Pre-Req: Must have Docker for Mac installed
I wanted to play with AWS SAM to understand how it works and compare to other tech like serverless.
Install and Test SAM
Use brew to install the aws-sam-cli:
``brew upgrade
brew update
brew tap aws/tap
brew install aws-sam-cli
sam –version
SAM CLI, version 0.10.0``
Now init a go SAM project:
cd $GOPATH/src/github.com/grahamjenson/ sam init --runtime go --name hello-sam cd hello-sam
This creates a folder with:
hello-sam/ ├── Makefile <-- Make to automate build ├── README.md <-- This instructions file ├── hello-world <-- Source code for a lambda │ ├── main.go <-- Lambda function code │ └── main_test.go <-- Unit tests └── template.yaml
Install the aws-lambda-go dependency and test:
``go get github.com/aws/aws-lambda-go
go test ./…
ok github.com/grahamjenson/hello-sam/hello-world 1.041s``
Local Server
Start a HTTP server:
GOOS=linux GOARCH=amd64 go build -o hello-world/hello-world ./hello-world sam local start-api
In another terminal: ``curl http://127.0.0.1:3000/hello
Hello, 192.168.10.10``
This will pull down a docker container to execute the lambda in. This can be very slow.
Build & Deploy
SAM build and deploy is basically a wrapper around CloudFormation package and deploy commands.
package uploads relative assets from template.yaml to S3 and outputs a new file replacing them with S3 references packaged.yaml.
For this we need a S3 bucket:
aws s3 mb s3://hello-sam
Now we can use the CLI:
sam package \ --template-file template.yaml \ --output-template-file packaged.yaml \ --s3-bucket hello-sam
Specifically, sam package uploads hello-world/ to S3 and replaces its CodeUri parameter to S3 URI in packaged.yaml.
Now we can deploy:
sam deploy \ --template-file packaged.yaml \ --stack-name hello-sam \ --capabilities CAPABILITY_IAM
deploy wraps and waits to complete create-stack and update-stack.
This does not give you a chance to review what will be deployed. If you use --no-execute-changeset argument then you get a change-set ARN to use with describe-change-set and execute-change-set.
First impressions
Though I do not like CloudFormation because of its limitations (especially when compared to terraform). Being used for this use-case is great. Not having to define all the finicky little resources required for an API gateway in terraform means much less work.
The SAM CLI being used to create a local HTTP server for an API gateway is a bit clunky but works well enough. I hope they add more serverless resources like Step Functions to increase what can be tested locally.
I am now looking at past projects I should migrate over to SAM (pwnbot being the first) and future projects where I can use more advanced features like canary deploys, nested applications and web-sockets.