The Alchemy Micro-services Framework is a framework for creating many small interconnected services that communicate over the RabbitMQ message brokering service. Building services with Alchemy has many benefits, like:
An Alchemy service communicates by registering two queues, a service queue (shared amongst all instances of a service) and a response queue (unique to that service instance). For the purpose of clarity I will note a service with letters e.g.
B and service instances with numbers, e.g.
A1 is service
A service sends a message to another service by putting a message on its service queue (this message includes the response queue of the sender). An instance of that service will consume and process the message then respond to the received response queue. For example, if service
A1 wanted to message service
|----------| |------------|| RabbitMQ | <-- 1. Send message on queue B --------------- | Service A1 || | | || | --- 2. Consume Message from B -> |------------| | || | | Service B1 | | || | <-- 3. Respond on queue A1 -- |------------| | || | | ||----------| --- 4. Receive response on A1 ----------------> |------------|
Alchemy tries to reuse another common communication protocol, HTTP, for status codes, message formatting, headers and more. This way the basis of the messaging protocol is much simpler to explain and implement.
Passing messages between services this way means that service
A1 can send messages to
B without knowing which instance of
B will process the message. If service
B1 becomes overloaded we can see the queue build up messages, and then start a new instance of service
B, which, with zero configuration changes, immediately start processing messages.
If the instance of
B dies while processing a message, RabbitMQ will put the message back on the queue which can then be processed by another instance. This happens without the calling service knowing and so this makes the system much more resilient to errors. However, this also means that messages may be processed more than once, so implementing idempotent micro-services is very important.
Alchemy-Ether is the Node.js implementation of the Alchemy Framework. Node.js is a great environment for Alchemy as its event driven architecture reflects the Alchemy style of communication.
To install Alchemy-Ether:
npm install alchemy-ether
To create instances of two services,
B, and have instance
A1 call service
Service = require'alchemy-ether'serviceA1 = "A" # Create service instance A1serviceB1 = "B":# How service B will process the messagebody: "Hello "serviceA1startthen -> serviceB1start # Start the Servicesthen -># Service A1 sending message to BserviceA1send_request_to_service'B'body: 'Alice'thenconsolelogresponsebody # "Hello Alice"finally ->serviceA1stopthen -> serviceB1stop
This Alchemy-Ether documentation is generated with docco from its annotated source code.
The Alchemy-Ether package exports Service:
module.exports = require('./service')
2015-12-3 - Open Sourced - Graham