# Example Extension in Go

The provided code sample demonstrates how to get a basic extension written in Go up and running. This extension can be used with runtimes that [support extensions](https://docs.aws.amazon.com/lambda/latest/dg/using-extensions.html) 

***Note:*** *This example shows an extension written in Go, not an extension running in the Go runtime. The Go 1.x runtime does not support extensions. To support extensions, you can deploy Go functions on the provided.al2 runtime. For more information, see [Migrating Lambda functions to Amazon Linux 2](http://aws.amazon.com/blogs/compute/migrating-aws-lambda-functions-to-al2/).*

## Compile package and dependencies

To run this example, you will need to ensure that your build architecture matches that of the Lambda execution environment by compiling with `GOOS=linux` and `GOARCH=amd64` if you are not running in a Linux environment.

Building and saving package into a `bin/extensions` directory:
```bash
$ cd go-example-extension
$ GOOS=linux GOARCH=amd64 go build -o bin/extensions/go-example-extension main.go
$ chmod +x bin/extensions/go-example-extension
```

## Layer Setup Process
The extensions .zip file should contain a root directory called `extensions/`, where the extension executables are located. In this sample project we must include the `go-example-extension` binary.

Creating zip package for the extension:
```bash
$ cd bin
$ zip -r extension.zip extensions/
```

Ensure that you have aws-cli v2 for the commands below.
Publish a new layer using the `extension.zip`. The output of the following command should provide you a layer arn.
```bash
aws lambda publish-layer-version \
 --layer-name "go-example-extension" \
 --region <use your region> \
 --zip-file  "fileb://extension.zip"
```
Note the LayerVersionArn that is produced in the output.
eg. `"LayerVersionArn": "arn:aws:lambda:<region>:123456789012:layer:<layerName>:1"`

Add the newly created layer version to a Lambda function.


## Function Invocation and Extension Execution

When invoking the function, you should now see log messages from the example extension similar to the following:
```
    XXXX-XX-XXTXX:XX:XX.XXX-XX:XX    EXTENSION Name: go-example-extension State: Ready Events: [INVOKE,SHUTDOWN]
    XXXX-XX-XXTXX:XX:XX.XXX-XX:XX    START RequestId: 9ca08945-de9b-46ec-adc6-3fe9ef0d2e8d Version: $LATEST
    XXXX-XX-XXTXX:XX:XX.XXX-XX:XX    [go-example-extension]  Registering...
    XXXX-XX-XXTXX:XX:XX.XXX-XX:XX    [go-example-extension]  Register response: {
                "functionName": "my-function",
                "functionVersion": "$LATEST",
                "handler": "function.handler"
        }
    XXXX-XX-XXTXX:XX:XX.XXX-XX:XX    [go-example-extension]  Waiting for event...
    XXXX-XX-XXTXX:XX:XX.XXX-XX:XX    [go-example-extension]  Received event: {
                "eventType": "INVOKE",
                "deadlineMs": 1234567890123,
                "requestId": "9ca08945-de9b-46ec-adc6-3fe9ef0d2e8d",
                "invokedFunctionArn": "arn:aws:lambda:<region>:123456789012:function:my-function",
                "tracing": {
                        "type": "X-Amzn-Trace-Id",
                        "value": "XXXXXXXXXX"
                }
        }
    XXXX-XX-XXTXX:XX:XX.XXX-XX:XX    [go-example-extension]  Waiting for event...
    ...
    ...
    Function logs...
    ...
    ...
    XXXX-XX-XXTXX:XX:XX.XXX-XX:XX    END RequestId: 9ca08945-de9b-46ec-adc6-3fe9ef0d2e8d
    XXXX-XX-XXTXX:XX:XX.XXX-XX:XX    REPORT RequestId: 9ca08945-de9b-46ec-adc6-3fe9ef0d2e8d Duration: 3.78 ms	Billed Duration: 100 ms	Memory Size: 128 MB	Max Memory Used: 59 MB	Init Duration: 264.75 ms
```