This project is dedicated to ship a ready to use Apache Kafka / Confluent Schema Registry / Apache Avro message producing toolset by making use of the WaterDrop and AvroTurf gems. It comes as an opinionated framework which sets up solid conventions for producing messages.
Installation
Add this line to your application's Gemfile:
gem 'rimless'
And then execute:
$ bundle
Or install it yourself as:
$ gem install rimless
Usage
Configuration
You can configure the rimless gem via an Rails initializer, by environment variables or on demand. Here we show a common Rails initializer example:
Rimless.configure do |conf|
# Defaults to +Rails.env+ when available
conf.env = 'test'
# Defaults to your Rails application name when available
conf.app_name = 'your-app'
# Dito
conf.client_id = 'your-app'
# Writes to stdout by default
conf.logger = Logger.new(IO::NULL)
# Defaults to the default Rails configuration directory,
# or the current working directory plus +avro_schemas+
conf.avro_schema_path = 'config/avro_schemas'
conf.compiled_avro_schema_path = 'config/avro_schemas/compiled'
# The list of Apache Kafka brokers for cluster discovery,
# set to HAUSGOLD defaults when not set
conf.kafka_brokers = 'kafka://your.domain:9092,kafka..'
# The Confluent Schema Registry API URL,
# set to HAUSGOLD defaults when not set
conf.schema_registry_url = 'http://your.schema-registry.local'
end
The rimless gem comes with sensitive defaults as you can see. For most users an extra configuration is not needed.
Available environment variables
The rimless gem can be configured hardly with its configuration code block like shown before. Respecting the twelve-factor app concerns, the gem allows you to set almost all configurations (just the relevant ones for runtime) via environment variables. Here comes a list of available configuration options:
- KAFKA_ENV: The application environment. Falls back to
Rails.env
when available. - KAFKA_CLIENT_ID: The Apache Kafka client identifier, falls back the the local application name.
- KAFKA_BROKERS: A comma separated list of Apache Kafka brokers for cluster discovery (Plaintext, no-auth/no-SSL only for now) (eg.
kafka://your.domain:9092,kafka..
) - KAFKA_SCHEMA_REGISTRY_URL: The Confluent Schema Registry API URL to use for schema registrations.
Conventions
Apache Kafka Topic
The topic name on Kafka is prefixed with the application environment and application name. This allows the usage of a single Apache Kafka cluster for multiple application environments (eg. canary and production). The application name on the topic allows direct knowledge of the message origin. Convention rules:
- Schema is
<ENV>.<APP>.<CONCERN>
- All components are lowercase and in kebab-case form
Here comes a Kafka topic name example: production.identity-api.users
Confluent Schema Registry Subject
Each subject (schema) is versioned and named for reference on the Schema
Registry. The subject naming convention is mostly the same as the Apache Kafka
Topic convention, except the allowed characters. Apache
Avro just allows
[A-Za-z0-9_]
and no numbers on the first char. The application environment
prefix allows the usage of the very same Schema Registry instance for multipe
environments and the application name just reflects the schema origin.
Convention rules:
- Schema is
<ENV>.<APP>.<ENTITY>
- All components are lowercase and in snake_case form
Here comes a subject name example: production.identity_api.user_v1
Gotcha: Why is this user_v1
when the Schema Registry is tracking the
subject versions all by itself? At HAUSGOLD we stick to our API definition
versions of our entity representations. So a users v1 API looks like the
user_v1
schema definition, this eases interoperability. The rimless gem does
not force you to do so as well.
Organize and write schema definitions
Just because you want to produce messages with rimless, it comes to the point that you need to define your data schemas. The rimless gem supports you with some good conventions, automatic compilation of Apache Avro schema ERB templates and painless JSON validation of them.
First things first, by convention the rimless gem looks for Apache Avro schema
ERB templates on the $(pwd)/config/avro_schemas
directory. Nothing special
from the Rails perspective. You can also reconfigure the file locations, just
see the configuration
block.
Each schema template MUST end with the .avsc.erb
extension to be picked up,
even in recursive directory structures. You can make use of the ERB templating
or not, but rimless just looks for these templates. When it comes to
structuring the Avro Schemas it is important that the file path reflects the
embeded schema namespace correctly. So when $(pwd)/config/avro_schemas
is our
schema namespace root, then the production.identity_api.user_v1
schema
converts to the
$(pwd)/config/avro_schemas/compiled/production/identity_api/user_v1.avsc
file path for Apache Avro.
The corresponding Avro Schema template is located at
$(pwd)/config/avro_schemas/identity_api/user_v1.avsc.erb
. Now it's going to
be fancy. The automatic schema compiler picks up the dynamically/runtime set
namespace from the schema definition and converts it to its respective
directory structure. So when you boot your application container/instance
inside your canary environment, the schemas/messages should reflect this so
they do not mix with other environments.
Example time. $(pwd)/config/avro_schemas/identity_api/user_v1.avsc.erb:
{
"name": "user_v1",
"namespace": "<%= namespace %>",
"type": "record",
"fields": [
{
"name": "firstname",
"type": "string"
},
{
"name": "lastname",
"type": "string"
},
{
"name": "address",
"type": "<%= namespace %>.address_v1"
},
{
"name": "metadata",
"doc": "Watch out for schemaless deep hash blobs. (+.avro_schemaless_h+)",
"type": {
"type": "map",
"values": "string"
}
}
]
}
$(pwd)/config/avro_schemas/identity_api/address_v1.avsc.erb:
{
"name": "address_v1",
"namespace": "<%= namespace %>",
"type": "record",
"fields": [
{
"name": "street",
"type": "string"
}
{
"name": "city",
"type": "string"
}
]
}
The compiled Avro Schemas are written to the
$(pwd)/config/avro_schemas/compiled/
directory by default. You can
reconfigure the
location
if needed. For VCS systems like Git it is useful to create an relative ignore
list at $(pwd)/config/avro_schemas/.gitignore
with the following contents:
compiled/
Producing messages
Under the hood the rimless gem makes use of the WaterDrop gem to send messages to the Apache Kafka cluster. But with the addition to send Apache Avro encoded messages with a single call. Here comes some examples how to use it:
= { hobbies: %w(dancing singing sports) }
address = { street: 'Bahnhofstraße 5-6', city: '12305 Berlin' }
user = { firstname: 'John', lastname: 'Doe',
address: address, metadata: Rimless.avro_schemaless_h() }
# Encode and send the message to a Kafka topic (sync, blocking)
Rimless.(data: user, schema: :user_v1, topic: :users)
# schema is relative resolved to: +development.identity_api.user_v1+
# topic is relative resolved to: +development.identity-api.users+
# You can also make use of an asynchronous message sending
Rimless.(data: user, schema: :user_v1, topic: :users)
# In cases you just want the encoded Apache Avro binary blob, you can encode it
# directly with our simple helper like this:
encoded = Rimless.encode(user, schema: 'user_v1')
# Next to this wrapped shortcut (see Encoding/Decoding messages section for
# details), we provide access to our configured AvroTurf gem instance via
# +Rimless.avro+, so you can also use +Rimless.avro.encode(user, ..)+
# You can also send raw messages with the rimless gem, so encoding of your
# message must be done before
Rimless.(data: encoded, topic: :users)
# topic is relative resolved to: +development.identity-api.users+
# In case you want to send messages to a non-local application topic you can
# specify the application, too. This allows you to send a message to the
# +<ENV>.address-api.addresses+ from you local identity-api.
Rimless.(data: encoded, topic: { name: :users, app: 'address-api' })
# Also works with the Apache Avro encoding variant
Rimless.(data: user, schema: :user_v1,
topic: { name: :users, app: 'address-api' })
# And for the sake of completeness, you can also send raw
# messages asynchronously
Rimless.(data: encoded, topic: :users)
Encoding/Decoding messages
By convention we focus on the Apache Avro data format. This is provided by the AvroTurf gem and the rimless gem adds some neat helpers on top of it. Here are a few examples to show how rimless can be used to encode/decode Apache Avro data:
# Encode a data structure (no matter of symbolized, or stringified keys, or
# non-simple types) to Apache Avro format
encoded = Rimless.encode(user, schema: 'user_v1')
# Works the same for symbolized schema names
encoded = Rimless.encode(user, schema: :user_v1)
# Also supports the resolution of deep relative schemes
# (+.user.address+ becomes +<ENV>.<APP>.user.address+)
encoded = Rimless.encode(user.address, schema: '.user.address')
# Decoding Apache Avro data is even more simple. The resulting data structure
# is deeply key-symbolized.
decoded = Rimless.decode('your-avro-binary-data-here')
Handling of schemaless deep blobs
Apache Avro is by design a strict, type casted format which does not allow undefined mix and matching of deep structures. This is fine because it forces the producer to think twice about the schema definition. But sometimes there is unstructured data inside of entities. Think of a metadata hash on a user entity were the user (eg. a frontend client) just can add whatever comes to his mind for later processing. Its not searchable, its never touched by the backend, but its present.
Thats a case we're experienced and kind of solved on the rimless gem. You can
make use of the Rimless.avro_schemaless_h
method to sparsify the data
recursively. Say you have the
following metadata hash:
= {
test: true,
hobbies: %w(writing cooking moshpit),
a: {
b: [
{ c: true },
{ d: false }
]
}
}
It's messy, by design. From the Apache Avro perspective you just can define a map. The map keys are assumed to be strings - and the most hitting value data type is a string, too. Thats where hash sparsification comes in. The resulting metadata hash looks like this and can be encoded by Apache Avro:
Rimless.avro_schemaless_h()
# => {
# "test"=>"true",
# "hobbies.0"=>"writing",
# "hobbies.1"=>"cooking",
# "hobbies.2"=>"moshpit",
# "a.b.0.c"=>"true",
# "a.b.1.d"=>"false"
# }
With the help of the sparsify gem you can also revert this to its original form. But with the loss of data type correctness. Another approach can be used for these kind of scenarios: encoding the schemaless data with JSON and just set the metadata field on the Apache Avro schema to be a string. Choice is yours.
Writing tests for your messages
Producing messages is a bliss with the rimless gem, but producing code needs to be tested as well. Thats why the gem ships some RSpec helpers and matchers for this purpose. A common situation is also handled by the RSpec extension: on the test environment (eg. a continuous integration service) its not likely to have a Apache Kafka/Confluent Schema Registry cluster available. Thats why actual calls to Kafka/Schema Registry are mocked away.
First of all, just add require 'rimless/rspec'
to your spec_helper.rb
or
rails_helper.rb
.
The #avro_parse
helper is just in place to decode Apache Avro binary blobs to
their respective Ruby representations, in case you have to handle content
checks. Here comes an example:
describe 'message content' do
let(:message) { file_fixture('user_v1_avro.bin').read }
it 'contains the firstname' do
expect(avro_parse()).to include(firstname: 'John')
end
end
Nothing special, not really fancy. A more complex situation occurs when you
separate your Kafka message producing logic inside an asynchronous job (eg.
Sidekiq or ActiveJob). Therefore is the have_sent_kafka_message
matcher
available. Example time:
describe 'message producer job' do
let(:user) { create(:user) } # FactoryBot FTW
let(:action) { SendUserCreatedMessageJob.perform_now(user) }
it 'encodes the message with the correct schema' do
expect { action }.to ('test.identity_api.user_v1')
# the schema name --^
end
it 'sends a single message' do
expect { action }.to .exactly(1)
# Also available: (known from rspec-rails ActiveJob matcher)
# .at_least(2).times
# .at_most(3).times
# .exactly(:twice)
# .once
end
it 'sends the message to the correct topic' do
expect { action }.to \
.with(topic: 'test.identity-api.users')
end
it 'sends a message key' do
# Rimless.message(data: user, schema: :user_v1, topic: :users,
# key: user.id, partition: 1) # <-- additional Kafka metas
# @see https://github.com/karafka/waterdrop#usage for all options
expect { action }.to \
.with(key: String, topic: anything)
# mind the order --^
# its a argument list validation, all keys must be named
end
it 'sends the correct user data' do
expect { action }.to .with_data(firstname: 'John')
# deep hash including the given keys? --^
end
it 'sends no message (when not called)' do
expect { nil }.not_to
end
it 'allows complex expactations' do
expect { action; action }.to \
('test.identity_api.user_v1')
.with(key: user.id, topic: 'test.identity-api.users').twice
.with_data(firstname: 'John', lastname: 'Doe').twice
end
end
Development
After checking out the repo, run bin/setup
to install dependencies. Then, run
bundle exec rake spec
to run the tests. You can also run bin/console
for an
interactive prompt that will allow you to experiment.
To install this gem onto your local machine, run bundle exec rake install
. To
release a new version, update the version number in version.rb
, and then run
bundle exec rake release
, which will create a git tag for the version, push
git commits and tags, and push the .gem
file to
rubygems.org.
Contributing
Bug reports and pull requests are welcome on GitHub at https://github.com/hausgold/rimless.