yggdrasil v2.0.0 Yggdrasil
Yggdrasil is an immense mythical tree that connects the nine worlds in Norse cosmology.
Yggdrasil
manages subscriptions to channels/queues in several brokers with
the possibility to add more. Simple Redis, RabbitMQ and Postgres adapters
are implemented. Message passing is done through
YProcess
. YProcess
allows to use
Phoenix.PubPub
as a pub/sub to distribute messages between processes.
Example using Redis
iex(1)> channel = %Yggdrasil.Channel{channel: "redis_channel",
...(1)> decoder: Yggdrasil.Decoder.Default.Redis}
iex(2)> Yggdrasil.subscribe(channel)
Then in redis:
127.0.0.1:6379> PUBLISH "redis_channel" "hello"
(integer) (1)
And finally if you flush in your iex
you’ll see the message received
by the Elixir shell:
iex(3> flush()
{:Y_CAST_EVENT, "redis_channel", "hello"}
:ok
Things to note:
- Every message coming from a broker (Redis, RabbitMQ, Postgres) will be like:
{:Y_CAST_EVENT, channel, message}
- The process calling
Yggdrasil.subscribe/1
will be the one that subscribes to the channel
Example using <code class="inline">GenServer</code>
The previous example can be wrapped inside a GenServer
defmodule Subscriber do
use GenServer
###################
# Client functions.
def start_link(channel, opts \ []) do
GenServer.start_link(__MODULE__, channel, opts)
end
def stop(subscriber, reason \ :normal) do
GenServer.stop(subscriber, reason)
end
######################
# GenServer callbacks.
def init(channel) do
Yggdrasil.subscribe(channel)
{:ok, channel}
end
def handle_info({:Y_CAST_EVENT, channel, message}, state) do
IO.inspect %{channel: channel, message: message}
{:noreply, state}
end
def terminate(_reason, channel) do
Yggdrasil.unsubscribe(channel)
:ok
end
end
````
So in `iex`:
iex(1)> channel = %Yggdrasil.Channel{channel: “redis_channel”, …(1)> decoder: Yggdrasil.Decoder.Default.Redis} iex(2)> {:ok, subscriber} = Subscriber.start_link(channel) iex(3)>
Again in Redis:
127.0.0.1:6379> PUBLISH “redis_channel” “hello” (integer) (1)
And finally you'll see in your `iex` the following:
%{channel: “redis_channel”, message: “hello”} iex(3)>
## Example using `YProcess`
`YProcess` is a `GenServer` wrapper with pubsub capabilities and it has
great sinergy with [`Yggdrasil`](Yggdrasil.html#content). The previous example implemented with
`YProcess` would be:
defmodule YSubscriber do use YProcess, backend: Yggdrasil.Backend
################### # Client functions.
def start_link(channel, opts \ []) do
YProcess.start_link(__MODULE__, channel, opts)
end
def stop(subscriber, reason \ :normal) do
YProcess.stop(subscriber, reason)
end
##################### # YProcess callbacks.
def init(channel) do
{:join, [channel], channel}
end
def handle_event(channel, message, state) do
IO.inspect %{channel: channel, message: message}
{:noreply, state}
end end
So in `iex`:
iex(1)> channel = %Yggdrasil.Channel{channel: “redis_channel”, …(1)> decoder: Yggdrasil.Decoder.Default.Redis} iex(2)> {:ok, y_subscriber} = YSubscriber.start_link(channel) iex(3)>
Again in Redis:
127.0.0.1:6379> PUBLISH “redis_channel” “hello” (integer) (1)
And finally you'll see in your `iex` the following:
%{channel: “redis_channel”, message: “hello”} iex(3)>
## Yggdrasil Channels
[`Yggdrasil`](Yggdrasil.html#content) channels have the name of the channel in the broker and the
name of the module of the message decoder. A decoder module also defines
which adapter should be used to connect to the channel.
%Yggdrasil.Channel{channel: “channel”, decoder: Yggdrasil.Decoder.Default.Redis}
The previous example will tell Yggdrasil to subscribe to the channel `"channel"`.
The decoder module [`Yggdrasil.Decoder.Default.Redis`](Yggdrasil.Decoder.Default.Redis.html) defined Redis as the broker
and does not change the message coming from Redis before sending it to the
subscribers.
### Decoders
The current [`Yggdrasil`](Yggdrasil.html#content) version has the following decoder modules:
* [`Yggdrasil.Decoder.Default`](Yggdrasil.Decoder.Default.html): Does nothing to the message and uses the
[`Yggdrasil.Adapter.Elixir`](Yggdrasil.Adapter.Elixir.html).
* [`Yggdrasil.Decoder.Default.Redis`](Yggdrasil.Decoder.Default.Redis.html): Does nothing to the message and uses the
[`Yggdrasil.Adapter.Redis`](Yggdrasil.Adapter.Redis.html).
* `Yggdrasil.Decoder.Default.RebbitMQ`: Does nothing to the message and uses the
[`Yggdrasil.Adapter.RabbitMQ`](Yggdrasil.Adapter.RabbitMQ.html).
* [`Yggdrasil.Decoder.Default.Postgres`](Yggdrasil.Decoder.Default.Postgres.html): Does nothing to the message and uses the
[`Yggdrasil.Adapter.Postgres`](Yggdrasil.Adapter.Postgres.html).
> For more information about adapters, see the Adapters section.
To implement a decoder is necessary to implement the `decode/2` callback for
[`Yggdrasil.Decoder`](Yggdrasil.Decoder.html) behaviour, i.e. subscribe to a Redis channel `"test"` that
publishes JSON. The subscribers must receive a map instead of a string with the
JSON.
defmodule CustomDecoder do use Yggdrasil.Decoder, adapter: Yggdrasil.Adapter.Redis
def decode(_channel, message) do
Poison.decode!(message)
end end
To subscribe to this channel, clients must use the following [`Yggdrasil`](Yggdrasil.html#content) channel:
%Yggdrasil.Channel{channel: “test”, decoder: CustomDecoder}
### Adapters
The current [`Yggdrasil`](Yggdrasil.html#content) version has the following adapters:
* [`Yggdrasil.Adapter.Elixir`](Yggdrasil.Adapter.Elixir.html): Message distribution using Elixir messages.
* [`Yggdrasil.Adapter.Redis`](Yggdrasil.Adapter.Redis.html): Messages come from a Redis channel.
* [`Yggdrasil.Adapter.RabbitMQ`](Yggdrasil.Adapter.RabbitMQ.html): Messages come from a RabbitMQ queue. A
`channel` is a tuple that contains the exchange and the routing key:
`{exchange, routing_key}`.
* [`Yggdrasil.Adapter.Postgres`](Yggdrasil.Adapter.Postgres.html): Messages come from the notifies of a
PostgreSQL database.
Also the function [`Yggdrasil.publish/2`](Yggdrasil.html#publish/2) is used to simulate published messages
by any of the brokers.
To implement a new adapter is necessary to use a `GenServer` or any wrapper over
`GenServer`. For more information, see the source code of any of the implemented
adapters.
## Installation
[`Yggdrasil`](Yggdrasil.html#content) is available as a Hex package. To install, add it to your
dependencies in your `mix.exs` file:
def deps do [{:yggdrasil, "~> 2.0.0"}] end
and ensure [`Yggdrasil`](Yggdrasil.html#content) is started before your application:
def application do [applications: [:yggdrasil]] end
## Configuration
[`Yggdrasil`](Yggdrasil.html#content) uses `YProcess` as a means to distribute the messages. So it is
necessary to provide a configuration for `YProcess` if you want to use, for
example, `Phoenix.PubSub` as your pubsub, i.e:
use Mix.Config
config :y_process, backend: YProcess.Backend.PhoenixPubSub, name: Yggdrasil.PubSub, adapter: Phoenix.PubSub.PG2, options: [pool_size: 10]
by default, `YProcess` will use `YProcess.Backend.PG2` as default backend.
For [`Yggdrasil`](Yggdrasil.html#content), there's only one general configuration parameter which is
the process name registry. By default, it uses `ExReg`, which is a simple but
rich process name registry. It is possible to use another one like `:gproc`.
use Mix.Config
config :yggdrasil, registry: :gproc
Specific configuration parameters are as follows:
* To configure [`Yggdrasil`](Yggdrasil.html#content) with the provided Redis adapter
([`Yggdrasil.Adapter.Redis`](Yggdrasil.Adapter.Redis.html)):
use Mix.Config
config :yggdrasil,
redis: [host: "localhost",
port: 6379,
password: "my password"]
The default Redis adapter uses `Redix`, so the configuration parameters have
the same name as the ones in `Redix`. By default connects to `redis://localhost`.
* To configure [`Yggdrasil`](Yggdrasil.html#content) with the provided RabbitMQ adapter
([`Yggdrasil.Adapter.RabbitMQ`](Yggdrasil.Adapter.RabbitMQ.html)):
use Mix.Config
config :yggdrasil,
rabbitmq: [host: "localhost",
port: 5672,
username: "guest",
password: "guest",
virtual_host: "/"]
The default RabbitMQ adapter uses `AMQP`, so the configuration parameters have
the same name as the ones in `AMQP`. By default connects to
`amqp://guest:guest@localhost/`
* To configure [`Yggdrasil`](Yggdrasil.html#content) with the provided PostgreSQL adapter
([`Yggdrasil.Adapter.Postgres`](Yggdrasil.Adapter.Postgres.html)):
use Mix.Config
postgres: [hostname: "localhost",
port: 5432,
username: "postgres",
password: "postgres",
database: "yggdrasil"]
The default PostgreSQL adapter uses `Postgrex`, so the configuration parameters
have the same name as the ones in `Postgrex`.
Summary
Functions
Emits a message
in a channel
. Bypasses the adapter
Subscribes to a channel
Unsubscribe from a channel