A framework for pluggable business logic components.
The package can be installed by adding opus
to your list of dependencies in mix.exs
:
def deps do
[{:opus, "~> 0.8"}]
end
- Each Opus pipeline module has a single entry point and returns tagged tuples
{:ok, value} | {:error, error}
- A pipeline is a composition of stateless stages
- A stage returning
{:error, _}
halts the pipeline - A stage may be skipped based on a condition function (
:if
and:unless
options) - Exceptions are converted to
{:error, error}
tuples by default - An exception may be left to raise using the
:raise
option - Each stage of the pipeline is instrumented. Metrics are captured automatically (but can be disabled).
- Errors are meaningful and predictable
defmodule ArithmeticPipeline do
use Opus.Pipeline
step :add_one, with: &(&1 + 1)
check :even?, with: &(rem(&1, 2) == 0), error_message: :expected_an_even
tee :publish_number, if: &Publisher.publishable?/1, raise: [ExternalError]
step :double, if: :lucky_number?
step :divide, unless: :lucky_number?
step :randomize, with: &(&1 * :rand.uniform)
link JSONPipeline
def double(n), do: n * 2
def divide(n), do: n / 2
def lucky_number?(n) when n in 42..1337, do: true
def lucky_number?(_), do: false
end
ArithmeticPipeline.call(41)
# {:ok, 84.13436750126804}
Read this blogpost to get started.
The core aspect of this library is defining pipeline modules. As in the
example above you need to add use Opus.Pipeline
to turn a module into
a pipeline. A pipeline module is a composition of stages executed in
sequence.
There are a few different types of stages for different use-cases.
All stage functions, expect a single argument which is provided either
from initial call/1
of the pipeline module or the return value of the
previous stage.
An error value is either :error
or {:error, any}
and anything else
is considered a success value.
This stage processes the input value and with a success value the next
stage is called with that value. With an error value the pipeline is
halted and an {:error, any}
is returned.
This stage is intended for validations.
This stage calls the stage function and unless it returns true
it
halts the pipeline.
Example:
defmodule CreateUserPipeline do
use Opus.Pipeline
check :valid_params?, with: &match?(%{email: email} when is_bitstring(email), &1)
# other stages to actually create the user
end
This stage is intended for side effects, such as a notification or a call to an external system where the return value is not meaningful. It never halts the pipeline.
This stage is to link with another Opus.Pipeline module. It calls
call/1
for the provided module. If the module is not an
Opus.Pipeline
it is ignored.
The skip
macro can be used for linked pipelines.
A linked pipeline may act as a true bypass, based on a condition,
expressed as either :if
or :unless
. When skipped, none of the stages
are executed and it returns the input, to be used by any next stages of
the caller pipeline. A very common use-case is illustrated in the following example:
defmodule RetrieveCustomerInformation do
use Opus.Pipeline
check :valid_query?
link FetchFromCache, if: :cacheable?
link FetchFromDatabase, if: :db_backed?
step :serialize
end
With skip
it can be written as:
defmodule RetrieveCustomerInformation do
use Opus.Pipeline
check :valid_query?
link FetchFromCache
link FetchFromDatabase
step :serialize
end
A linked pipeline becomes:
defmodule FetchFromCache do
use Opus.Pipeline
skip :assert_suitable, if: :cacheable?
step :retrieve_from_cache
end
The behaviour of each stage can be configured with any of the available options:
:with
: The function to call to fulfill this stage. It can be an Atom referring to a public function of the module, an anonymous function or a function reference.:if
: Makes a stage conditional, it can be either an Atom referring to a public function of the module, an anonymous function or a function reference. For the stage to be executed, the condition must returntrue
. When the stage is skipped, the input is forwarded to the next step if there's one.:unless
: The opposite of the:if
option, executes the step only when the callback function returnsfalse
.:raise
: A list of exceptions to not rescue. Defaults tofalse
which converts all exceptions to{:error, %Opus.PipelineError{}}
values halting the pipeline.:error_message
: An error message to replace the original error when a stage fails. It can be a String or Atom, which will be used directly in place of the original message, or an anonymous function, which receives the input of the failed stage and must return the error message to be used.:retry_times
: How many times to retry a failing stage, before halting the pipeline.:retry_backoff
: A backoff function to provide delay values for retries. It can be an Atom referring to a public function in the module, an anonymous function or a function reference. It must return anEnumerable.t
yielding at least as many numbers as theretry_times
.:instrument?
: A boolean which defaults totrue
. Set tofalse
to skip instrumentation for a stage.
defmodule ExternalApiPipeline do
use Opus.Pipeline
step :http_request, retry_times: 8, retry_backoff: fn -> linear_backoff(10, 30) |> cap(100) end
def http_request(_input) do
# code for the actual request
end
end
The above module, will retry be retried up to 8 times, each time applying a delay from the next value of the retry_backoff function, which returns a Stream.
All the functions from the :retry package will be available to be used in retry_backoff
.
You can select the stages of a pipeline to run using call/2
with the :except
and :only
options.
Example:
# Runs only the stage with the :validate_params name
CreateUserPipeline.call(params, only: [:validate_params]
# Runs all the stages except the selected ones
CreateUserPipeline.call(params, except: :send_notification)
Instrumentation hooks which can be defined:
:pipeline_started
: Called before a pipeline module is called:before_stage
: Called before each stage:stage_skipped
: Called when a conditional stage was skipped:stage_completed
: Called after each stage:pipeline_completed
: Called after pipeline module has returned
You can disable all instrumentation callbacks for a stage using instrument?: false
.
defmodule ArithmeticPipeline do
use Opus.Pipeline
step :double, instrument?: false
end
You can define module specific instrumentation callbacks using:
defmodule ArithmeticPipeline do
use Opus.Pipeline
step :double, with: &(&1 * 2)
step :triple, with: &(&1 * 3)
instrument :before_stage, fn %{input: input} ->
IO.inspect input
end
# Will be called only for the matching stage
instrument :stage_completed, %{stage: %{name: :triple}}, fn %{time: time} ->
# send to the monitoring tool of your choice
end
end
You can define a default instrumentation module for all your pipelines
by adding in your config/*.exs
:
config :opus, :instrumentation, YourModule
# but you may choose to provide a list of modules
config :opus, :instrumentation, [YourModuleA, YourModuleB]
An instrumentation module has to export instrument/3
functions like:
defmodule CustomInstrumentation do
def instrument(:pipeline_started, %{pipeline: ArithmeticPipeline}, %{input: input}) do
# publish the metrics to specific backend
end
def instrument(:before_stage, %{stage: %{pipeline: pipeline}}, %{input: input}) do
# publish the metrics to specific backend
end
def instrument(:stage_completed, %{stage: %{pipeline: ArithmeticPipeline}}, %{time: time}) do
# publish the metrics to specific backend
end
def instrument(:pipeline_completed, %{pipeline: ArithmeticPipeline}, %{result: result, time: total_time}) do
# publish the metrics to specific backend
end
def instrument(_, _, _), do: nil
end
Opus includes an instrumentation module which emits events using the :telemetry
library.
To enable it, change your config/config.exs
with:
config :opus, :instrumentation, [Opus.Telemetry]
Browse the available events here.
For instructions to integrate Opus Telemetry metrics in your Phoenix application, read this post.
You may choose to provide some common options to all the stages of a pipeline.
:raise
: A list of exceptions to not rescue. When set totrue
, Opus does not handle any exceptions. Defaults tofalse
which converts all exceptions to{:error, %Opus.PipelineError{}}
values halting the pipeline.:instrument?
: A boolean which defaults totrue
. Set tofalse
to skip instrumentation for a module.
defmodule ArithmeticPipeline do
use Opus.Pipeline, instrument?: false, raise: true
# The pipeline opts will disable instrumentation for this module
# and will not rescue exceptions from any of the stages
step :double, with: &(&1 * 2)
step :triple, with: &(&1 * 3)
end
You may visualise your pipelines using Opus.Graph
:
Opus.Graph.generate(:your_app)
# => {:ok, "Graph file has been written to your_app_opus_graph.png"}
โ This feature requires the opus_graph
package to be installed, add it in your
mix.exs.
defp deps do
{:opus_graph, "~> 0.1", only: [:dev]}
end
First make sure to add graphvix
to your dependencies:
# in mix.exs
defp deps do
[
{:opus, "~> 0.5"},
{:graphvix, "~> 0.5", only: [:dev]}
]
end
This feature uses graphviz, so make sure to have it installed. To install it:
# MacOS
brew install graphviz
# Debian / Ubuntu
apt-get install graphviz
Opus.Graph
is in fact a pipeline and its visualisation is:
You can customise the visualisation:
Opus.Graph.generate(:your_app, %{filetype: :svg})
# => {:ok, "Graph file has been written to your_app_opus_graph.svg"}
Read the available visualisation options here.
- Quiqup Engineering - How to Create Beautify Pipelines with Opus
- Pagerduty - How I Centralized our Scattered Business Logic Into One Clear Pipeline for our Elixir Webhook Service
- A Slack bookmarking application in Elixir with Opus
- Opus Telemetry
Using Opus in your company / project?
Let us know by submitting an issue describing how you use it.
Copyright (c) 2018 Dimitris Zorbas, MIT License. See LICENSE.txt for further details.