Friday, October 05, 2018

Oracle Fn - build your first Go function

In this guide we showcase how easy it is to build a single function using Oracle Fn based upon Go.

The first step in developing a function is to initialize a function with the fn command. Below example shows we init a new function which will be using Go as the programming language and the trigger to call the function will be a http call. We call the function myCoolFunction

[root@projectfn devstuff]# fn init --runtime go --trigger http myCoolFunction
Creating function at: /myCoolFunction
Function boilerplate generated.
func.yaml created.
[root@projectfn devstuff]#

As soon as the initalization is complete we can see that we have a new directory called myCoolFunction which has a number of files inside
[root@projectfn devstuff]# ls -la myCoolFunction/
total 16
drwxr-xr-x. 2 root root  73 Oct  5 18:48 .
drwxr-xr-x. 8 root root  90 Oct  5 18:48 ..
-rw-r--r--. 1 root root 469 Oct  5 18:48 func.go
-rw-r--r--. 1 root root 193 Oct  5 18:48 func.yaml
-rw-r--r--. 1 root root 127 Oct  5 18:48 Gopkg.toml
-rw-r--r--. 1 root root 505 Oct  5 18:48 test.json
[root@projectfn devstuff]# 

If we look at the files the two most important files are the func.go and the func.yaml file. The func.go file will contain the function logic and the func.yaml will contain the configuration of the function.

If we look at the content of func.go we can see that this is a very simple hello world example written in Go which will respond in the form of a JSON response file " Hello World" or in case you provide a JSON payload file with a name it will respond with a "Hello name". In effect the example is very simple and very handy to quickly test if your function is OK and can be used before you start coding your own logic into it.
package main

import (
 "context"
 "encoding/json"
 "fmt"
 "io"

 fdk "github.com/fnproject/fdk-go"
)

func main() {
 fdk.Handle(fdk.HandlerFunc(myHandler))
}

type Person struct {
 Name string `json:"name"`
}

func myHandler(ctx context.Context, in io.Reader, out io.Writer) {
 p := &Person{Name: "World"}
 json.NewDecoder(in).Decode(p)
 msg := struct {
  Msg string `json:"message"`
 }{
  Msg: fmt.Sprintf("Hello %s", p.Name),
 }
 json.NewEncoder(out).Encode(&msg)
}

The content of the func.yaml file will help in the configuration of the function and how it is, for example, accessible externally on what endpoint.

schema_version: 20180708
name: mycoolfunction
version: 0.0.1
runtime: go
entrypoint: ./func
format: json
triggers:
- name: mycoolfunction-trigger
  type: http
  source: 

  Now we have to build and deploy the function. What will happen in the background is that a docker container is build and that the application, the function and the trigger is registered within Fn so it can be called. As we have not defined any application name we will call this application mycoolapp. The command required and the result is shown in the example below.

[root@projectfn myCoolFunction]# fn --verbose deploy --app mycoolapp --local
Deploying mycoolfunction to app: mycoolapp
Bumped to version 0.0.4
Building image mycoolfunction:0.0.4 
FN_REGISTRY:  FN_REGISTRY is not set.
Current Context:  No context currently in use.
Sending build context to Docker daemon  6.144kB
Step 1/10 : FROM fnproject/go:dev as build-stage
 ---> fac877f7d14d
Step 2/10 : WORKDIR /function
 ---> Using cache
 ---> 910b06b938d1
Step 3/10 : RUN go get -u github.com/golang/dep/cmd/dep
 ---> Using cache
 ---> f6b396d6e1fa
Step 4/10 : ADD . /go/src/func/
 ---> 35a944c2ad0f
Step 5/10 : RUN cd /go/src/func/ && dep ensure
 ---> Running in 8ef4cfb23602
Removing intermediate container 8ef4cfb23602
 ---> 75991cccc0b0
Step 6/10 : RUN cd /go/src/func/ && go build -o func
 ---> Running in 5d38abb76d94
Removing intermediate container 5d38abb76d94
 ---> 87f20cf4d16d
Step 7/10 : FROM fnproject/go
 ---> 76aed4489768
Step 8/10 : WORKDIR /function
 ---> Using cache
 ---> 1629c0d58cc1
Step 9/10 : COPY --from=build-stage /go/src/func/func /function/
 ---> Using cache
 ---> ac97ccf6b37f
Step 10/10 : ENTRYPOINT ["./func"]
 ---> Using cache
 ---> 5c61704790e4
Successfully built 5c61704790e4
Successfully tagged mycoolfunction:0.0.4

Updating function mycoolfunction using image mycoolfunction:0.0.4...
In effect, this is the only thing you need to do to get your first function up and running. To test if it is really working we can call the function as shown below and we will get the result back as expected.
[root@projectfn myCoolFunction]# curl http://192.168.56.15:8080/t/mycoolapp/mycoolfunction-trigger
{"message":"Hello World"}

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