GoLang Tutorial - Serverless Framework (Serverless Application Model-SAM)

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Serverless Framework

The Serverless Application Model (SAM) is an open-source framework that we can use to build serverless applications.

A serverless application is a combination of Lambda functions, event sources, and other resources that work together to perform tasks. Note that a serverless application is more than just a Lambda function—it can include additional resources such as APIs, databases, and event source mappings.

Install Serverless Framework on local - Serverless CLI v1.9.0 or later:

$ npm install -g serverless
...
+ serverless@1.41.1
...

Go template

The Framework will configure AWS for Go.

There are a couple Go templates already included with the Framework as of v1.26—aws-go for a basic service with two functions, and aws-go-dep for the basic service using the dep dependency management tool. Let's try the aws-go-dep template. So, we will need dep installed. On MacOS we can install or upgrade to the latest released version with Homebrew:

$ brew install dep
Updating Homebrew...
==> Auto-updated Homebrew!
Updated 1 tap (homebrew/cask).
No changes to formulae.

==> Installing dependencies for dep: go
==> Installing dep dependency: go
==> Downloading https://homebrew.bintray.com/bottles/go-1.12.4.high_sierra.bottle.tar.gz
==> Downloading from https://akamai.bintray.com/99/9920e9264e80f0bac5098a0bbdbd1818c2c44eba37d3b9accd61c1236fcad5f2?__gda__=exp=1556574768~hmac=acc5a40c78db7c3
######################################################################## 100.0%
==> Pouring go-1.12.4.high_sierra.bottle.tar.gz
🍺  /usr/local/Cellar/go/1.12.4: 9,798 files, 452.6MB
==> Installing dep
==> Downloading https://homebrew.bintray.com/bottles/dep-0.5.1.high_sierra.bottle.tar.gz
==> Downloading from https://akamai.bintray.com/18/185d8734c3009053c1b7eca70e61e2749ca83fe3573257a95e4c7f173f8eacd8?__gda__=exp=1556574865~hmac=4db5ca163469b09
######################################################################## 100.0%
==> Pouring dep-0.5.1.high_sierra.bottle.tar.gz
🍺  /usr/local/Cellar/dep/0.5.1: 7 files, 11.5MB

$ brew upgrade dep

Make sure we're in our ${GOPATH}/src directory, then run:

$ serverless create --template aws-go-dep --path myservice
Serverless: Generating boilerplate...
Serverless: Generating boilerplate in "/Users/kihyuckhong/go/src/myservice"
 _______                             __
|   _   .-----.----.--.--.-----.----|  .-----.-----.-----.
|   |___|  -__|   _|  |  |  -__|   _|  |  -__|__ --|__ --|
|____   |_____|__|  \___/|_____|__| |__|_____|_____|_____|
|   |   |             The Serverless Application Framework
|       |                           serverless.com, v1.41.1
 -------'

Serverless: Successfully generated boilerplate for template: "aws-go-dep"

The myservice directory looks like this:

myservice
├── Gopkg.toml
├── Makefile
├── hello
│   └── main.go
├── serverless.yml
└── world
    └── main.go

Let's go into our new service directory and compile the function:

$ cd myservice

$ make
dep ensure -v
Root project is "myservice"
 2 transitively valid internal packages
 2 external packages imported from 1 projects
(0)   ✓ select (root)
(1)	? attempt github.com/aws/aws-lambda-go with 2 pkgs; 17 versions to try
(1)	    try github.com/aws/aws-lambda-go@v1.10.0
(1)	✓ select github.com/aws/aws-lambda-go@v1.10.0 w/5 pkgs
  ✓ found solution with 5 packages from 1 projects

Solver wall times by segment:
  b-source-exists: 1.425513682s
           b-gmal: 430.584962ms
      b-list-pkgs: 422.845174ms
         new-atom:   2.435891ms
      select-root:     546.41µs
          satisfy:    328.575µs
      select-atom:     127.94µs
  b-list-versions:     57.818µs
            other:     25.756µs

  TOTAL: 2.282466208s

(1/1) Wrote github.com/aws/aws-lambda-go@v1.10.0
env GOOS=linux go build -ldflags="-s -w" -o bin/hello hello/main.go
env GOOS=linux go build -ldflags="-s -w" -o bin/world world/main.go

Here is the basic directory structure (not shown all here):

The default command in the included Makefile will gather our dependencies and build the proper binaries for our functions. We can deploy now:

$ serverless deploy
Serverless: Packaging service...
Serverless: Excluding development dependencies...
Serverless: Creating Stack...
Serverless: Checking Stack create progress...
.....
Serverless: Stack create finished...
Serverless: Uploading CloudFormation file to S3...
Serverless: Uploading artifacts...
Serverless: Uploading service myservice.zip file to S3 (11.94 MB)...
Serverless: Validating template...
Serverless: Updating Stack...
Serverless: Checking Stack update progress...
................................................
Serverless: Stack update finished...
Service Information
service: myservice
stage: dev
region: us-east-1
stack: myservice-dev
resources: 16
api keys:
  None
endpoints:
  GET - https://fxmlls3d76.execute-api.us-east-1.amazonaws.com/dev/hello
  GET - https://fxmlls3d76.execute-api.us-east-1.amazonaws.com/dev/world
functions:
  hello: myservice-dev-hello
  world: myservice-dev-world
layers:
  None

If we use the two endpoints, we get the followings:

We can invoke the same from command line:

$ serverless invoke -f hello
{
    "statusCode": 200,
    "headers": {
        "Content-Type": "application/json",
        "X-MyCompany-Func-Reply": "hello-handler"
    },
    "multiValueHeaders": null,
    "body": "{\"message\":\"Go Serverless v1.0! Your function executed successfully!\"}"
}

$ serverless invoke -f world
{
    "statusCode": 200,
    "headers": {
        "Content-Type": "application/json",
        "X-MyCompany-Func-Reply": "world-handler"
    },
    "multiValueHeaders": null,
    "body": "{\"message\":\"Okay so your other function also executed successfully!\"}"
}

Here is the code: