Your First Microservice

So, let’s start developing microservices using the Pip.Services toolkit. As a simple example, we will make a Hello World microservice, which will greet you in response to your request. The communication protocol will be HTTP REST.

The microservice is structurally made up of these components:

The service, which generates responses to requests
A REST controller for the transmission of responses and requests
The component factory for the dynamic creation of components
A container process, which will be filled with the necessary components, based on a yaml file configuration.

Step 1. Environment setup

Before we can start writing-up some microservices, we’ll need to install:

Compiler and IDE

First and foremost - we’ll need a compiler for your programming language of choice, as well as some sort of code editor. In our examples, we usually use Visual Studio Code, but any fitting IDE will do.

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For working with the Go programming language, you'll need to perform its installation and setup the environment. To do this, download and install Go from their official site https://golang.org/dl/ . Select the download that corresponds to the operating system you're using, and follow the installation instructions listed on their site.

Once installed, check that the installation was completed successfully by running the following command from your console:

go version

If everything was installed successfully, the screen will display the latest version of the Go programming language.

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For working with the Python programming language, you'll need to perform its installation and setup the environment. To do this, download and install Python from their [official site](https://www.python.org/downloads/) . Select the download that corresponds to the operating system you're using, and follow the installation instructions listed on their site.

Once installed, check that the installation was completed successfully by running the following command from your console:

python --version

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Step 2. Project setup

Create a folder for the project and within it, add a requirements.txt file with the name of your microservice and a list of dependencies for your necessary components. For editing, you can use any text editor or IDE of your choice.

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go mod init quickstart

Update the generated /go.mod file to add there dependencies to Pip.Services toolkit.

/go.mod

module quickstart

go 1.22

require (
	github.com/pip-services4/pip-services4-go/pip-services4-components-go v0.0.1-2
	github.com/pip-services4/pip-services4-go/pip-services4-container-go v0.0.1-3
)

require (
	github.com/pip-services4/pip-services4-go/pip-services4-config-go v0.0.0-20240325121312-3b0195749a25 // indirect
	github.com/pip-services4/pip-services4-go/pip-services4-data-go v0.0.1-2 // indirect
	github.com/pip-services4/pip-services4-go/pip-services4-expressions-go v0.0.1-2 // indirect
	github.com/pip-services4/pip-services4-go/pip-services4-logic-go v0.0.1-3 // indirect
	github.com/pip-services4/pip-services4-go/pip-services4-observability-go v0.0.1-3 // indirect
	github.com/pip-services4/pip-services4-go/pip-services4-rpc-go v0.0.0-20240304141352-928143cb0946 // indirect
	github.com/rs/cors v1.9.0 // indirect
	goji.io v2.0.2+incompatible // indirect
	gopkg.in/yaml.v2 v2.4.0 // indirect
)

require (
	github.com/google/uuid v1.6.0 // indirect
	github.com/pip-services4/pip-services4-go/pip-services4-commons-go v0.0.1-2 // indirect
	github.com/pip-services4/pip-services4-go/pip-services4-http-go v0.0.1-4
)

In the command line execute the following command to install the dependencies:

go get -u

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The external dependencies are defined in the file below:

/requirements.txt

pip_services4_commons
pip_services4_components
pip_services4_container
pip_services4_data
pip_services4_rpc
pip_services4_http

To install these dependencies use the following command:

pip install -r requirements.txt

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Step 3. Service

The service will be a simple class that implements a single business method, which receives a name and generates a greeting. In general, business methods can call other built-in controllers or work with a database.

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func (c *HelloWorldService) Greeting(ctx context.Context, name string) (result string, err error) {
	if name == "" {
		name = c.defaultName
	}
	return "Hello, " + name + "!", nil
}

To demonstrate the dynamic configuration of a component, the recipient name will be specified by the parameter “default_name”. To get the configuration, the component must implement the interface “IConfigurable” with the method “configure”.

func (c *HelloWorldService) Configure(ctx context.Context, config *cconf.ConfigParams) {
	c.defaultName = config.GetAsStringWithDefault("default_name", c.defaultName)
}

Parameters will be read by the microservice from the configuration file and passed to the “configure” method of the corresponding component. Here’s an example of the configuration:

# Service
- descriptor: "hello-world:service:default:default:1.0"
  default_name: "World"

More details on this mechanism can be found in Component Configuration.

This is all the code of the controller in the file:

/HelloWorldService.go

package quickstart

import (
	"context"

	cconf "github.com/pip-services4/pip-services4-go/pip-services4-components-go/config"
)

type HelloWorldService struct {
	defaultName string
}

func NewHelloWorldService() *HelloWorldService {
	c := HelloWorldService{}
	c.defaultName = "Pip User"
	return &c
}

func (c *HelloWorldService) Configure(ctx context.Context, config *cconf.ConfigParams) {
	c.defaultName = config.GetAsStringWithDefault("default_name", c.defaultName)
}

func (c *HelloWorldService) Greeting(ctx context.Context, name string) (result string, err error) {
	if name == "" {
		name = c.defaultName
	}
	return "Hello, " + name + "!", nil
}

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def greeting(name):        
    return f"Hello, {name if name is not None else self.__defaultName} !"

To demonstrate the dynamic configuration of a component, the recipient name will be specified by the parameter “__default_name”. To get the configuration, the component must implement the interface “IConfigurable” with the method “configure”.

def configure(config):        
    self.__default_name = config.get_as_string_with_default("default_name", self.__default_name)

Parameters will be read by the microservice from the configuration file and passed to the “configure” method of the corresponding component. Here’s an example of the configuration:

# Service
- descriptor: "hello-world:service:default:default:1.0"
  default_name: "World"

More details on this mechanism can be found in Component Configuration.

This is all the code of the controller in the file:

/HelloWorldService.py

# -*- coding: utf-8 -*- 
class HelloWorldService:
    __default_name = None

    def __init__(self):
        self.__default_name = "Pip User"

    def configure(config):
        self.__default_name = config.get_as_string_with_default("default_name", self.__default_name)

    def greeting(name):
        return f"Hello, {name if name is not None else self.__default_name} !"

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Step 4. REST controller

One of the most popular ways of transferring data between microservices is using the synchronous HTTP REST protocol. The HelloWorldRestController will be used to implement an external REST interface. This component extends the abstract RestController of the Pip.Services toolkit, which implements all the necessary functionality for processing REST HTTP requests.

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type HelloWorldRestController struct {
	*rpc.RestController
	service *HelloWorldService
}

Next, we’ll need to register the REST operations that we’ll be using in the class’s Register method. In this microservice, we’ll only be needing to implement a single GET command: “/greeting”. This command receives a “name” parameter, calls the service’s “greeting” method, and returns the generated result to the client.

func (c *HelloWorldRestController) greeting(res http.ResponseWriter, req *http.Request) {
	name := req.URL.Query().Get("name")
	result, err := c.service.Greeting(req.Context(), name)
	c.SendResult(res, req, result, err)
}

func (c *HelloWorldRestController) Register() {
	c.RegisterRoute("get", "/greeting", nil, c.greeting)
}

To get a reference to the service, add its handle to the DependencyResolver under the name “service”. And for the registration mechanism to work correctly, you must pass a pointer to RestService on the component that implements the IRegistrable interface. Let’s do it in the component constructing method:

func NewHelloWorldRestController() *HelloWorldRestController {
	c := &HelloWorldRestController{}
	c.RestController = rpc.InheritRestController(c)
	c.BaseRoute = "/hello_world"
	c.DependencyResolver.Put(context.Background(), "service", cref.NewDescriptor("hello-world", "service", "*", "*", "1.0"))
	return c
}

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class HelloWorldRestController(RestController):

Next, we’ll need to register the REST operations that we’ll be using in the class’s register method. In this microservice, we’ll only be needing to implement a single GET command: “/greeting”. This command receives a “name” parameter, calls the service’s “greeting” method, and returns the generated result to the client.

def register(self):
    self.register_route(method="GET", route=self._route, handler=self.greeting)


def greeting(self, name):
    result = Parameters.from_tuples("name", self._controller.greeting(name))

    self.send_result(result)

To get a reference to the service, we’ll add its descriptor to the _dependency_resolver with a name of “service”.

def __init__(self):
    super(HelloWorldRestService, self).__init__()
    self._route = "/hello_world"
    ServiceDescriptor = Descriptor('hello-world', 'service', '*', '*', '1.0')
    self._dependency_resolver.put('service', ServiceDescriptor)

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Using this descriptor, the base class will be able to find a reference to the service during component linking. Check out The Locator Pattern for more on how this mechanism works.

We also need to set a base route in the controller’s constructor using the _base_route property. As a result, the microservice’s full REST request will look something like:

GET /hello_world/greeting?name=John

Full listing for the REST controller can be found in the following file:

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/HelloWorldRestController.go

package quickstart

import (
	"context"
	"net/http"

	cref "github.com/pip-services4/pip-services4-go/pip-services4-components-go/refer"
	rpc "github.com/pip-services4/pip-services4-go/pip-services4-http-go/controllers"
)

type HelloWorldRestController struct {
	*rpc.RestController
	service *HelloWorldService
}

func NewHelloWorldRestController() *HelloWorldRestController {
	c := &HelloWorldRestController{}
	c.RestController = rpc.InheritRestController(c)
	c.BaseRoute = "/hello_world"
	c.DependencyResolver.Put(context.Background(), "service", cref.NewDescriptor("hello-world", "service", "*", "*", "1.0"))
	return c
}

func (c *HelloWorldRestController) SetReferences(ctx context.Context, references cref.IReferences) {
	c.RestController.SetReferences(ctx, references)
	depRes, depErr := c.DependencyResolver.GetOneRequired("service")
	if depErr == nil && depRes != nil {
		c.service = depRes.(*HelloWorldService)
	}
}

func (c *HelloWorldRestController) greeting(res http.ResponseWriter, req *http.Request) {
	name := req.URL.Query().Get("name")
	result, err := c.service.Greeting(req.Context(), name)
	c.SendResult(res, req, result, err)
}

func (c *HelloWorldRestController) Register() {
	c.RegisterRoute("get", "/greeting", nil, c.greeting)
}

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/HelloWorldRestController.py

class HelloWorldRestController(RestController):

    def __init__(self):
        super(HelloWorldRestController, self).__init__()
        self._route = "/hello_word"
        SeriveDescriptor = Descriptor('hello-world', 'service', '*', '*', '1.0')
        self._dependency_resolver.put('controller', ControllerDescriptor)

    def set_references(self, references):
        super(HelloWorldRestController, self).set_references(references)
        self._servicer = self._dependency_resolver.get_one_required('service')

    def register(self):
        self.register_route(method="GET", route=self._route, handler=self.greeting, schema=None)

    def greeting(self, name):
        result = self._service.greeting(name)
        self.send_result(result)

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Step 5. Component factory

When a microservice is being populated by components based on the configuration being used, it requires a special factory to create components in accordance with their descriptors. The HelloWorldControllerFactory class is used for just that, as it extends the Factory class of the Pip.Services toolkit.

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type HelloWorldControllerFactory struct {
	*cbuild.Factory
}

Next, in the factory’s constructor, we’ll be registering descriptors and their corresponding component types.

func NewHelloWorldControllerFactory() *HelloWorldControllerFactory {
	c := HelloWorldControllerFactory{}
	c.Factory = cbuild.NewFactory()
	c.RegisterType(
		cref.NewDescriptor("hello-world", "service", "default", "*", "1.0"),
		NewHelloWorldService,
	)
	c.RegisterType(
		cref.NewDescriptor("hello-world", "controller", "http", "*", "1.0"),
		NewHelloWorldRestController,
	)
	return &c
}

For more info on how this works, be sure to check out Process Container.

Full listing of the factory’s code found in the file:

‍/HelloWorldControllerFactory.go

package quickstart

import (
	cbuild "github.com/pip-services4/pip-services4-go/pip-services4-components-go/build"
	cref "github.com/pip-services4/pip-services4-go/pip-services4-components-go/refer"
)

type HelloWorldControllerFactory struct {
	*cbuild.Factory
}

func NewHelloWorldControllerFactory() *HelloWorldControllerFactory {
	c := HelloWorldControllerFactory{}
	c.Factory = cbuild.NewFactory()
	c.RegisterType(
		cref.NewDescriptor("hello-world", "service", "default", "*", "1.0"),
		NewHelloWorldService,
	)
	c.RegisterType(
		cref.NewDescriptor("hello-world", "controller", "http", "*", "1.0"),
		NewHelloWorldRestController,
	)
	return &c
}

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class HelloWorldControllerFactory(Factory):

Next, in the factory’s constructor, we’ll be registering descriptors and their corresponding component types.

def __init__(self):
    super(HelloWorldControllerFactory, self).__init__()
    ServiceDescriptor = Descriptor('hello-world', 'service', 'default', '*', '1.0')
    HttpControllerDescriptor = Descriptor('hello-world', 'controller', 'http', '*', '1.0')
    self.register_as_type(ServiceDescriptor, HelloWorldService)
    self.register_as_type(HttpControllerDescriptor, HelloWorldRestController)

For more info on how this works, be sure to check out Process Container.

A full listing of the factory’s code can be found in the file:

‍/HelloWorldServiceFactory.py

# -*- coding: utf-8 -*- 
from HelloWorldService import HelloWorldService
from HelloWorldRestController import HelloWorldRestController
from pip_services4_components.refer import Descriptor
from pip_services4_components.build import Factory


class HelloWorldControllerFactory(Factory):
    def __init__(self):

        super(HelloWorldControllerFactory, self).__init__()
        ServiceDescriptor = Descriptor('hello-world', 'service', 'default', '*', '1.0')
        HttpControllerDescriptor = Descriptor('hello-world', 'controller', 'http', '*', '1.0')
        self.register_as_type(ServiceDescriptor, HelloWorldService)
        self.register_as_type(HttpControllerDescriptor, HelloWorldRestController)

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Step 6. Container

Last but not least, our microservice needs a container component. This component creates all of the other components, links them with one another, and controls their life cycle. Although there exist many different ways of running a microservice in a container (regular classes, serverless functions, serlets, etc), we’ll be running our example microservice as a system process. To do this, we’ll make the HelloWorldProcess extend the ProcessContainer class of the Pip.Services toolkit.

Although containers can be populated by components manually, we’ll be using dynamic configuration to do this. By default, ProcessContainer reads the configuration from an external config.yaml file. All we have left to do is register the factory for creating components from their descriptors.

The full listing of the container’s code can be found in the file:

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‍/HelloWorldProcess.go

package quickstart

import (
	cproc "github.com/pip-services4/pip-services4-go/pip-services4-container-go/container"
	rbuild "github.com/pip-services4/pip-services4-go/pip-services4-http-go/build"
)

type HelloWorldProcess struct {
	*cproc.ProcessContainer
}

func NewHelloWorldProcess() *HelloWorldProcess {
	c := HelloWorldProcess{}
	c.ProcessContainer = cproc.NewProcessContainer("hello-world", "HelloWorld microservice")
	c.SetConfigPath("./config.yaml")
	c.AddFactory(NewHelloWorldControllerFactory())
	c.AddFactory(rbuild.NewDefaultHttpFactory())
	return &c
}

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/HelloWorldProcess.py

# -*- coding: utf-8 -*- 
from HelloWorldControllerFactory import HelloWorldControllerFactory
from pip_services4_container.container import ProcessContainer
from pip_services4_http.build import DefaultRpcFactory


class HelloWorldProcess(ProcessContainer):
    def __init__(self):

        super(HelloWorldProcess, self).__init__('hello-world', 'HelloWorld microservice')
        self._config_path = './config.yaml'
        self._factories.add(HelloWorldControllerFactory())
        self._factories.add(DefaultRpcFactory())

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The dynamic configuration is defined in the file:

‍/config.yaml

---
---
# Container context
- descriptor: "pip-services:context-info:default:default:1.0"
  name: "hello-world"
  description: "HelloWorld microservice"
   
# Console logger
- descriptor: "pip-services:logger:console:default:1.0"
  level: "trace"
   
# Performance counter that post values to log
- descriptor: "pip-services:counters:log:default:1.0"
   
# Service
- descriptor: "hello-world:service:default:default:1.0"
  default_name: "World"
   
# Shared HTTP Endpoint
- descriptor: "pip-services:endpoint:http:default:1.0"
  connection:
    protocol: http
    host: 0.0.0.0
    port: 8080
   
    # HTTP controller V1
- descriptor: "hello-world:controller:http:default:1.0"
   
# Heartbeat controller
- descriptor: "pip-services:heartbeat-controller:http:default:1.0"
   
# Status controller
- descriptor: "pip-services:status-controller:http:default:1.0"

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Looking at the configuration file, we can conclude that the following components will be created in the microservice:

ContextInfo - standard Pip.Services component for determining the name and description of a microservice.
ConsoleLogger - standard Pip.Services component for writing logs to stdout,
LogCounters - standard Pip.Services component for logging performance counters.
HelloWorldService - the service of our microservice, implemented in step 2. Make note of the service’s descriptor, as it will be used to link the service class to the REST controller.
HttpEndpoint - standard Pip.Services component that allows multiple services to use a single HTTP port simultaneously.
HelloWorldRestController - the REST controller we implemented on step 3.
HeartbeatRestController - standard Pip.Services component that is used to check whether or not a microservice is still up and running by calling GET /heartbeat.
StatusRestController - standard Pip.Services component for getting the status of a microservice by calling GET /status.

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Looking at the configuration file, we can conclude that the following components will be created in the microservice:

ContextInfo - standard Pip.Services component for determining the name and description of a microservice.
ConsoleLogger - standard Pip.Services component for writing logs to stdout,
LogCounters - standard Pip.Services component for logging performance counters.
HelloWorldController - the controller of our microservice, implemented in step 2. Make note of the controller’s descriptor, as it will be used to link the controller class to the REST service.
HttpEndpoint - standard Pip.Services component that allows multiple services to use a single HTTP port simultaneously.
HelloWorldRestServices - the REST service we implemented on step 3.
HeartbeatRestController - standard Pip.Services component that is used to check whether or not a microservice is still up and running by calling GET /heartbeat.
StatusRestController - standard Pip.Services component for getting the status of a microservice by calling GET /status.

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As you may have noticed, more than half of the components are being taken from Pip.Services and used “right out of the box”. This significantly expands our microservice’s capabilities, with minimal effort on our part.

Step 7. Run and test the microservice

We’ll need a special file to run the microservice. All this file does is creates a container instance and runs it with the parameters provided from the command line.

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/bin/main.go

package main

import (
	"context"
	"os"
	"quickstart"
)

func main() {
	proc := quickstart.NewHelloWorldProcess()
	proc.Run(context.Background(), os.Args)
}

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/main.py


# -*- coding: utf-8 -*- 
from HelloWorldProcess import HelloWorldProcess

if __name__ == '__main__':
    runner = HelloWorldProcess()
    print("run")
    try:
        runner.run()
    except Exception as ex:
        print(ex)

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When a microservice starts up, the following sequence of events takes place:

A container is created and started;
The container reads the configuration found in config.yaml;
Using the factory, the container creates the necessary components in accordance with their descriptors (see Process Container);
The components are configured. During this step, all components that implement the IConfigurable interface have their configure methods called with the configuration defined in config.yaml passed as a parameter (see Component Configuration);
Components are linked. All components that implement the IReferenceable interface get their setReferences methods called with a list of components available in the container. With the help of descriptors, objects can find all necessary dependencies (see The Component References);
Components with active processes are run. A component is considered to contain active processes if it implements the IOpenable interface and has an open method defined (see The Component Lifecycle).

When the microservice receives a signal to stop the process, the reverse sequence takes place:

Components with active processes are closed - classes implementing the IClosable interface get their close methods called; Components are unlinked. All components that implement the IUnreferenceable interface have their unsetReferences methods called;
The components previously created in the container are destroyed;
The container is stopped.

To start the microservice, run the following command from a terminal:

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go run ./bin/run.go

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python ./run.py

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If the microservice started up successfully, you should see the following result in the terminal:

[echo:INFO:2024-04-26T15:15:30.284Z] Press Control-C to stop the microservice...
[echo:DEBUG:2024-04-26T15:15:30.542Z] Opened REST service at http://0.0.0.0:8080
[echo:INFO:2024-04-26T15:15:30.542Z] Container hello-world started.

Test the microservice by requesting the following URL in a browser:

http://localhost:8080/hello_world/greeting?name=John

If all’s well, you should get the following string as a result:

Hello, John!

All source codes are available on GitHub.

To learn even more about Pip.Services, consider creating a Data Microservice as your next step!