Service discovery

Example

service-discovery.py
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import logging
import aiohttp
import aiohttp.web

import asab
import asab.web
import asab.api
import asab.api.discovery
import asab.zookeeper

import os

# `instance_id`` and `service_id` are identificators set as environemnt variables.
# ASAB miroservices are meant to run in separate (Docker) containers.
os.environ["INSTANCE_ID"] = "my_application_1"

#

L = logging.getLogger(__name__)

#

asab.Config.add_defaults(
    {
        "web": {
            "listen": "0.0.0.0 8089",
        },

        "zookeeper": {
            "path": "example",
            "servers": "localhost:2181"
        },
    }
)


class MyApplication(asab.Application):

    async def initialize(self):
        # Initialize web server
        self.add_module(asab.web.Module)
        websvc = self.get_service("asab.WebService")
        self.WebContainer = asab.web.WebContainer(websvc, "web")

        # Initialize zookeeper
        self.add_module(asab.zookeeper.Module)
        self.ZooKeeperService = self.get_service("asab.ZooKeeperService")
        self.ZooKeeperContainer = asab.zookeeper.ZooKeeperContainer(self.ZooKeeperService, "zookeeper")

        # The DiscoverySession is functional only with ApiService initialized.
        self.ASABApiService = asab.api.ApiService(self)
        self.ASABApiService.initialize_web(self.WebContainer)
        self.ASABApiService.initialize_zookeeper(self.ZooKeeperContainer)

        self.DiscoveryService = self.get_service("asab.DiscoveryService")

        self.WebContainer.WebApp.router.add_get('/locate', self.locate_self)

    async def locate_self(self, request):
        # This method seeks for this application in the ZooKeeper. Thus, it calls itself, being a tiny Oroboros.
        # Try to run more than one ASAB Application with the same ZooKeeper configuration.
        # You will get a tool to locate any service in the "cluster".

        # Get config of the application:
        config = None
        async with self.DiscoveryService.session() as session:
            try:
                # use URL in format: <protocol>://<value>.<key>.asab/<endpoint> where key is "service_id" or "instance_id" and value the respective serivce identificator
                async with session.get("http://my_application_1.instance_id.asab/asab/v1/config") as resp:
                    if resp.status == 200:
                        config = await resp.json()
            except asab.api.discovery.NotDiscoveredError as e:
                L.error(e)

        if config is None:
            return aiohttp.web.json_response({"result": "FAILED"})

        return aiohttp.web.json_response(config)


if __name__ == '__main__':
    app = MyApplication()
    app.run()