. If you have an existing EventRelay instance, topic, subscription, and API Key, you can skip [step 1](#configure-eventrelay) and jump to [Start a new project](#starting-a-new-project) section. ## Configure EventRelay You will first need a running instance of EventRelay. If you don't have one see the [Getting Started](https://github.com/eventrelay/eventrelay/wiki/Getting-Started) guide. Login to EventRelay's web [UI](http://localhost:9000/users/log_in) The login credentials can be found in the [seeds file](https://github.com/eventrelay/eventrelay/blob/main/priv/repo/seeds.exs#L24). email: "user@example.com" password: "password123!@" Create a new topic: Name: users Create a new subscription: Name: Users Stream Type: api Topic: users You will need the subscription ID later to configure the Broadway Producer. Create an API Key: Name: Broadway Producer Status: active Type: consumer TLS Hostname: localhost You will need to the token, TLS certificate and key files that are generated for the API Key later to configure the Broadway Producer. ### Starting a new project If you plan to start a new project, just run: $ mix new my_app --sup The
--supflag instructs Elixir to generate an application with a supervision tree. ### Setting up dependencies Add
:offbroadwayeventrelayto the list of dependencies in
mix.exsdefp deps() do [ ... {:offbroadway_eventrelay, "~> 0.1"}, ] end Don't forget to check for the latest version of dependencies. ## Define the pipeline configuration Broadway is a process-based behaviour and to define a Broadway pipeline, we need to define three functions:
start_link/1,
handle_message/3and
handle_batch/4. We will cover
start_link/1in this section and the
handlecallbacks in the next one. Similar to other process-based behaviour,
startlink/1simply delegates to
Broadway.startlink/2`, which should define the producers, processors, and batchers in the
Broadway pipeline.
defmodule MyBroadway do
use Broadway
alias Broadway.Message
def startlink(opts) do
Broadway.startlink(__MODULE,
name: __MODULE,
producer: [
module:
{Offbroadway.EventRelay.Producer,
subscription_id: "{subscription_id}",
host: "localhost",
port: "50051",
token: "{token}", # Part of API Key
certfile: "/path/to/api_key_certfile.pem", # Part of API Key
keyfile: "/path/to/api_key_keyfile.pem", # Part of API Key
cacertfile: "/path/to/cacertfile.pem"} # From initial EventRelay installation
],
processors: [
default: []
],
batchers: [
default: [
batch_size: 10,
batch_timeout: 2_000
]
]
)
end
...callbacks...
end
For a full list of options for Offbroadway.EventRelay.Producer
, please see the
documentation.
For general information about setting up Broadway, see Broadway
module docs as well as
Broadway.start_link/2
.
## Implement Broadway callbacks
In order to process incoming messages, we need to implement the required callbacks. For the sake
of simplicity, we're considering that all messages received from the queue are strings and our
processor calls String.upcase/1
on them:
defmodule MyBroadway do
use Broadway
alias Broadway.Message
...start_link...
def handle_message(, %Message{data: data} = message, ) do
message
|> Message.update_data(fn data ->
first_name = get_in(data, ["person", "first_name"])
String.upcase(to_string(first_name))
end)
end
def handle_batch(, messages, , ) do
list = messages |> Enum.map(fn e -> e.data end)
IO.inspect(list, label: "Got batch of finished jobs from processors.")
messages
end
end
We are not doing anything fancy here, but it should be enough for our purpose. First we update the
message's data individually inside handle_message/3
and then we print each batch inside
handle_batch/4
.
For more information, see Broadway.handle_message/3
and Broadway.handle_batch/4
.
## Run the Broadway pipeline
To run your Broadway
pipeline, you need to add it as a child in a supervision tree. Most
applications have a supervision tree defined at lib/my_app/application.ex
. You can add Broadway
as a child to a supervisor as follows:
children = [
{MyBroadway, []}
]
Supervisor.startlink(children, strategy: :oneforone)
Now the Broadway pipeline should be started when your application starts. Also, if your Broadway
pipeline has any dependency (for example, it needs to talk to the database), make sure that
it is listed after its dependencies in the supervision tree.
If you followed the previous section about setting the project with gcloud
, you can now test the
the pipeline. In one terminal tab start the application:
$ iex -S mix
And in another tab, send a couple of test messages to EventRelay:
$ grpcurl -H "Authorization: Bearer {token}" -key /path/to/apikey_keyfile.pem -cert /path/to/api_key_certfile.pem -cacert /path/to/cacertfile.pem -proto event_relay.proto -d '{"topic": "users", "durable": true, "events": [{"name": "user.created", "data": "{\"person\": {\"first_name\": \"Bill\", \"last_name\": \"Roberts\", \"twitter_url\": \"https://twitter.com/billroberts\", \"uuid\": \"6131e043-52eb-4112-82f0-2817149b0e22\"}}", "source": "MyApp", "context": {"ip_address": "127.0.0.1"}}]}' localhost:50051 eventrelay.Events.PublishEvents
$ grpcurl -H "Authorization: Bearer {token}" -key /path/to/api_key_keyfile.pem -cert /path/to/api_key_certfile.pem -cacert /path/to/cacertfile.pem -proto event_relay.proto -d '{"topic": "users", "durable": true, "events": [{"name": "user.created", "data": "{\"person\": {\"first_name\": \"Betty\", \"last_name\": \"Roberts\", \"twitter_url\": \"https://twitter.com/bettyroberts\", \"uuid\": \"6131e043-52eb-4112-82f0-2817149b0e22\"}}", "source": "MyApp", "context": {"ip_address": "127.0.0.1"}}]}' localhost:50051 eventrelay.Events.PublishEvents
Now, In the first tab, you should see output similar to:
Got batch of finished jobs from processors.: ["BILL", "BETTY"]
## Tuning the configuration
Some of the configuration options available for Broadway come already with a
"reasonable" default value. However those values might not suit your
requirements. Depending on the number of messages you get, how much processing
they need and how much IO work is going to take place, you might need completely
different values to optimize the flow of your pipeline. The concurrency
option
available for every set of producers, processors and batchers, among with
max_demand
, batch_size
, and batch_timeout
can give you a great deal
of flexibility.
The concurrency
option controls the concurrency level in each layer of
the pipeline.
See the notes on Producer concurrency
and Batcher concurrency
for details.
Here's an example on how you could tune them according to
your needs.
defmodule MyBroadway do
use Broadway
def start_link(_opts) do
Broadway.start_link(__MODULE,
name: __MODULE,
producer: [
...
concurrency: 10,
],
processors: [
default: [
concurrency: 100,
max_demand: 1,
]
],
batchers: [
default: [
batch_size: 10,
concurrency: 10,
]
]
)
end
...callbacks...
end
In order to get a good set of configurations for your pipeline, it's
important to respect the limitations of the servers you're running,
as well as the limitations of the services you're providing/consuming
data to/from. Broadway comes with telemetry, so you can measure your
pipeline and help ensure your changes are effective.
Documentation can be generated with ExDoc
and published on HexDocs. Once published, the docs can
be found at https://hexdocs.pm/offbroadway_eventrelay.