Play Microservices: Scheduler service

This is the 3rd part of a series of articles under the name "Play Microservices". Links to other parts:
Part 1: Play Microservices: Bird's eye view
Part 2: Play Microservices: Authentication
Part 3: You are here
Part 4: Play Microservices: Email service
Part 5: Play Microservices: Report service
Part 6: Play Microservices: Api-gateway service
Part 7: Play Microservices: Client service
Part 8: Play Microservices: Integration via docker-compose
Part 9: Play Microservices: Security

The source code for the project can be found here:

Contents:

• Summary
• Tools
• Docker dev environment
• Database service: Mongodb
• Mongo express service
• Kafka metadata service: Zookeeper
• Zoonavigator service
• Message broker service: Kafka
• Kafka-ui service
• Scheduler-grpcui-service
• Scheduler service: Golang
• To do

• Summary

In the second part, we developed an authentication service. Now, our objective is to create a job scheduler service for our microservices application. To achieve this, we need four distinct services: a database service, a message broker service, a metadata database service dedicated to supporting the message broker, and the scheduler service itself, which is a gRPC API service. Additionally, in the development environment, we include four extra services specifically for debugging purposes. These services consist of Mongo Express, used to manage our database service, Kafkaui for managing our Kafka service, Zoonavigator for the Zookeeper service, and grpcui for testing our gRPC API.

At the end, the project directory structure will appear as follows:

• Tools

The tools required In the host machine:

• Docker: Containerization tool
• VSCode: Code editing tool
• Dev containsers extension for VSCode
• Docker extension for VSCode
• Git

The tools and technologies that we will use Inside containers for each service:

• Database service: Mongo
• Mongo express service: Mongo express
• Messaging service: Kafka
• Kafka-ui service: Kafka-ui
• Metadata service: Zookeeper
• Zoonavigator service: Zoonavigator
• grpcui service: grpcui
• Scheduler api service:
  • Golang : programming language
  • gRPC-GO: gRPC framework for golang
  • Mongo driver: Query builder for our database communication.
  • Kafka go for our message broker communications from go.
  • Quartz for scheduling purposes.

• Docker dev environment

Development inside Docker containers can provide several benefits such as consistent environments, isolated dependencies, and improved collaboration. By using Docker, development workflows can be containerized and shared with team members, allowing for consistent deployments across different machines and platforms. Developers can easily switch between different versions of dependencies and libraries without worrying about conflicts.

When developing inside a Docker container, you only need to install Docker, Visual Studio Code, and the Dev Containers and Dockerextensions on VS Code. Then you can run a container using Docker and map a host folder to a folder inside the container, then attach VSCode to the running container and start coding, and all changes will be reflected in the host folder. If you remove the images and containers, you can easily start again by recreating the container using the Dockerfile and copying the contents from the host folder to the container folder. However, it's important to note that in this case, any tools required inside the container will need to be downloaded again. Under the hood, When attaching VSCode to a running container, Visual Studio code install and run a special server inside the container which handle the sync of changes between the container and the host machine.

• Database service: Mongo

• Create a folder for the project and choose a name for it (such as 'microservice'). Then create a folder named scheduler. This folder is the root directory of current project. You can then open the root folder in VS Code by right-clicking on the folder and selecting 'Open with Code'.
• Inside the root directory create a folder with the name scheduler-db-service, then create the following files inside.
• Create a Dockerfile and set content to FROM mongo:7.0.0-rc5
• Create a file named pass.txt and set content to a password
• Create a file named user.txt and set content to admin
• Create a file named db_name.txt and set content to jobs_db
• Create a file named .env in the root directory and set the content to MONGODB_PORT=27017.
• Inside root directory create a file named docker-compose.yml and add the following content.

version: '3'
services:
# database service for scheduler service
  scheduler-db-service:
    build: 
      context: ./scheduler-db-service
      dockerfile: Dockerfile
    container_name: scheduler-db-service
    environment:
      MONGO_INITDB_ROOT_USERNAME_FILE: /run/secrets/scheduler-db-user
      MONGO_INITDB_ROOT_PASSWORD_FILE: /run/secrets/scheduler-db-pass
    env_file:
      - ./scheduler-db-service/.env
    ports:
      - ${MONGODB_PORT}:${MONGODB_PORT}
    secrets:
      - scheduler-db-user
      - scheduler-db-pass
      - scheduler-db-dbname 
    volumes:
      -  scheduler-db-service-VL:/data/db

volumes:
  scheduler-db-service-VL:

secrets:
  scheduler-db-user:
    file: scheduler-db-service/user.txt
  scheduler-db-pass:
    file: scheduler-db-service/pass.txt
  scheduler-db-dbname:
    file: scheduler-db-service/db_name.txt

• In our Docker Compose file, we use secrets to securely share credential data between containers. While we could use an .env file and environment variables, this is not considered safe. When defining secrets in the Compose file, Docker creates a file inside each container (which has the secrets name) under the /run/secrets/ path, which the containers can then read and use. For example, we will set the path of the Docker Compose secret scheduler-db-pass to the DATABASE_PASS_FILE environment variable of scheduler service. The service then will go to the path (/run/secrets/scheduler-db-pass) and read the password file. We will be using these secrets in other services later in the project.

• Mongo express service

The purpose of this service is solely for debugging and management of our running database server in the development environment.

• Inside root directory create a folder with the name mongo-express-service
• Create a Dockerfile and set content to FROM mongo-express:1.0.0-alpha.4
• Create a file named .env beside Dockerfile and set the content to

ME_CONFIG_BASICAUTH_USERNAME=admin
ME_CONFIG_BASICAUTH_PASSWORD=password123
ME_CONFIG_MONGODB_ENABLE_ADMIN=true

• Add the following lines to the .env file of the docker-compose (the .env file at the root directory of the project.)

MONGO_EXPRESS_PORT=8081

• Add the following to the service part of the docker-compose.yml.

    mongo-express:
    build:
      context: ./mongo-express-service
      dockerfile: Dockerfile
    container_name: mongo-express-service
    restart: always
    environment:
      - ME_CONFIG_MONGODB_PORT=${MONGODB_PORT}
      - ME_CONFIG_MONGODB_SERVER=scheduler-db-service
      - ME_CONFIG_MONGODB_ADMINUSERNAME=root
      - ME_CONFIG_MONGODB_ADMINPASSWORD=password123
    env_file:
      - ./mongo-express-service/.env
    ports:
      - ${MONGO_EXPRESS_PORT}:${MONGO_EXPRESS_PORT}
    depends_on:
      - scheduler-db-service

• Here, as mongo express doesn't provide a capability to read database password from the files, we simply pass mongodb credentials using environment variables (Do not forget we are in development environment).

• Now open a terminal in your project directory and run docker-compose up. Docker Compose will download and cache the required images before starting your containers. For the first run, this may take a couple of minutes. If everything goes according to plan, you can then access the mongo express panel at http://localhost:8081/ and log in using the mongo express credentials from the .env file inside the mongo-express-service container. You should see that it has successfully connected to the scheduler-db-service container.

• Now run docker-compose down

• Metadata service: Zookeeper

ZooKeeper is a centralized service for maintaining configuration information. we use it as metadata storage for our Kafka messaging service.

• Inside root directory create a folder with the name zookeeper-service
• Create a Dockerfile and set content to FROM bitnami/zookeeper:3.8.1
• Create a file named .env and set content to

ZOO_SERVER_USERS=admin,user1
# for development environment only
ALLOW_ANONYMOUS_LOGIN="yes"
# if yes, uses SASL
ZOO_ENABLE_AUTH="no" 

• Create a file named server_passwords.properties and set content to password123,password_for_user1 Please choose your own passwords.
• Add the following to the .env file of the docker-compose (the .env file at the root directory of the project.)

ZOOKEEPER_PORT=2181
ZOOKEEPER_ADMIN_CONTAINER_PORT=8078
ZOOKEEPER_ADMIN_PORT=8078

• Add the following to the service part of the docker-compose.yml.

  zk1:
    build:
      context: ./zookeeper-service
      dockerfile: Dockerfile
    container_name: zk1-service
    secrets:
      - zoo-server-pass
    env_file:
      - ./zookeeper-service/.env
    environment:
      ZOO_SERVER_ID: 1
      ZOO_SERVERS: zk1:${ZOOKEEPER_PORT}:${ZOOKEEPER_PORT} #,zk2:{ZOOKEEPER_PORT}:${ZOOKEEPER_PORT}
      ZOO_SERVER_PASSWORDS_FILE: /run/secrets/zoo-server-pass
      ZOO_ENABLE_ADMIN_SERVER: yes
      ZOO_ADMIN_SERVER_PORT_NUMBER: ${ZOOKEEPER_ADMIN_CONTAINER_PORT}
    ports:
      - '${ZOOKEEPER_PORT}:${ZOOKEEPER_PORT}'
      - '${ZOOKEEPER_ADMIN_PORT}:${ZOOKEEPER_ADMIN_CONTAINER_PORT}'
    volumes:
      - "zookeeper_data:/bitnami"

• Add the following to the secrets part of the docker-compose.yml.

  zoo-server-pass:
    file: zookeeper-service/server_passwords.properties

-ZooKeeper is a distributed application that allows us to run multiple servers simultaneously. It enables multiple clients to connect to these servers, facilitating communication between them. ZooKeeper servers collaborate to handle data and respond to requests in a coordinated manner. In this case, our zookeeper consumers (clients) are Kafka servers which is again a distributed event streaming platform. We can run multiple zookeeper services as an ensemble of zookeeper servers and attach them together via ZOO_SERVERS environment variable.

• The Bitnami ZooKeeper Docker image provides a zoo_client entrypoint, which acts as an internal client and allows us to run the zkCli.sh command-line tool to interact with the ZooKeeper server as a client. But we are going to use a GUI client for debugging purposes: Zoonavigator.

• Zoonavigator service

This service exists only in the development environment for debugging purposes. We use it to connect to zookeeper-service and manage the data.

• Inside root directory create a folder with the name zoonavigator-service
• Create a Dockerfile and set content to FROM elkozmon/zoonavigator:1.1.2
• Add ZOO_NAVIGATOR_PORT=9000 to the .env file of the docker-compose (the .env file at the root directory of the project.)
• Add the following to the service part of the docker-compose.yml.

  zoo-navigator:
    build: 
      context: ./zoonavigator-service
      dockerfile: Dockerfile
    container_name: zoo-navigator-service
    ports:
      - '${ZOO_NAVIGATOR_PORT}:${ZOO_NAVIGATOR_PORT}'
    environment:
      - CONNECTION_LOCALZK_NAME = Local-zookeeper
      - CONNECTION_LOCALZK_CONN = localhost:${ZOOKEEPER_PORT}
      - AUTO_CONNECT_CONNECTION_ID = LOCALZK
    depends_on:
      - zk1

• Now from the terminal run docker-compose up -d --build
• While running go to http://localhost:9000/. You will see the following screen:

• Enter the container name of a zookeeper service (here zk1). If everything goes according to plan, you should be able to establish a connection to the ZooKeeper service.

• No run docker-compose down. We will return to these tools later.

• Message broker service: Kafka

Apache Kafka is an open-source distributed event streaming platform that is well-suited for Microservices architecture. It is an ideal choice for implementing patterns such as event sourcing. Here We use it as an message broker for our scheduler service.

• Inside root directory create a folder with the name kafka-service
• Create a Dockerfile and set content to FROM bitnami/kafka:3.4.1
• Create a .env file beside the Docker file and set the content to:

ALLOW_PLAINTEXT_LISTENER=yes
KAFKA_ENABLE_KRAFT=no

• Add KAFKA1_PORT=9092 to the .env file of the docker-compose (the .env file at the root directory of the project.)
• Add the following to the service part of the docker-compose.yml.

  kafka1:
    build: 
      context: ./kafka-service
      dockerfile: Dockerfile
    container_name: kafka1-service
    ports:
      - '${KAFKA1_PORT}:${KAFKA1_PORT}'
    volumes:
      - "kafka_data:/bitnami"
    env_file:
      - ./kafka-service/.env
    environment:
      KAFKA_BROKER_ID: 1
      KAFKA_ADVERTISED_LISTENERS: LISTENER_DOCKER_INTERNAL://kafka1:${KAFKA1_PORT},LISTENER_DOCKER_EXTERNAL://${DOCKER_HOST_IP:-127.0.0.1}:${KAFKA1_PORT}
      KAFKA_LISTENER_SECURITY_PROTOCOL_MAP: LISTENER_DOCKER_INTERNAL:PLAINTEXT,LISTENER_DOCKER_EXTERNAL:PLAINTEXT
      KAFKA_INTER_BROKER_LISTENER_NAME: LISTENER_DOCKER_INTERNAL
      KAFKA_CFG_ZOOKEEPER_CONNECT: zk1:${ZOOKEEPER_PORT}
      KAFKA_ZOOKEEPER_PROTOCOL: PLAINTEXT #if auth is enabled in zookeeper use one of: SASL, SASL_SSL see https://hub.docker.com/r/bitnami/kafka
      KAFKA_CFG_LISTENERS: PLAINTEXT://:${KAFKA1_PORT}
    depends_on:
      - zk1

• In order to connect to our Kafka brokers for debugging purposes, we run another service. Kafka-ui.

• Kafka-ui service

This service exists only in the development environment for debugging purposes. We use it to connect to kafka-service and manage the data.

• Inside root directory create a folder with the name kafkaui-service
• Create a Dockerfile and set content to FROM provectuslabs/kafka-ui:latest
• Add KAFKAUI_PORT=8080 to the .env file of the docker-compose (the .env file at the root directory of the project.)
• Add the following to the service part of the docker-compose.yml.

  kafka-ui:
    build: 
      context: ./kafkaui-service
      dockerfile: Dockerfile
    container_name: kafka-ui-service
    restart: always
    ports:
      - ${KAFKAUI_PORT}:${KAFKAUI_PORT}
    environment:
     KAFKA_CLUSTERS_0_NAME: local
     KAFKA_CLUSTERS_0_BOOTSTRAPSERVERS: kafka1:${KAFKA1_PORT}
     DYNAMIC_CONFIG_ENABLED: 'true'
    depends_on:
      - kafka1

• Now run docker-compose run -d --build. While containers are running, go to http://localhost:8080/ to open Kafka-ui dashboard.

• From the interface, you have the ability to view and manage brokers, topics, and consumers. We'll revisit these elements in more detail shortly.
• Run docker-compose down
• Our required services are ready and running. Now it is time to Prepare development environment for our scheduler service.

• Scheduler-grpcui-service

Before commencing the development of our Scheduler service, let's incorporate an additional service into our development environment. This service will facilitate interaction with our scheduler-service for debugging purposes.

• Create a folder named grpcui-service inside scheduler folder.
• Create a Docker file and set contents to FROM fullstorydev/grpcui:v1.3.1
• Add the following to the services part of the docker-compose.yml file.

  grpcui-service:
    build:
      context: ./grpcui-service
      dockerfile: Dockerfile
    container_name: grpcui-service
    command: -port $GRPCUI_PORT -plaintext scheduler-service:${SCHEDULER_PORT}
    restart: always
    ports:
      - ${GRPCUI_PORT}:${GRPCUI_PORT}
    depends_on:
      - scheduler-service

• Add GRPCUI_PORT=5000 to compose .env file. (.env file beside docker-compose)
• We will return to this service later.

• Scheduler service: Golang

Our goal is to develop a gRPC server with Go. The typical pipeline for developing a gRPC server is quite straightforward. You define your gRPC schema inside a .proto file (see here for more info). Then you compile (Actually you transform) the .proto to your target programming language using a protocol buffer compiler tool and import it to your project. then you use a gRPC framework in your target language to run a gRPC server. This server uses .proto models in the function parameters. Next you can define corresponding database layer models and use a converter to transform between them. You receive gRPC models vis gRPC server, convert them to database models and store them in a database. In case of queries, you query the data from the database, transform them to gRPC models and return them to the user.

Here is a summary of what we are going to do: We first install protoc in our development environment. Then initialize our go project, define our proto scheme and compile it using the above tool and then run an initial gRPC server. Then we add database layer models and classes.

• Create a folder named scheduler-service inside scheduler folder.
• Create a Dockerfile inside scheduler-service and set the contents to

FROM golang:1.19

ENV PROTOC_VERSION=23.3
ENV PROTOC_ZIP=protoc-${PROTOC_VERSION}-linux-x86_64.zip
RUN apt-get update && apt-get install -y unzip
RUN curl -OL https://github.com/protocolbuffers/protobuf/releases/download/v${PROTOC_VERSION}/$PROTOC_ZIP \
    && unzip -o $PROTOC_ZIP -d /usr/local bin/protoc \
    && unzip -o $PROTOC_ZIP -d /usr/local 'include/*' \ 
    && rm -f $PROTOC_ZIP
RUN go install google.golang.org/protobuf/cmd/protoc-gen-go@latest
RUN go install google.golang.org/grpc/cmd/protoc-gen-go-grpc@latest
RUN export PATH="$PATH:$(go env GOPATH)/bin"

WORKDIR /usr/src/app

• Create a directory called "keys" within the scheduler-service folder and create a file named access_token.public.pem. Then go to here and generate an rsa 256 Key-Pair. Copy the public key to access_token.public.pem and keep the private key somewhere (We will use it later). This file acts as the public key of the auth service. Auth service generate an RSA256 key-pair and sign the JWTs with the private key. Other services verify the signature of the JWT using the public key for authentication purposes.
• Add the following to the service part of our docker-compose.yml file.

  scheduler-service:
    build: 
      context: ./scheduler-service
      dockerfile: Dockerfile
    container_name: scheduler-service
    command: sleep infinity
    environment:
      DATABASE_SCHEME: mongodb
      DATABASE_DOMAIN: scheduler-db-service
      DATABASE_PORT: ${MONGODB_PORT}
      DATABASE_USER_FILE: /run/secrets/scheduler-db-user
      DATABASE_PASS_FILE: /run/secrets/scheduler-db-pass
      DATABASE_DB_NAME_FILE: /run/secrets/scheduler-db-dbname
      KAFKA_BROKERS: kafka1-service:${KAFKA1_PORT}
      AUTH_PUBLIC_KEY_FILE: /run/secrets/auth-public-key
      # TOPICS_FILE: ''
      ENVIRONMENT: development
      SERVER_PORT: ${SCHEDULER_PORT}
    ports:
      - ${SCHEDULER_PORT}:${SCHEDULER_PORT}
    volumes:
      - ./scheduler-service:/usr/src/app
    secrets:
      - scheduler-db-user
      - scheduler-db-pass
      - scheduler-db-dbname
      - auth-public-key

...

secrets:
  # this is temorary for development environment. 
  auth-public-key:
    file: scheduler-service/keys/access_token.public.pem

• We are going to do all the development inside a docker container without installing Golang in our host machine. To do so, we run the containers and then attach VSCode to the scheduler-service container. As you may noticed, the Dockerfile for scheduler-service has no entry-point therefore we set the command value of scheduler-service to sleep infinity to keep the container awake.
• Now run docker-compose up -d --build
• While running, attach to the scheduler service by clicking bottom-left icon and then select attach to running container. Select scheduler-service and wait for a new instance of VSCode to start. At the beginning the VScode asks us to open a folder inside the container. We have selected WORKDIR /usr/src/app inside our Dockerfile, so we will open this folder inside the container. This folder is mounted to scheduler-service folder inside the host machine using docker compose volume, therefor whatever change we made will be synced to the host folder too.
• After opening the folder /usr/src/app, open a new terminal and initialize the go project by running go mod init github.com/<your_username>/play-microservices/scheduler/scheduler-service. This command will create a go.mod file.
• Run go get -u google.golang.org/grpc. This is a gRPC framework for running grpc server using Golang.
• Run go get -u google.golang.org/grpc/reflection. We add reflection to our gRPC server so that our grpcui-service can connect to it and retrieve the endpoints and messages easily for debugging purposes.
• Now create a folder named proto and create a file named job.proto inside. Set the content from here
• Run protoc --go_out=./proto --go-grpc_out=./proto proto/*.proto. This command compile our .proto file to Golang. Two files will be created. job.pb.go and job_grpc.pb.go. The first contains the proto models and the second contains the code for job service interface (We need to create our service and implement this interface).
• Note: We adopt a Golang project structure that aligns with the recommended guidelines stated here
• Create a folder named config and a file named config.go. Set the contents from here. Also create a file named .env in the same folder. we will put our internal environment variables here. Set contents from here. Create another file named .env.topics for putting kafka topics. For production environment, we pass the topics file via docker compose secrets and send the position of file via TOPICS_FILE environment variable. Then we load the contents of the file.
• Create a folder named pkg in the root directory (beside mod.go). We will put general packages here. Inside Create a folder named logger then a file named logger.go and set the contents from here.
• Create this folder tree: internal/models/job/grpc. inside grpc folder create a file named job_service.go and set the contents to

package grpc

import (
    context "context"
    proto "github.com/<your_username>/play-microservices/scheduler/scheduler-service/proto"

    codes "google.golang.org/grpc/codes"
    status "google.golang.org/grpc/status"
)

type JobService struct {
proto.UnimplementedJobsServiceServer
}

func NewJobService() *JobService {
    return &JobService{}
}

func (j *JobService) CreateJob(ctx context.Context, req *proto.CreateJobRequest) (*proto.CreateJobResponse, error) {
    return nil, status.Errorf(codes.Unimplemented, "method CreateJob not implemented")
}

func (JobService) GetJob(context.Context, *proto.GetJobRequest) (*proto.GetJobResponse, error) {
    return nil, status.Errorf(codes.Unimplemented, "method GetJob not implemented")
}

func (JobService) ListJobs(context.Context, *proto.ListJobsRequest) (*proto.ListJobsResponse, error) {
    return nil, status.Errorf(codes.Unimplemented, "method ListJobs not implemented")
}

func (JobService) UpdateJob(context.Context, *proto.UpdateJobRequest) (*proto.UpdateJobResponse, error) {
    return nil, status.Errorf(codes.Unimplemented, "method UpdateJob not implemented")
}

func (JobService) DeleteJob(context.Context, *proto.DeleteJobRequest) (*proto.DeleteJobResponse, error) {
    return nil, status.Errorf(codes.Unimplemented, "method DeleteJob not implemented")
}

• Create a folder named server inside internal folder. Then a file named server.go. set the content to

package server

import (
    "log"
    "net"

    "github.com/<your_username>/play-microservices/scheduler/scheduler-service/config"
"github.com/<your_username>/play-microservices/scheduler/scheduler-service/pkg/logger"
    MyJobGRPCService "github.com/<your_username>/play-microservices/scheduler/scheduler-service/internal/models/job/grpc"
    JobGRPCServiceProto "github.com/<your_username>/play-microservices/scheduler/scheduler-service/proto"

    "google.golang.org/grpc"
    "google.golang.org/grpc/reflection"
)

type server struct {
        log       logger.Logger
    cfg       *config.Config
}

// NewServer constructor
func NewServer(log logger.Logger, cfg *config.Config) *server {
    return &server{log: log, cfg: cfg}
}

func (s *server) Run() error {
    lis, err := net.Listen("tcp", ":"+s.cfg.ServerPort)
    if err != nil {
        log.Fatalf("failed to listen: %v", err)
    }

    grpc_server := grpc.NewServer()

    job_service := MyJobGRPCService.NewJobService()
    JobGRPCServiceProto.RegisterJobServiceServer(grpc_server, job_service)
    reflection.Register(grpc_server)

    log.Printf("server listening at %v", lis.Addr())
    if err := grpc_server.Serve(lis); err != nil {
        log.Fatalf("failed to serve: %v", err)
        return err
    }

    return nil
}

• Create a folder named cmd and a file named main.go. Set the content to

package main

import (
    "log"

    "github.com/<your_username>/play-microservices/scheduler/scheduler-service/config"
"github.com/<your_username>/play-microservices/scheduler/scheduler-service/pkg/logger"
    "github.com/<your_username>/play-microservices/scheduler/scheduler-service/internal/server"
)

func main() {

    cfg, err := config.InitConfig()
    if err != nil {
        log.Fatal(err)
    }

    appLogger := logger.NewApiLogger(cfg)
    appLogger.InitLogger()
    appLogger.Info("Starting user server")
    appLogger.Infof(
        "AppVersion: %s, LogLevel: %s, Environment: %s",
        cfg.AppVersion,
        cfg.Logger_Level,
        cfg.Environment,
    )
    appLogger.Infof("Success parsed config: %#v", cfg.AppVersion)

    s := server.NewServer(appLogger, cfg)
    s.Run()
}

• Run go mod tidy
• Run go run cmd/main.go
• While our server is running, go to docker desktop and restart grpcui-service. Now go to http://localhost:5000/. If everything goes on plan, you can connect to the server.

• Invoking any of the methods results in method xxx not implemented because we still have not implemented our job service methods.
• return to VSCode instance that is already attached to our scheduler-service. Stop the service by hitting ctl + c
• Create a file named job.go inside models folder. Inside this file we are going to define database layer models corresponding to proto models. Logic for converting from/to proto models comes here. Also we define an interface for the database of our job model and an interface for the event messaging of our job model. Set the contents of the job.go from here.

// databas interface for Job model
type JobDB interface {
    Create(ctx context.Context, job *Job) (*Job, error)
    Update(ctx context.Context, job *Job) (*Job, error)
    GetByID(ctx context.Context, jobID primitive.ObjectID) (*Job, error)
    DeleteByID(ctx context.Context, jobID primitive.ObjectID) (error)
    GetByScheduledKey(ctx context.Context, jobScheduledKey int) (*Job, error)
    DeleteByScheduledKey(ctx context.Context, jobScheduledKey int) (error)
    ListALL(ctx context.Context, pagination *utils.Pagination) (*JobsList, error)
}

//Message broker interface for Job model
type JobsProducer interface {
    PublishCreate(ctx context.Context, job *Job) error
    PublishUpdate(ctx context.Context, job *Job) error
    PublishRun(ctx context.Context, job *Job) error
}

• Create a folder named validation inside job folder. Then a file named validate.go. Set the contents from here. Inside this file we put the logic for validation of our input models.
• We have defined two interfaces for database and message broker operations. We then pass these two interfaces to our JobService model and do our logic there without knowing which database engine or messaging broker we are using. This gives us the flexibility to select whatever database (mongo or postgres) or message broker (kafka or rabitmq) we want.
• For scheduling we use this package. Run go get github.com/reugn/go-quartz/quartz
• Now change the definition of JobService inside job_service.go: Final file is here

type JobService struct {
    jobDB         models.JobDB
    jobsProducer  models.JobsProducer
    jobsScheduler scheduler.Scheduler
        proto.JobsServiceServer
}

func NewJobService(jobDB models.JobDB, jobsProducer models.JobsProducer, jobsScheduler scheduler.Scheduler) *JobService {
    return &JobService{jobDB: jobDB, jobsProducer: jobsProducer, jobsScheduler: jobsScheduler}
}

• Now it is time to select a database engine and implement JobDB interface using it. Run go get go.mongodb.org/mongo-driver. Create a folder named database inside internal/models/job folder. Then a file named job_db_mongo.go. Set the contents from here
• Create a folder named mongodb inside pkg directory and then a file named mongodb.go. This package is used to initialize our mongo db database. Set the contents from here.
• Now we select a message broker framework and implement JobsProducer interface using it. Run go get github.com/segmentio/kafka-go. Create a folder named message_broker inside internal/models/job folder. Then create a filed named job_producer_kafka.go here we implement JobsProducer interface. Set the contents from here.
• Create a folder named kafka inside pkg and then a file named kafka.go. This package is used to initialize kafka connection. Set the contents from here.
• Some notes on kafka architecture:
  • Topics: Core abstraction in kafka and represent stream of records.
  • Partitions: Topics which are a chain of records can be divided to partitions to enable parallel processing and scalability. Partitions can be distributed among brokers or reside only in one broker.
  • Brokers: Brokers are the Kafka servers that form the cluster. They store and manage the published records in a distributed manner.
  • Replication: Kafka provides replication of data for fault tolerance. Each partition can have multiple replicas spread across different brokers. Replicas ensure that if a broker fails, another broker can take over and continue serving the data seamlessly.
  • Producers: Producers are responsible for publishing data to Kafka topics.
  • Consumers: Consumers read data from Kafka topics. Consumers belongs to consumers groups. Each consumer can subscribe to multiple topics but only for one partition of a topic.
• Configuring a kafka environment can be tricky and depends on use cases.

• Now we reiterate through main.go, server.go and job_service.go files and complete the contents. Change the contents of main.go from here and server.go from here to include mongo database and kafka brokers. We initialize them inside main and pass them to the server struct.
• Add the remaining packages from pkg folder. Install the required packages via go get <packagename> command.

"github.com/pkg/errors"

• Set the contents for job_service.go from here. The code for the CreateJob function is as follows:

func (js *JobService) CreateJob(ctx context.Context, req *proto.CreateJobRequest) (*proto.CreateJobResponse, error) {
    js.log.Infof("JobService.CreateJob: grpc message arrived : %v", req)
    v := validator.CreateJobRequestValidator{CreateJobRequest: req}
    v_err := v.Validate()
    if v_err != nil {
        js.log.Errorf("JobService.CreateJob: input validation failed for request : %v with error %v", req, v_err.Error())
        return nil, status.Errorf(codes.InvalidArgument, "Invalid request body.")
    }

    job, err0 := models.JobFromProto_CreateJobRequest(req)
    if err0 != nil {
        js.log.Errorf("JobService.CreateJob: cannot create proto request")
        return nil, status.Errorf(codes.InvalidArgument, "Invalid request body.")
    }
    js.log.Infof("JobService.CreateJob: proto converted to db model : %v", job)
    job.Status = int32(proto.JobStatus_JOB_STATUS_SCHEDULED)
    jobFingerPrint := fmt.Sprintf("%s:%s:%s:%p", job.Name, job.Description, job.JobData, &job.ScheduleTime)
    job.ScheduledKey = int(fnv1a.HashString64(jobFingerPrint)) //We assume 64 bit systems!
    //store the job in the database
    js.log.Infof("JobService.CreateJob: Creating job in the database")
    created, err := js.jobDB.Create(ctx, job)
    if err != nil {
        js.log.Errorf("JobService.CreateJob: %v", err.Error())
        return nil, status.Errorf(codes.Internal, "Cannot save job. db error")
    }

    jobID := created.Id.Hex()
    js.scheduleJob(ctx, job.ScheduledKey, jobID, job.ScheduleTime)
    js.jobsProducer.PublishCreate(ctx, created)

    return &proto.CreateJobResponse{Id: jobID}, nil
}

• We receive createJob in our gRPC server. We first convert .proto model to database layer model in job := models.JobFromProto_CreateJobRequest(req). Then we set the status to SCHEDULED and save it to the database and retrieve the id. We then schedule the job and publish the topic-job-create to be consumed by other services like reports service and finally we return the CreateJobResponse to the user. Inside the schedule function, We retrieve the job from database, then set the jobState to RUNNING and save it again to the database. Then we publish topic-job-run to be consumed by our job runner service. We then listen to topic-job-run-result event which will be triggered by job runner. If the result was success we change the state of our job to COMPLETE save it to the database.

• Run go mod tidy

• Run go run cmd/main.go

• Now go to docker desktop an restart grpcui service. Then go to http://localhost:5000/. If everything goes according to plan, you can connect to the service. Select CreateJob from method name and fill in the form. For Schedule time if you pass a time before time.Now() the schedule will trigger immediately. For job data depending on the job type we need to send a specific Json string. For email type, we need to send a json with the following structure:

{
    "SourceAddress": "example@example.com",
    "DestinationAddress": "example@example.com",
    "Subject": "Message From example@example.com contact form",
    "Message": "This is a test!!!!"
}

• Push Invoke button. You will receive created job id.
• Go to http://localhost:8081/ and check the database.

• Now go to http://localhost:8080/. You can see that 3 topics have been created. The number of messages for topic-job-create and topic-job-run is 1. Because we have published topic-job-create once and topic-job-run has been published inside our scheduled function.

• Stop the service by hitting ctl + c
• A note on kafka topics creation: There are generally two common approaches for topic creation in a microservice architecture.
  • Centralized Topic Creation: a dedicated team or infrastructure administrators are responsible for creating and managing Kafka topics.
  • Self-Service Topic Creation: In this approach, each microservice is responsible for creating and managing its own Kafka topics. Here, In the development environment we follow this approach and the producer of a topic is responsible for topic creation. We define topic names in .env.topic file for development environment and load them from that file. For production environment, we can receive the file path for the topics using TOPICS_FILE environment variables (location of the file from docker compose secrets) and then load the data from it.
• We need to listen to topic-job-run results. To accomplish this we have to subscribe for topic-job-run-result topic. To accomplish that, create a file named job_consumer_kafka.go in the path internal/models/job/message_broker. Then set the contents from here.
• Add the following to server.go file.

jobsConsumer := kafka.NewJobsConsumerGroup(s.log, job_db)
jobsConsumer.Run(ctx, cancel, s.kafkaConn, s.cfg)

• Run go mod tidy then run go run cmd/main.go
• Go to http://localhost:8080/ and under consumers you can see job-run-result-consumer-scheduler which is the group id of our consumer. Now go to Topics-> topic-job-create and in the messages tab click the preview of the value of the message and copy the json structure of the message. Something like this (You need to copy yours because when listening, we search the database for job by the Id):

{
    "Id": "64c07994fcf987a39313754f",
    "Name": "n1",
    "Description": "s1",
    "ScheduleTime": "1970-01-01T00:00:00Z",
    "CreatedAt": "2023-07-26T01:40:36.888841Z",
    "UpdatedAt": "2023-07-26T01:40:36.8888412Z",
    "Status": 2,
    "JobType": 0,
    "JobData": "d1",
    "ScheduledKey": 2534671878703447000
}

• Set the value of job status of json string to 4.

• Now go to topics -> topic-job-run-result and click produce message from top right corner. Paste the json string into value and click on produce message. If everything goes according to plan, you can see the results from the terminal of VSCode. Also you can go to mongo express at http://localhost:8081/ and see that job status has changed to 4.

• Now lets add authentication to our grpc server. Create a folder named interceptors inside internal folder. then a file named auth_interceptor.go. Set the contents from here.

• Change the grpc_server creation inside server.go to match the following:

auth_interceptor := Interceptors.NewAuthInterceptor(s.log,s.cfg)
    grpc_server := grpc.NewServer(
        grpc.UnaryInterceptor(auth_interceptor.AuthInterceptor),
    )

• Run go run cmd/main.go. Now an auth interceptor in active and protect our grpc server. If you invoke any method, the response would be Missing Authorization header
• go to this site and put your generated rsa key-pairs in the corresponding boxes. Then define a simple jwt like this:

{
  "iss": "microservice-scheduler.com",
  "sub": "sheniqua",
  "aud": "maxine",
  "iat": 1689904636,
  "exp": 1689910603,
  "role": "admin"
}

• Set other configs as shown in the following image and then click the left arrow. Copy the encoded token to the clipboard.

• Now go to docker desktop and restart grpcui-service then go to http://localhost:5000/. For each request you make, set a metadata with name= authorization and the value= <token_copied>
• This time when you invoke the methods, authentication will pass. happy debugging :)

• To DO

• Add tests
• Add tracing using Jaeger
• Add monitoring and analysis using grafana
• Refactoring

I would love to hear your thoughts. Please comment on your opinions. If you found this helpful, let's stay connected on Twitter! xaledhosseini.