Distributed Calculator

A distributed calculator built with Microservices using go-kit, using etcd as service registry

Go-Kit architecture

- Setup
    1. Setup is done in the cmd/service 
    2. Hook all endpoints + middleware in service.go

- Request flow: client req -> handler -> endpoint -> service (logic) -> endpoint -> handler -> client res
    1. Request is received by the handler (transport specific)
    2. The transport handler will convert / deserialize the data and will call the endpoint. 
    3. Endpoint will validate the input data and will call the service 
    4. The service will contain the business logic. 

Kit CLI Commands

- Generate new services with HTTP endpoints: 
    1. # kit new service <service-name>
    2. Add functions to the service interface
    3. # kit generate service <service-name> --dmw (dmw: generate default middlewares)

- Generate new services with GRPC endpoints: 
    1 + 2 - as in HTTP service 
    3. # kit generate service <service-name> -t grpc --dmw (dmw: generate default middlewares)

- Generate Docerfile and docker compose files
    # kit generate docker - will generate a docker compose file 

- docker-compose up - will run the docker images 

- Send data to the services: 
    Calc FE: curl -s -d '{"expr": "1 + 1"}' -X POST localhost:8800/calculate
    Add service: # curl -s -d '{"numbers": [1, 2, 3]}' -X POST localhost:8800/add

gRPC / Protobuf

- Install: 
    * curl -OL https://github.com/google/protobuf/releases/download/v3.6.1/protoc-3.6.1-linux-x86_64.zip
    * unzip protoc-3.6.1-linux-x86_64.zip -d protoc3
    * sudo mv protoc3/bin/* /usr/local/bin/
    * sudo mv protoc3/include/* /usr/local/include/

- Compile 
    1. Kit will create a compile.sh in the service protobuf transport folder. 
    2. Run the compile.sh to generate the .go file from the .proto file
    3. The .go file contains: 
        3.1. The service protobuf implementation in Go. 
        3.2. Client that can speak with the gRPC service that was just created. 

External services / DB's

- etcd: 
    * Start only etcd (-d = run in the bg): # docker-compose up -d etcd 
    * Query etcd: 
        version: # curl -L http://127.0.0.1:23791/version
        get all keys: # curl -L http://127.0.0.1:23791/v2/keys/?recursive=true
        add new key: # curl http://127.0.0.1:23791/v2/keys/services/add:8081/ -X PUT -d value="add:8081"
        find by key: # curl -L http://127.0.0.1:23791/v2/keys/services/calc/
        delete a key: #  curl http://127.0.0.1:23791/v2/keys/services/v2/add:8081/ -X DELETE

- Postgres docker image run:
    docker run -it --rm -e POSTGRES_PASSWORD='' -p 5432:5432 postgres:alpine

- Redis docker image spinup:
    docker run -p "6379:6379" --rm --name dwarf-redis redis:4-alpine