How to get the name of the stage in an AWS Lambda function linked to API Gateway

Question

I have the following Lambda function configured in AWS Lambda :

var AWS = require('aws-sdk');
var DOC = require('dynamodb-doc');
var dynamo = new DOC.DynamoDB();
exports.handler = function(event, context) {

    var item = { id: 123,
                 foo: "bar"};

    var cb = function(err, data) {
        if(err) {
            console.log(err);
            context.fail('unable to update hit at this time' + err);
        } else {
            console.log(data);
                context.done(null, data);
        }
    };

    // This doesn't work. How do I get current stage ?
    tableName = 'my_dynamo_table_' + stage;

    dynamo.putItem({TableName:tableName, Item:item}, cb);
};

Everything works as expected (I insert an item in DynamoDB every time I call it).

I would like the dynamo table name to depend on the stage in which the lambda is deployed.

My table would be:

my_dynamo_table_staging for stage staging
my_dynamo_table_prod for stage prod

However, how do I get the name of the current stage inside the lambda ?

Edit: My Lambda is invoked by HTTP via an endpoint defined with API Gateway

Update: AWS recently rolled out a new feature called Environment Variables and Serverless Application Model (SAM). It is a built-in way to supply environment variables to your Lambda functions. (discussion here) — Benjamin Crouzier
– Benjamin Crouzier, Commented Nov 23, 2016 at 10:56

JS1010111 · Accepted Answer · 2016-11-22 23:34:44Z

19

If you have checked "Lambda Proxy Integration" in your Method Integration Request on API Gateway, you should receive the stage from API Gateway, as well as any stageVariable you have configured.

Here's an example of an event object from a Lambda function invoked by API Gateway configured with "Lambda Proxy Integration":

{
"resource": "/resourceName",
"path": "/resourceName",
"httpMethod": "POST",
"headers": {
    "header1": "value1",
    "header2": "value2"
},
"queryStringParameters": null,
"pathParameters": null,
"stageVariables": null,
"requestContext": {
    "accountId": "123",
    "resourceId": "abc",
    "stage": "dev",
    "requestId": "456",
    "identity": {
        "cognitoIdentityPoolId": null,
        "accountId": null,
        "cognitoIdentityId": null,
        "caller": null,
        "apiKey": null,
        "sourceIp": "1.1.1.1",
        "accessKey": null,
        "cognitoAuthenticationType": null,
        "cognitoAuthenticationProvider": null,
        "userArn": null,
        "userAgent": "agent",
        "user": null
    },
    "resourcePath": "/resourceName",
    "httpMethod": "POST",
    "apiId": "abc123"
},
"body": "body here",
"isBase64Encoded": false
}

edited Nov 22, 2016 at 23:34

answered Nov 22, 2016 at 22:37

JS1010111

6576 silver badges14 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

DevilCode Over a year ago

How do you access that within Lambda (java)

Benjamin Crouzier · Accepted Answer · 2016-11-23 10:52:39Z

I managed it after much fiddling. Here is a walkthrough:

I assume that you have API Gateway and Lambda configured. If not, here's a good guide. You need part-1 and part-2. You can skip the end of part-2 by clicking the newly introduced button "Enable CORS" in API Gateway

Go to API Gateway.

Click here:

Then expand Body Mapping Templates, enter application/json as content type, click the add button, then select mapping template, click edit

And paste the following content in "Mapping Template":

{
  "body" : $input.json('$'),
  "headers": {
    #foreach($param in $input.params().header.keySet())
    "$param": "$util.escapeJavaScript($input.params().header.get($param))" #if($foreach.hasNext),#end

    #end  
  },
  "stage" : "$context.stage"
}

Then click the button "Deploy API" (this is important for changes in API Gateway to take effect)

You can test by changing the Lambda function to this:

var AWS = require('aws-sdk');
var DOC = require('dynamodb-doc');
var dynamo = new DOC.DynamoDB();

exports.handler = function(event, context) {
    var currentStage = event['stage'];

    if (true || !currentStage) { // Used for debugging
        context.fail('Cannot find currentStage.' + ' stage is:'+currentStage);
        return;
    }

// ...
}

Then call your endpoint. You should have a HTTP 200 response, with the following response body:

{"errorMessage":"Cannot find currentStage. stage is:development"}

Important note:
If you have a Body Mapping Template that is too simple, like this: {"stage" : "$context.stage"}, this will override the params in the request. That's why body and headers keys are present in the Body Mapping Template. If they are not, your Lambda has not access to it.

yishaiz · Accepted Answer · 2016-09-25 18:45:59Z

4

For those who use the serverless framework it's already implemented and they can access to event.stage without any additional configurations.

See this issue for more information.

answered Sep 25, 2016 at 18:45

yishaiz

2,6234 gold badges30 silver badges54 bronze badges

Comments

Divyansh Singh · Accepted Answer · 2019-02-06 12:20:14Z

1

You can get it from event variable. I logged my event object and got this.

{  ...
    "resource": "/test"
    "stageVariables": {
        "Alias": "beta"
    }
}

answered Feb 6, 2019 at 12:20

Divyansh Singh

4016 silver badges16 bronze badges

Collectives™ on Stack Overflow

How to get the name of the stage in an AWS Lambda function linked to API Gateway

4 Answers 4

1 Comment

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

1 Comment

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related