Add README.md

Author: ihippik

README.md

@@ -1,2 +1,86 @@
-# lambda-go
-Serverless Computing
+# Lambda-Go
+
+This project is an attempt to understand how the most popular serverless computing solution, Lambda functions, works.
+
+It was inspired by the most popular solution, [AWS Lambda](https://aws.amazon.com/lambda/).
+
+## How it works
+
+At this stage, the project is a web server with two endpoints.
+Server port should be specified in the `APP_SERVER_PORT` environment variable.
+
+Also we need to specify logs level in the `APP_LOG_LEVEL` environment variable.
+
+For proper operation, the server must have access to the ***Docker*** daemon, 
+which is used to deploy our functions in containers.
+
+### Create function
+
+This endpoint allows us to upload an archive with Lambda function code to the server.
+
+```shell
+curl --location 'localhost:9000/lambda/{func_name}/create' \
+--form 'file=@"/func.tar.gz"'
+```
+
+To create a new Lambda function, you need to specify the function name `{func_name}` and a tar.gz archive.
+
+The archive must contain three files:
+* main.go
+* go.mod
+* go.sum
+
+The code for the application should look like the following:
+    
+```go
+package main
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+
+	"github.com/ihippik/lambda-go/lambda"
+)
+
+type Data struct {
+	Name string `json:"name"`
+}
+
+func hello(_ context.Context, data []byte) ([]byte, error) {
+	var req Data
+
+	if err := json.NewDecoder(bytes.NewReader(data)).Decode(&req); err != nil {
+		return nil, err
+	}
+
+	return []byte(fmt.Sprintf("Hello %s!", req.Name)), nil
+}
+
+func main() {
+	lambda.Start(hello)
+}
+```
+
+All handlers must have the following signature:
+
+```go
+type Handler func(ctx context.Context, payload []byte) ([]byte, error)
+```
+
+To prepare the archive, you can use the following command:
+
+```shell 
+tar -czvf func.tar.gz main.go go.mod go.sum
+```
+
+### Invoke function
+
+This endpoint allows us to run a previously uploaded function `{func_name}`
+
+```shell
+curl --location 'localhost:9000/lambda/{func_name}/invoke' \
+--header 'Content-Type: application/json' \
+--data '{"name": "Ivan"}'
+```