Broadway behaviour (Broadway v1.0.0) View Source
Broadway is a concurrent, multi-stage tool for building data ingestion and data processing pipelines.
It allows developers to consume data efficiently from different sources, such as Amazon SQS, Apache Kafka, Google Cloud PubSub, RabbitMQ and others.
Built-in features
Back-pressure - by relying on
GenStage
, we only get the amount of events necessary from upstream sources, never flooding the pipeline.Automatic acknowledgements - Broadway automatically acknowledges messages at the end of the pipeline or in case of errors.
Batching - Broadway provides built-in batching, allowing you to group messages either by size and/or by time. This is important in systems such as Amazon SQS, where batching is the most efficient way to consume messages, both in terms of time and cost.
Fault tolerance - Broadway pipelines are carefully designed to manage failures. Producers are isolated from the rest of the pipeline and automatically resubscribe to your data source in case of crashes. At the same time, all of your Broadway callbacks are stateless, which allows Broadway to handle any errors locally. This provides a stable foundation that play well with your producers, regardless if their delivery guarantees are at least once, at most once, or exactly once.
Graceful shutdown - Broadway integrates with the VM to provide graceful shutdown. By starting Broadway as part of your supervision tree, it will guarantee all events are flushed once the VM shuts down.
Built-in testing - Broadway ships with a built-in test API, making it easy to push test messages through the pipeline and making sure the event was properly processed.
Custom failure handling - Broadway provides a
handle_failed/2
callback where developers can outline custom code to handle errors. For example, if they want to move messages to another queue for further processing.Dynamic batching - Broadway allows developers to batch messages based on custom criteria. For example, if your pipeline needs to build batches based on the
user_id
, email address, etc, it can be done by callingBroadway.Message.put_batch_key/2
.Ordering and Partitioning - Broadway allows developers to partition messages across workers, guaranteeing messages within the same partition are processed in order. For example, if you want to guarantee all events tied to a given
user_id
are processed in order and not concurrently, you can set the:partition_by
option. See "Ordering and partitioning".Rate limiting: Broadway allows developers to rate limit all producers in a single node by a given number of messages in a time period, allowing developers to easily work sources or sinks that cannot cope with a high number of requests. See the ":rate_limiting" option for producers in
start_link/2
.Metrics - Broadway uses the
:telemetry
library for instrumentation, see "Telemetry" section below for more information.Back-off (TODO)
The Broadway Behaviour
In order to use Broadway, you need to:
- Define your pipeline configuration
- Define a module implementing the Broadway behaviour
Example
Broadway is a process-based behaviour, and you begin by
defining a module that invokes use Broadway
. Processes
defined by these modules will often be started by a
supervisor, and so a start_link/1
function is frequently
also defined but not strictly necessary.
defmodule MyBroadway do
use Broadway
def start_link(_opts) do
Broadway.start_link(MyBroadway,
name: MyBroadwayExample,
producer: [
module: {Counter, []},
concurrency: 1
],
processors: [
default: [concurrency: 2]
]
)
end
...callbacks...
end
Then add your Broadway pipeline to your supervision tree
(usually in lib/my_app/application.ex
):
children = [
{MyBroadway, []}
]
Supervisor.start_link(children, strategy: :one_for_one)
Adding your pipeline to your supervision tree in this way
calls the default child_spec/1
function that is generated
when use Broadway
is invoked. If you would like to customize
the child spec passed to the supervisor, you can override the
child_spec/1
function in your module or explicitly pass a
child spec to the supervisor when adding it to your supervision tree.
The configuration above defines a pipeline with:
- One producer
- Two processors
Here is how this pipeline would be represented:
[producer_1]
/ \
/ \
/ \
/ \
[processor_1] [processor_2] <- process each message
After the pipeline is defined, you need to implement the handle_message/3
callback which will be invoked by processors for each message.
handle_message/3
receives every message as a Broadway.Message
struct and it must return an updated message.
Batching
Depending on the scenario, you may want to group processed messages as batches before publishing your data. This is common and especially important when working with services like AWS S3 and SQS that provide a specific API for sending and retrieving batches. This can drastically increase throughput and consequently improve the overall performance of your pipeline.
To create batches, define the :batchers
configuration option:
defmodule MyBroadway do
use Broadway
def start_link(_opts) do
Broadway.start_link(MyBroadway,
name: MyBroadwayExample,
producer: [
module: {Counter, []},
concurrency: 1
],
processors: [
default: [concurrency: 2]
],
batchers: [
sqs: [concurrency: 2, batch_size: 10],
s3: [concurrency: 1, batch_size: 10]
]
)
end
# ...callbacks...
end
The configuration above defines a pipeline with:
- One producer
- Two processors
- One batcher named
:sqs
with two batch processors - One batcher named
:s3
with one batch processor
Here is how this pipeline would be represented:
[producer_1]
/ \
/ \
/ \
/ \
[processor_1] [processor_2] <- process each message
/\ /\
/ \ / \
/ \ / \
/ x \
/ / \ \
/ / \ \
/ / \ \
[batcher_sqs] [batcher_s3]
/\ \
/ \ \
/ \ \
/ \ \
[batch_sqs_1] [batch_sqs_2] [batch_s3_1] <- process each batch
Additionally, you have to define the handle_batch/4
callback,
which batch processors invoke for each batch. You can then
call Broadway.Message.put_batcher/2
inside handle_message/3
to
control which batcher the message should go to.
The batcher receives processed messages and creates batches
specified by the batch_size
and batch_timeout
configuration. The
goal is to create a batch with at most batch_size
entries within
batch_timeout
milliseconds. Each message goes into a particular batch,
controlled by calling Broadway.Message.put_batch_key/2
in
handle_message/3
. Once a batch is created in the batcher, it is sent
to a separate process (the batch processor) that will call handle_batch/4
,
passing the batcher, the batch itself (a list of messages), a Broadway.BatchInfo
struct, and the Broadway context.
For example, imagine your producer generates integers as data
.
You want to route the odd integers to SQS and the even ones to
S3. Your pipeline would look like this:
defmodule MyBroadway do
use Broadway
import Integer
alias Broadway.Message
# ...start_link...
@impl true
def handle_message(_, %Message{data: data} = message, _) when is_odd(data) do
message
|> Message.update_data(&process_data/1)
|> Message.put_batcher(:sqs)
end
def handle_message(_, %Message{data: data} = message, _) when is_even(data) do
message
|> Message.update_data(&process_data/1)
|> Message.put_batcher(:s3)
end
defp process_data(data) do
# Do some calculations, generate a JSON representation, etc.
end
@impl true
def handle_batch(:sqs, messages, _batch_info, _context) do
# Send batch of successful messages as ACKs to SQS
# This tells SQS that this list of messages were successfully processed
end
def handle_batch(:s3, messages, _batch_info, _context) do
# Send batch of messages to S3
end
end
See the callbacks documentation for more information on the arguments given to each callback and their expected return types.
The default batcher
Once you define the :batchers
configuration key for your Broadway pipeline,
then all messages get batched. By default, unless you call
Broadway.Message.put_batcher/2
, messages have their batcher set to the
:default
batcher. If you don't define configuration for it, Broadway is going
to raise an error.
For example, imagine you want to batch "special" messages and handle them differently then all other messages. You can configure your pipeline like this:
defmodule MyBroadway do
use Broadway
def start_link(_opts) do
Broadway.start_link(MyBroadway,
name: MyBroadwayExample,
producer: [
module: {Counter, []},
concurrency: 1
],
processors: [
default: [concurrency: 2]
],
batchers: [
special: [concurrency: 2, batch_size: 10],
default: [concurrency: 1, batch_size: 10]
]
)
end
def handle_message(_, message, _) do
if special?(message) do
Broadway.Message.put_batcher(:special)
else
message
end
end
def handle_batch(:special, messages, _batch_info, _context) do
# Handle special batch
end
def handle_batch(:default, messages, _batch_info, _context) do
# Handle all other messages in batches
end
Now you are ready to get started. See the start_link/2
function
for a complete reference on the arguments and options allowed.
Also makes sure to check out GUIDES in the documentation sidebar for more examples, how tos and more.
Acknowledgements and failures
At the end of the pipeline, messages are automatically acknowledged.
If there are no batchers, the acknowledgement will be done by processors.
The number of messages acknowledged, assuming the pipeline is running
at full scale, will be max_demand - min_demand
. Since the default values
are 10 and 5 respectively, we will be acknowledging in groups of 5.
If there are batchers, the acknowledgement is done by the batchers,
using the batch_size
.
In case of failures, Broadway does its best to keep the failures
contained and avoid losing messages. The failed message or batch is
acknowledged as failed immediately. For every failure, a log report
is also emitted. If your Broadway module also defines the
handle_failed/2
callback, that callback will be invoked with
all the failed messages before they get acknowledged.
Note however, that Broadway
does not provide any sort of retries
out of the box. This is left completely as a responsibility of the
producer. For instance, if you are using Amazon SQS, the default
behaviour is to retry unacknowledged messages after a user-defined
timeout. If you don't want unacknowledged messages to be retried,
is your responsibility to configure a dead-letter queue as target
for those messages.
Producer concurrency
Setting producer concurrency is a tradeoff between latency and internal queueing.
For efficiency, you should generally limit the amount of internal queueing. Whenever additional messages are sitting in a busy processor's mailbox, they can't be delivered to another processor which may be available or become available first.
One possible cause of internal queueing is multiple producers. This is because
each processor's demand will be sent to all producers. For example, if a
processor demands 2
messages and there are 2
producers, each producer
will try to produce 2
messages (for example, by pulling from a queue or
whatever the specific producer does) and give them to the processor. So the
processor may receive max_demand * <producer concurrency>
messages.
Setting producer concurrency: 1
will reduce internal queueing. This is
likely a good choice for producers which take minimal time to produce a
message, such as BroadwayRabbitMQ
, which receives messages as they are
pushed by RabbitMQ and can specify how many to prefetch.
On the other hand, when using a producer such as BroadwaySQS
which must
make a network round trip to fetch from an external source, it may be better
to use multiple producers and accept some internal queueing to avoid having
fetch messages whenever there is new demand.
Measure your system to decide which setting is most appropriate.
Adding another single-producer pipeline, or another node running the pipeline, are other ways you may consider to increase throughput.
Batcher concurrency
If a batcher's concurrency
is greater than 1
, Broadway will use as few of
the batcher processes as possible at any given moment, attempting to satisfy
the batch_size
of one batcher process within the batch_timeout
before
sending messages to another.
Testing
Many producers receive data from external systems and hitting the network is usually undesirable when running the tests.
For testing purposes, we recommend developers to use Broadway.DummyProducer
.
This producer does not produce any messages by itself and instead the
test_message/3
and test_batch/3
functions should be used to publish
messages.
With test_message/3
, you can push a message into the pipeline and receive
a process message when the pipeline acknowledges the data you have pushed
has been processed.
Let's see an example. Imagine the following Broadway
module:
defmodule MyBroadway do
use Broadway
def start_link() do
producer_module = Application.fetch_env!(:my_app, :producer_module)
Broadway.start_link(__MODULE__,
name: __MODULE__,
producer: [
module: producer_module
],
processors: [
default: []
],
batchers: [
default: [batch_size: 10]
]
)
end
@impl true
def handle_message(_processor, message, _context) do
message
end
@impl true
def handle_batch(_batcher, messages, _batch_info, _context) do
messages
end
end
Now in config/test.exs you could do:
config :my_app, :producer_module, {Broadway.DummyProducer, []}
And we can test it like this:
defmodule MyBroadwayTest do
use ExUnit.Case, async: true
test "test message" do
ref = Broadway.test_message(MyBroadway, 1)
assert_receive {:ack, ^ref, [%{data: 1}], []}
end
end
Note that at the end we received a message in the format of:
{:ack, ^ref, successful_messages, failure_messages}
You can use the acknowledgment to guarantee the message has been processed and therefore any side-effect from the pipeline should be visible.
When using test_message/3
, the message will be delivered as soon as
possible, without waiting for the pipeline batch_size
to be reached
or without waiting for batch_timeout
. This behaviour is useful to test
and verify single messages, without imposing high timeouts to our test
suites.
In case you want to test multiple messages, then you need to use
test_batch/3
. test_batch/3
will respect the batching configuration,
which most likely means you need to increase your test timeouts:
test "batch messages" do
{:ok, pid} = MyBroadway.start_link()
ref = Broadway.test_batch(pid, [1, 2, 3])
assert_receive {:ack, ^ref, [%{data: 1}, %{data: 2}, %{data: 3}], []}, 1000
end
However, keep in mind that, generally speaking, there is no guarantee the messages will arrive in the same order that you have sent them, especially for large batches, as Broadway will process large batches concurrently and order will be lost.
If you want to send more than one test message at once, then we recommend
setting the :batch_mode
to :bulk
, especially if you want to assert how
the code will behave with large batches. Otherwise the batcher will flush
messages as soon as possible and in small batches.
However, keep in mind that, regardless of the :batch_mode
you cannot
rely on ordering, as Broadway pipelines are inherently concurrent. For
example, if you send those messages:
test "multiple batch messages" do
{:ok, pid} = MyBroadway.start_link()
ref = Broadway.test_batch(pid, [1, 2, 3, 4, 5, 6, 7], batch_mode: :bulk)
assert_receive {:ack, ^ref, [%{data: 1}], []}, 1000
end
Ordering and partitioning
By default, Broadway processes all messages and batches concurrently,
which means ordering is not guaranteed. Some producers may impose some
ordering (for instance, Apache Kafka), but if the ordering comes from a
business requirement, you will have to impose the ordering yourself.
This can be done with the :partition_by
option, which enforces that
messages with a given property are always forwarded to the same stage.
In order to provide partitioning throughout the whole pipeline, just
set :partition_by
at the root of your configuration:
defmodule MyBroadway do
use Broadway
def start_link(_opts) do
Broadway.start_link(MyBroadway,
name: MyBroadwayExample,
producer: [
module: {Counter, []},
concurrency: 1
],
processors: [
default: [concurrency: 2]
],
batchers: [
sqs: [concurrency: 2, batch_size: 10],
s3: [concurrency: 1, batch_size: 10]
],
partition_by: &partition/1
)
end
defp partition(msg) do
msg.data.user_id
end
In the example above, we are partitioning the pipeline by user_id
.
This means any message with the same user_id
will be handled by
the same processor and batch processor.
The partition
function must return a non-negative integer,
starting at zero, which is routed to a stage by using the remainder
option.
If the data you want to partition by is not an integer, you can
explicitly hash it by calling :erlang.phash2/1
. However, note
that hash
does not guarantee an equal distribution of events
across partitions. So some partitions may be more overloaded than
others, slowing down the whole pipeline.
In the example above, we have set the same partition for all
processors and batchers. You can also specify the :partition_by
function for each "processor" and "batcher" individually.
Finally, beware of the error semantics when using partitioning. If you require ordering and a message fails, the partition will continue processing messages. Depending on the type of processing, the end result may be inconsistent. If your producer supports retrying, the failed message may be retried later, also out of order. Those issues happens regardless of Broadway and solutions to said problems almost always need to be addressed outside of Broadway too.
Telemetry
Broadway currently exposes following Telemetry events:
[:broadway, :topology, :init]
- Dispatched when the topology for a Broadway pipeline is initialized. The config key in the metadata contains the configuration options that were provided toBroadway.start_link/2
.- Measurement:
%{system_time: integer}
- Metadata:
%{supervision: pid, config: keyword}
- Measurement:
[:broadway, :processor, :start]
- Dispatched by a Broadway processor before the optionalprepare_messages/2
- Measurement:
%{system_time: integer}
- Metadata:
%{ topology_name: atom, name: atom, processor_key: atom, index: non_neg_integer, messages: [Broadway.Message.t], telemetry_span_context: reference }
- Measurement:
[:broadway, :processor, :stop]
- Dispatched by a Broadway processor afterprepare_messages/2
and after allhandle_message/3
callback has been invoked for all individual messages- Measurement:
%{duration: native_time}
- Metadata:
%{ topology_name: atom, name: atom, processor_key: atom, index: non_neg_integer, successful_messages_to_ack: [Broadway.Message.t], successful_messages_to_forward: [Broadway.Message.t], failed_messages: [Broadway.Message.t], telemetry_span_context: reference }
- Measurement:
[:broadway, :processor, :message, :start]
- Dispatched by a Broadway processor before yourhandle_message/3
callback is invoked- Measurement:
%{system_time: integer}
- Metadata:
%{ processor_key: atom, topology_name: atom, name: atom, index: non_neg_integer, message: Broadway.Message.t, telemetry_span_context: reference }
- Measurement:
[:broadway, :processor, :message, :stop]
- Dispatched by a Broadway processor after yourhandle_message/3
callback has returned- Measurement:
%{duration: native_time}
- Metadata:
%{ processor_key: atom, topology_name: atom, name: atom, index: non_neg_integer, message: Broadway.Message.t, telemetry_span_context: reference }
- Measurement:
[:broadway, :processor, :message, :exception]
- Dispatched by a Broadway processor if yourhandle_message/3
callback encounters an exception- Measurement:
%{duration: native_time}
- Metadata:
%{ processor_key: atom, topology_name: atom, name: atom, index: non_neg_integer, message: Broadway.Message.t, kind: kind, reason: reason, stacktrace: stacktrace, telemetry_span_context: reference }
- Measurement:
[:broadway, :batch_processor, :start]
- Dispatched by a Broadway batch processor before yourhandle_batch/4
callback is invoked- Measurement:
%{system_time: integer}
- Metadata:
%{ topology_name: atom, name: atom, index: non_neg_integer, messages: [Broadway.Message.t], batch_info: Broadway.BatchInfo.t, telemetry_span_context: reference }
- Measurement:
[:broadway, :batch_processor, :stop]
- Dispatched by a Broadway batch processor after yourhandle_batch/4
callback has returned- Measurement:
%{duration: native_time}
- Metadata:
%{ topology_name: atom, name: atom, index: non_neg_integer, successful_messages: [Broadway.Message.t], failed_messages: [Broadway.Message.t], batch_info: Broadway.BatchInfo.t, telemetry_span_context: reference }
- Measurement:
[:broadway, :batcher, :start]
- Dispatched by a Broadway batcher before handling events- Measurement:
%{system_time: integer}
- Metadata:
%{ topology_name: atom, name: atom, batcher_key: atom, messages: [Broadway.Message.t], telemetry_span_context: reference }
- Measurement:
[:broadway, :batcher, :stop]
- Dispatched by a Broadway batcher after handling events- Measurement:
%{duration: native_time}
- Metadata:
%{ topology_name: atom, name: atom, batcher_key: atom, telemetry_span_context: reference }
- Measurement:
Most of the events follow the :telemetry.span/3
convention for measurements.
This means that "start" events have a :system_time
representing the start of
that event using System.system_time/0
. The "stop" or "exception" events
have the duration
value, which is the difference in monotonic time between
the start and stop events.
Link to this section Summary
Callbacks
Invoked to handle generated batches.
Invoked for failed messages (if defined).
Invoked to handle/process individual messages sent from a producer.
Invoked for preparing messages before handling (if defined).
Functions
Returns all running Broadway names.
Gets the current values used for the producer rate limiting of the given pipeline.
Returns the names of producers.
Sends a list of Broadway.Message
s to the Broadway pipeline.
Starts a Broadway
process linked to the current process.
Synchronously stops the Broadway pipeline with the given reason
.
Sends a list of data as a batch of messages to the Broadway pipeline.
Sends a test message through the Broadway pipeline.
Returns the topology details for a pipeline.
Updates the producer rate limiting of the given pipeline at runtime.
Link to this section Types
Specs
Specs
Returned by start_link/2
.
Link to this section Callbacks
Specs
handle_batch( batcher :: atom(), messages :: [Broadway.Message.t()], batch_info :: Broadway.BatchInfo.t(), context :: term() ) :: [Broadway.Message.t()]
Invoked to handle generated batches.
It expects:
batcher
is the key that defined the batcher. This value can be set in thehandle_message/3
callback usingBroadway.Message.put_batcher/2
.messages
is the list ofBroadway.Message
structs in the incoming batch.batch_info
is aBroadway.BatchInfo
struct containing extra information about the incoming batch.context
is the user defined data structure passed tostart_link/2
.
It must return an updated list of messages. All messages received must be returned, otherwise an error will be logged. All messages after this step will be acknowledged according to their status.
In case of errors in this callback, the error will be logged and the whole batch will be failed. This callback also traps exits, so failures due to broken links between processes do not automatically cascade.
For more information on batching, see the "Batching" section in the Broadway
documentation.
Specs
handle_failed(messages :: [Broadway.Message.t()], context :: term()) :: [ Broadway.Message.t() ]
Invoked for failed messages (if defined).
It expects:
messages
is the list of messages that failed. If a message is failed inhandle_message/3
, this will be a list with a single message in it. If some messages are failed inhandle_batch/4
, this will be the list of failed messages.context
is the user-defined data structure passed tostart_link/2
.
This callback must return the same messages given to it, possibly updated.
For example, you could update the message data or use Broadway.Message.configure_ack/2
in a centralized place to configure how to ack the message based on the failure
reason.
This callback is optional. If present, it's called before the messages are acknowledged according to the producer. This gives you a chance to do something with the message before it's acknowledged, such as storing it in an external persistence layer or similar.
This callback is also invoked if handle_message/3
or handle_batch/4
crash or raise an error. If this callback crashes or raises an error,
the messages are failed internally by Broadway to avoid crashing the process.
Specs
handle_message( processor :: atom(), message :: Broadway.Message.t(), context :: term() ) :: Broadway.Message.t()
Invoked to handle/process individual messages sent from a producer.
It receives:
processor
is the key that defined the processor.message
is theBroadway.Message
struct to be processed.context
is the user defined data structure passed tostart_link/2
.
And it must return the (potentially) updated Broadway.Message
struct.
This is the place to do any kind of processing with the incoming message, e.g., transform the data into another data structure, call specific business logic to do calculations. Basically, any CPU bounded task that runs against a single message should be processed here.
In order to update the data after processing, use the
Broadway.Message.update_data/2
function. This way the new message can be
properly forwarded and handled by the batcher:
@impl true
def handle_message(_, message, _) do
message
|> update_data(&do_calculation_and_returns_the_new_data/1)
end
In case more than one batcher have been defined in the configuration,
you need to specify which of them the resulting message will be forwarded
to. You can do this by calling put_batcher/2
and returning the new
updated message:
@impl true
def handle_message(_, message, _) do
# Do whatever you need with the data
...
message
|> put_batcher(:s3)
end
Any message that has not been explicitly failed will be forwarded to the next step in the pipeline. If there are no extra steps, it will be automatically acknowledged.
In case of errors in this callback, the error will be logged and that particular message will be immediately acknowledged as failed, not proceeding to the next steps of the pipeline. This callback also traps exits, so failures due to broken links between processes do not automatically cascade.
Specs
prepare_messages(messages :: [Broadway.Message.t()], context :: term()) :: [ Broadway.Message.t() ]
Invoked for preparing messages before handling (if defined).
It expects:
message
is theBroadway.Message
struct to be processed.context
is the user defined data structure passed tostart_link/2
.
This is the place to prepare and preload any information that will be used
by handle_message/3
. For example, if you need to query the database,
instead of doing it once per message, you can do it on this callback.
The length of the list of messages received by this callback is based on
the min_demand
/max_demand
configuration in the processor. This callback
must always return all messages it receives, as handle_message/3
is still
called individually for each message afterwards.
Link to this section Functions
Returns all running Broadway names.
It's important to notice that no order is guaranteed.
Specs
get_rate_limiting(server :: name()) :: {:ok, rate_limiting_info} | {:error, :rate_limiting_not_enabled} when rate_limiting_info: %{ interval: non_neg_integer(), allowed_messages: non_neg_integer() }
Gets the current values used for the producer rate limiting of the given pipeline.
Returns {:ok, info}
if rate limiting is enabled for the given pipeline or
{:error, reason}
if the given pipeline doesn't have rate limiting enabled.
The returned info is a map with the following keys:
:interval
:allowed_messages
See the :rate_limiting
options in the module documentation for more information.
Examples
Broadway.get_rate_limiting(broadway)
#=> {:ok, %{allowed_messages: 2000, interval: 1000}}
Specs
Returns the names of producers.
Examples
iex> Broadway.producer_names(MyBroadway)
[MyBroadway.Producer_0, MyBroadway.Producer_1, ..., MyBroadway.Producer_7]
Specs
push_messages(broadway :: name(), messages :: [Broadway.Message.t()]) :: :ok
Sends a list of Broadway.Message
s to the Broadway pipeline.
The producer is randomly chosen among all sets of producers/stages. This is used to send out of band data to a Broadway pipeline.
Specs
Starts a Broadway
process linked to the current process.
module
is the module implementing theBroadway
behaviour.
Options
In order to set up how the pipeline created by Broadway should work,
you need to specify the blueprint of the pipeline. You can
do this by passing a set of options to start_link/2
.
Each component of the pipeline has its own set of options.
The broadway options are:
:name
- Required. Used for name registration. When an atom, all processes/stages created will be named using this value as prefix.:shutdown
- Optional. The time in milliseconds given for Broadway to gracefully shutdown without discarding events. Defaults to30_000
(ms). The default value is30000
.:max_restarts
- The default value is3
.:max_seconds
- The default value is5
.:resubscribe_interval
- The interval in milliseconds that processors wait until they resubscribe to a failed producers. Defaults to100
(ms). The default value is100
.:context
- A user defined data structure that will be passed to handle_message/3 and handle_batch/4. The default value is:context_not_set
.:producer
- Required. A keyword list of options. See "Producers options" section below. Only a single producer is allowed.:processors
- Required. A keyword list of named processors where the key is an atom as identifier and the value is another keyword list of options. See "Processors options" section below. Currently only a single processor is allowed.:batchers
- A keyword list of named batchers where the key is an atom as identifier and the value is another keyword list of options. See "Batchers options" section below. The default value is[]
.:partition_by
- A function that controls how data is partitioned across all processors and batchers. It receives aBroadway.Message
and it must return a non-negative integer, starting with zero, that will be mapped to one of the existing processors. See "Ordering and Partitioning" in the module docs for more information.:spawn_opt
- Low-level options given when starting a process. Applies to producers, processors, and batchers. Seeerlang:spawn_opt/2
for more information.:hibernate_after
- If a process does not receive any message within this interval, it will hibernate, compacting memory. Applies to producers, processors, and batchers. Defaults to15_000
(ms). The default value is15000
.
Producers options
The producer options allow users to set up the producer.
The available options are:
:module
- Required. A tuple representing a GenStage producer. The tuple format should be{mod, arg}
, wheremod
is the module that implements the GenStage behaviour andarg
the argument that will be passed to theinit/1
callback of the producer. SeeBroadway.Producer
for more information.:concurrency
- The number of concurrent producers that will be started by Broadway. Use this option to control the concurrency level of each set of producers. The default value is1
. The default value is1
.:transformer
- A tuple representing a transformer that translates a produced GenStage event into a%Broadway.Message{}
. The tuple format should be{mod, fun, opts}
and the function should have the following spec(event :: term, opts :: term) :: Broadway.Message.t
This function must be used sparingly and exclusively to convert regular messages intoBroadway.Message
. That's because a failure in the:transformer
callback will cause the whole producer to terminate, possibly leaving unacknowledged messages along the way. The default value isnil
.:spawn_opt
- Overrides the top-level:spawn_opt
.:hibernate_after
- Overrides the top-level:hibernate_after
.:rate_limiting
- A list of options to enable and configure rate limiting for producing. If this option is present, rate limiting is enabled, otherwise it isn't. Rate limiting refers to the rate at which producers will forward messages to the rest of the pipeline. The rate limiting is applied to and shared by all producers within the time limit. The following options are supported::allowed_messages
- Required. An integer that describes how many messages are allowed in the specified interval.:interval
- Required. An integer that describes the interval (in milliseconds)
during which the number of allowed messages is allowed.
If the producer produces more than allowed_messages
in interval
, only allowed_messages
will be published until
the end of interval
, and then more messages will be published.
Processors options
:concurrency
- The number of concurrent process that will be started by Broadway. Use this option to control the concurrency level of the processors. The default value isSystem.schedulers_online() * 2
.:min_demand
- Set the minimum demand of all processors stages. Default value is5
.:max_demand
- Set the maximum demand of all processors stages. Default value is10
. The default value is10
.:partition_by
- Overrides the top-level:partition_by
.:spawn_opt
- Overrides the top-level:spawn_opt
.:hibernate_after
- Overrides the top-level:hibernate_after
.
Batchers options
:concurrency
- The number of concurrent batch processors that will be started by Broadway. Use this option to control the concurrency level. Note that this only sets the numbers of batch processors for each batcher group, not the number of batchers. The number of batchers will always be one for each batcher key defined. The default value is1
. The default value is1
.:batch_size
- The size of the generated batches. Default value is100
. The default value is100
.:batch_timeout
- The time, in milliseconds, that the batcher waits before flushing the list of messages. When this timeout is reached, a new batch is generated and sent downstream, no matter if the:batch_size
has been reached or not. Default value is1000
(1 second). The default value is1000
.:partition_by
- Optional. Overrides the top-level:partition_by
.:spawn_opt
- Overrides the top-level:spawn_opt
.:hibernate_after
- Overrides the top-level:hibernate_after
.
stop(broadway, reason \\ :normal, timeout \\ :infinity)
View Source (since 0.8.0)Synchronously stops the Broadway pipeline with the given reason
.
This function returns :ok
if the server terminates with the
given reason; if it terminates with another reason, the call exits.
This function keeps OTP semantics regarding error reporting.
If the reason is any other than :normal
, :shutdown
or
{:shutdown, _}
, an error report is logged.
Specs
Sends a list of data as a batch of messages to the Broadway pipeline.
This is a convenience used for testing. Each message is automatically
wrapped in a Broadway.Message
with Broadway.CallerAcknowledger
configured to send a message back to the caller once all batches
have been fully processed.
If there are more messages in the batch than the pipeline batch_size
or if the messages in the batch take more time to process than
batch_timeout
then the caller will receive multiple messages.
It returns a reference that can be used to identify the ack messages.
See "Testing" section in module documentation for more information.
Options
:batch_mode
- when set to:flush
, the batch the message is in is immediately delivered. When set to:bulk
, batch is delivered when its size or timeout is reached. Defaults to:bulk
.:metadata
- optionally a map of additional fields to add to the message. This can be used, for example, when testingBroadwayRabbitMQ.Producer
.:acknowledger
- optionally a function that generatesack
fields of the sentBroadway.Message.t()
. This function receives the acknowledgerdata
and thefrom
field and it must return the acknowledger tuple. Seetest_message/3
for specs and examples.
Examples
For example, in your tests, you may do:
ref = Broadway.test_batch(broadway, [1, 2, 3])
assert_receive {:ack, ^ref, successful, failed}, 1000
assert length(successful) == 3
assert length(failed) == 0
Note that messages sent using this function will ignore demand and :transform
option specified in :producer option in Broadway.start_link/2
.
Specs
Sends a test message through the Broadway pipeline.
This is a convenience used for testing. The given data
is automatically wrapped in a Broadway.Message
with
Broadway.CallerAcknowledger
configured to send a message
back to the caller once the message has been fully processed.
The message is set to be flushed immediately, without waiting
for the Broadway pipeline batch_size
to be filled or the
batch_timeout
to be triggered.
It returns a reference that can be used to identify the ack messages.
See "Testing" section in module documentation for more information.
Options
:metadata
- optionally a map of additional fields to add to the message. This can be used, for example, when testingBroadwayRabbitMQ.Producer
.:acknowledger
- optionally a function that generatesack
fields of the sentBroadway.Message.t()
. This function receives the acknowledgerdata
and thefrom
field and it must return the acknowledger tuple:data :: term, from :: {pid, term} -> {module, ack_ref :: term, ack_data :: term}
Examples
For example, in your tests, you may do:
ref = Broadway.test_message(broadway, 1)
assert_receive {:ack, ^ref, [successful], []}
or if you want to override which acknowledger shall be called, you may do:
acknowledger = fn data, ack_ref -> {MyAck, ack_ref, :ok} end
Broadway.test_message(broadway, 1, acknowledger: acknowledger)
Note that messages sent using this function will ignore demand and :transform
option specified in :producer option in Broadway.start_link/2
.
Specs
topology(broadway :: name()) :: [ {atom(), [ %{ :name => atom(), optional(:concurrency) => pos_integer(), optional(:batcher_name) => atom(), optional(:batcher_key) => atom(), optional(:processor_key) => atom() } ]} ]
Returns the topology details for a pipeline.
The stages that have the "concurrency" field indicates a list of
processes running with that name prefix. Each process has "name" as
prefix plus "_" and the index of 0..(concurrency - 1)
, as atom.
For example, a producer named MyBroadway.Broadway.Producer
with
concurrency of 1 represents only a process named
MyBroadway.Broadway.Producer_0
.
Note that Broadway
does not accept multiple producers neither
multiple processors. But we choose to keep in a list for simplicity
and future proof.
Examples
iex> Broadway.topology(MyBroadway)
[
producers: [%{name: MyBroadway.Broadway.Producer, concurrency: 1}],
processors: [%{name: MyBroadway.Broadway.Processor_default, concurrency: 10, processor_key: :default}],
batchers: [
%{
batcher_name: MyBroadway.Broadway.Batcher_default,
name: MyBroadway.Broadway.BatchProcessor_default,
batcher_key: :default,
concurrency: 5
},
%{
batcher_name: MyBroadway.Broadway.Batcher_s3,
name: MyBroadway.Broadway.BatchProcessor_s3,
batcher_key: :s3,
concurrency: 3
}
]
]
Specs
update_rate_limiting(server :: name(), opts :: Keyword.t()) :: :ok | {:error, :rate_limiting_not_enabled}
Updates the producer rate limiting of the given pipeline at runtime.
Supports the following options (see the :rate_limiting
options in the module
documentation for more information):
:allowed_messages
:interval
Returns an {:error, reason}
tuple if the given broadway
pipeline doesn't
have rate limiting enabled.
Examples
Broadway.update_rate_limiting(broadway, allowed_messages: 100)