How do I integrate an API Gateway REST API with Amazon SQS and resolve common errors?

Resolution

You can configure API Gateway REST APIs so that they work with Amazon SQS to create an integrated solution.

Set up REST API and an Amazon SQS integration

To integrate an API Gateway REST API with Amazon SQS, follow these steps:

1.    Create an SQS queue.

2.    Create an AWS Identity and Access Management (IAM) role, and then attach an Amazon SQS policy with a SendMessage permission. This policy allows you to publish messages from the API to Amazon SQS. In the policy, replace example-region with your AWS Region, example-account-id with your AWS account ID, and example-sqs-queue-name with your SQS queue name.

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Resource": [
        "arn:aws:sqs:example-region:example-account-id:example-sqs-queue-name"
      ],
      "Action": [
        "sqs:SendMessage"
      ]
    }
  ]
}

3.    Create a REST API in API Gateway.

4.    In the API Gateway console, create an Amazon SQS integration for your newly created REST API.

• Optionally, create a REST API resource or a REST API method.
• Create a POST method.
  For Integration type, choose AWS Service.
  For AWS Region, choose your AWS Region.
  For AWS Service, choose Simple Queue Service (SQS).
  (Optional) For AWS Subdomain, enter the subdomain that the AWS service uses. Check the AWS service documentation to confirm the availability of a subdomain. For the Amazon SQS example setup, leave this blank.
  For HTTP method, choose POST.
  For Action Type, choose Use path override.
  For Path override (optional), enter your account ID and SQS queue name in the following format: example-account-id/example-sqs-queue-name. For example, 1234567890/MySQSStandardQueue.
  For Execution role, enter the ARN of the IAM role that you created in step 2.
  For Content Handling, choose the option that fits your setup.
  Clear or select Default Timeout. Choose the option that fits your setup.
  Save the new POST method.
• Continue entering your REST API integration information.
  Choose the POST method Integration Request.
  Expand HTTP Headers.
  Choose Add header.
  For Name, enter Content-Type.
  For Mapped from, enter 'application/x-www-form-urlencoded', and then choose Create.
  Expand Mapping Templates.
  For Request body passthrough, select the option that fits your requirements.
  Choose Add mapping template.
  For Content-Type, enter application/json, and then choose Create.
  For the template, enter Action=SendMessage&MessageBody=$input.body

4.    Deploy the configured REST API.

5.    Test the setup by sending the following request to API Gateway. Replace example-api-id with your API ID, example-region with your AWS Region, example-stage with your testing stage name, and example-resource with your resource name.

curl --location --request POST 'https://example-api-id.execute-api.example-region.amazonaws.com/example-stage/example-resource' \
  --header 'Content-Type: application/json' \
  --data-raw '{
    "message": "Hello World"
  }'

When your integration is successful, your response looks similar to the following:

{
  "SendMessageResponse": {
    "ResponseMetadata": {
      "RequestId": "f879fb11-e736-52c0-bd29-a0f2d09ad90d"
    },
      "SendMessageResult": {
        "MD5OfMessageAttributes": null,
        "MD5OfMessageBody": "3fc759ac1733366f98ec4270c788fcd1",
        "MD5OfMessageSystemAttributes": null,
        "MessageId": "4c360c3c-08f4-4392-bc14-8b0c88e314a2",
        "SequenceNumber": null
    }
  }
}

Resolving common errors

UnknownOperationException error

An UnknownOperationException error occurs when a user fails to configure the Content-Type as "application/x-www-form-urlencoded" in the integration request HTTP header. The UnknownOperationException error also occurs when you don't add the SendMessage action to the integration request mapping template.

AccessDenied error

The following is an example of an AccessDenied error:

{
  "Error": {
    "Code": "AccessDenied",
    "Message": "Access to the resource https://sqs.example-region.amazonaws.com/example-account-id/example-sqs-queue-name is denied.",
    "Type": "Sender"
  },
  "RequestId": "92aea8b7-47f1-5bd4-b3c4-f3d0688d3809"
}

An AccessDenied error occurs when the API integration execution role doesn’t have the sqs:SendMessage permission set to send messages to the SQS queue. The AccessDenied error can also occur when you pass special characters, such as "&" and "%", in the request body payload. You must encode the special characters to pass. Add the $util.urlEncode() function in the mapping template to convert the request body from a string to an encoded format. The following is an example mapping template:

Action=SendMessage&MessageBody=$util.urlEncode($input.body)

The following example includes the permissions that you must have to send messages to the SQS queue. Replace example-region with your AWS Region, example-account-id with your AWS account ID, and example-sqs-queue-name with your SQS queue name.

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Resource": [
        "arn:aws:sqs:example-region:example-account-id:example-sqs-queue-name"
      ],
      "Action": [
        "sqs:SendMessage"
      ]
    }
  ]
}

KMS.AccessDeniedException error

The following are two examples of KMS.AccessDeniedException errors:

{
  "Error": {
    "Code": "KMS.AccessDeniedException",
    "Message": "User: arn:aws:sts::example-account-number:assumed-role/example-sqs-queue-name/BackplaneAssumeRoleSession is not authorized to perform: kms:GenerateDataKey on resource: arn:aws:kms:example-region:example-account-number:key/example-keyId because no identity-based policy allows the kms:GenerateDataKey action (Service: AWSKMS; Status Code: 400; Error Code: AccessDeniedException; Request ID: c58f1eec-6b18-4029-826b-d05d6a715716; Proxy: null)",
    "Type": "Sender"
  },
  "RequestId": "99976a6a-3311-57e9-86e9-310d0654ff80"
}

{
  "Error": {
    "Code": "KMS.AccessDeniedException",
    "Message": "The ciphertext refers to a customer master key that does not exist, does not exist in this region, or you are not allowed to access. (Service: AWSKMS; Status Code: 400; Error Code: AccessDeniedException; Request ID: a8adea02-c246-49d9-8b3d-ff6b6a43b40f; Proxy: null)",
    "Type": "Sender"
  },
  "RequestId": "9565c451-742c-55f3-a1eb-9f3641fd30aa"
}

A KMS.AccessDeniedException error occurs when the API integration execution role can’t perform operations through AWS Key Management Service (AWS KMS). You must configure permissions to perform operations on the AWS KMS keys that are attached to the Amazon SQS server-side encrypted queue.

The following example includes the permissions that you must have to perform operations on the KMS keys that are attached to the SQS queue. Replace example-account-id with your AWS account ID, and example-api-gw-integration-execution-role with your execution role name.

{
  "Sid": "Allow use of the key",
  "Effect": "Allow",
  "Principal": {
    "AWS": "arn:aws:iam::example-account-id:role/example-api-gw-integration-execution-role"
  },
  "Action": [
    "kms:Encrypt",
    "kms:GenerateDataKey*",
    "kms:Decrypt"
  ],
  "Resource": "*"
}

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