in aws go ssm ~ read.
Fixing AWS "not authorized to perform: ssm:GetParameter" error in Go lambda

Fixing AWS "not authorized to perform: ssm:GetParameter" error in Go lambda

So, i started to lear Go and decided to write some chat bot that for our Slack in order to ask for some routine tasks that we do during testing or development in New10. Before we were using a lot of javascript and serverless, so i took some code snippets from previous projects in order to comply with out standarts and to fasten things up.

My parameter-store policy looked like this :

parameter-store:
  PolicyName: ${self:custom.resourcePrefix}-parameter-store
  PolicyDocument:
    Version: "2012-10-17"
    Statement:
      - Effect: Allow
        Action:
          - ssm:GetParameters
        Resource:
          - arn:aws:ssm:${self:custom.region}:${self:custom.stage.infra.AWS_ACCOUNT}:parameter/handybot-service.*

I have implemented a simple function in go that would just fetch some parameter from AWS Parameter store :

func getParameter(parameterName string) (string, error) {
	region := "eu-west-1"
	sess, err := session.NewSessionWithOptions(session.Options{
		Config:            aws.Config{Region: aws.String(region)},
		SharedConfigState: session.SharedConfigEnable,
	})
	if err != nil {
		log.Fatal(err)
		return "", nil
	}

	ssmsvc := ssm.New(sess, aws.NewConfig().WithRegion(region))
	withDecryption := false
	param, err := ssmsvc.GetParameter(&ssm.GetParameterInput{
		Name:           &parameterName,
		WithDecryption: &withDecryption,
	})
	if err != nil {
		return "", err
	}
	value := *param.Parameter.Value
	return value, nil
}

so calling it from my main function would be as easy as :

value, paramStoreErr := getParameter("handybot-service.BLA")
log.Printf("parameter name is %s, %s ", value, paramStoreErr)

But, when i tried that, i got :

AccessDeniedException: User: arn:aws:sts::{aws_account_number}:assumed-role/sls-dev-handybot-LambdaRoleNoVpc/ 
sls-dev-handybot-say-hello is not authorized to perform: ssm:GetParameter on resource: arn:aws:ssm:eu-west-1:
{aws_account_number}:parameter/handybot-service.BLA status code: 400, request 
id: c299900c-5567-44b0-aa19-e1c57930e0f9: requestError null 

After checking everything multiple times, i have found this post .

It appears that you need to specificly add - ssm:GetParameter action to your policy in order for this to work. It seem that aws documentation was not clearly pointing to that. So, after i have updated my policy to this :

parameter-store:
  PolicyName: ${self:custom.resourcePrefix}-parameter-store
  PolicyDocument:
    Version: "2012-10-17"
    Statement:
      - Effect: Allow
        Action:
          - ssm:GetParameters
          - ssm:GetParameter
        Resource:
          - arn:aws:ssm:${self:custom.region}:${self:custom.stage.infra.AWS_ACCOUNT}:parameter/handybot-service.*

it all worked! I hope this will help you guys as well.

comments powered by Disqus
comments powered by Disqus