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Invoke a Lambda function asynchronously from API Gateway

How can I invoke a Lambda function asynchronously from my Amazon API Gateway API?

Last updated: 2022-12-12

I want to invoke an AWS Lambda function asynchronously instead of synchronously for my Amazon API Gateway API.

Resolution

REST APIs

In Lambda non-proxy integration, the backend Lambda function is invoked synchronously by default. You can configure the Lambda function for a Lambda non-proxy integration to be invoked asynchronously by specifying 'Event' as the Lambda invocation type.

1.    Open the API Gateway console, choose APIs , and then choose your REST API.

2.    In Resources , choose GET , and then choose Integration Request .

3.    In Integration type , choose Lambda Function .

4.    Expand HTTP Headers , and then choose Add header .

5.    For Name , enter X-Amz-Invocation-Type .

6.    For Mapped from , enter 'Event' .

7.    Redeploy the REST API.

To invoke the Lambda function with the option for either asynchronous or synchronous, add an InvocationType header.

1.    Open the API Gateway console, choose APIs , and then choose your REST API.

2.    In Resources , choose GET , and then choose Method Request .

3.    In Request Validator , choose the edit icon, choose the dropdown list, and then choose Validate query string parameters and headers .

4.    Choose the update icon to save changes.

5.    Expand HTTP Headers , and then choose Add header .

6.    For Name , enter InvocationType , and then choose Required .

7.    In Integration Request , Expand HTTP Headers , and then choose Add header .

8.    For Name , enter X-Amz-Invocation-Type .

9.     For Mapped from , enter method.request.header.InvocationType .

10.    Redeploy the REST API.

Clients can include the InvocationType: Event header in API requests for asynchronous invocations or InvocationType: RequestResponse for synchronous invocations.

For more information, see Set up asynchronous invocation of the backend Lambda function.

HTTP APIs

HTTP APIs only support proxy integrations for Lambda. You can't set the X-Amz-Invocation-Type header in the API Gateway integration for HTTP APIs. You can use two Lambda functions with one acting as proxy.

Example configuration:

HTTP API --> Invoke Lambda1 synchronously --> Invoke Lambda2 asynchronously

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Troubleshoot high latency in API Gateway requests

How do I troubleshoot high latency in my API Gateway requests that are integrated with Lambda?

Last updated: 2022-12-08

Response times are slow when I make requests to an Amazon API Gateway API that’s integrated with an AWS Lambda function. How do I determine the cause of high latency?

Resolution

High latency must be addressed when an API endpoint that’s integrated with a Lambda function takes too long to send responses to a client. Review the metrics for API Gateway to identify the section of the request/response flow that’s causing high latency. After you determine the cause of high latency, you can work to reduce the delays.

Filter CloudWatch metrics to review latency metrics on the API

To identify the section of the request/response flow that’s causing high latency, first perform the following steps:

  1. Observe the latency of the client after sending a request to the API.
  2. After you note the overall latency, open the Amazon CloudWatch console. In the left navigation pane, choose Metrics , All metrics . In the metrics search box, enter APIGateway . From the search results, choose API Gateway , ApiId .
  3. In the list of APIs, filter for the specified API by using the API ID or the API name. After filtering, check the IntegrationLatency and Latency check boxes.
    Note: The API ID and API name are available from the API Gateway console.
  4. Open the Graphed metrics tab. For Statistic , choose Maximum . For Period , choose 1 minute . Above the graph, select the Custom time period. Choose the time frame during which the client experienced high latency.
  5. Review both the IntegrationLatency and Latency metrics. Note the values and timestamps when these metrics have high values. The values can explain the cause for high latency.

Compare metrics to identify the cause of high latency

Continue to review the metrics related to the request/response flow to find the cause of high latency:

  1. Compare the API Gateway Latency metric to the overall latency value observed at the client.
    For example, an API has a Latency metric with a Maximum value that’s approximately equal to the Max Latency value at the client. These values suggest that the maximum delay in the request/response flow is the time taken by API Gateway to process requests. API Gateway processing time includes the time taken to send requests to Lambda, wait for responses from Lambda, and send responses to a client.
  2. Compare the IntegrationLatency metric with the Latency metric for the API.
    For example, the IntegrationLatency metric is approximately equal to the Latency metric. These values indicate that latency at the API is primarily caused by backend requests sent to Lambda that are taking longer to respond. The IntegrationLatency metric includes the time between API Gateway sending a request and API Gateway receiving a response from the backend
  3. When the IntegrationLatency metric is low when compared to the Latency metric for the API, the backend response times are low. In this scenario, it takes longer to process the API requests or responses.
    For example, mapping templates configured in the API or an API Gateway Lambda authorizer both might create delays.
  4. When the Latency metric for the API is much lower than the latency observed at the client, the route might be causing delays. Review the route between the client and API Gateway to confirm whether there are any intermediate endpoints that are adding delays.
    For example, private VPN connections or proxies might create delays.

View Lambda metrics to identify the cause of high IntegrationLatency

Finally, focus on the Lambda metrics related to the request/response flow to find the cause of high IntegrationLatency :

  1. Check the Lambda function Duration metric to confirm whether the Lambda function’s execution time is longer. If the Lambda function’s execution time has increased, review the CloudWatch log to find the section of code that’s causing high latency. By default, Lambda functions log the START, END, and REPORT statements in CloudWatch logs. Add custom log statements at each logical section of the Lambda function code to get verbose CloudWatch logs.
  2. If the Duration metric didn't change during the period of high latency at the client, determine if the initialization time increased. Initialization time in a Lambda function is the time taken to set up the execution environment to process a request. Requests that come from API Gateway might require a new environment for processing. This is set up through Lambda. Typically, the code that’s present outside the Lambda function handler runs during the initialization time. Code that takes longer to complete can cause delays for the overall response times to the client.
    Note : Initialization time is known as INIT or cold start.
  3. Confirm whether there’s any increase in the initialization time’s Duration by verifying the report statements in the Lambda function logs. Initialization time that's high for some requests can cause an increase in the IntegrationLatency metric for API Gateway.

Working with metrics for HTTP APIs

Amazon API Gateway dimensions and metrics

Monitoring WebSocket API execution with CloudWatch metrics

Viewing metrics on the CloudWatch console

Lambda runtime environment lifecycle

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Troubleshoot API Gateway logs

How can I use Amazon API Gateway logs for troubleshooting?

Last updated: 2022-12-07

I want to use Amazon API Gateway logs for troubleshooting API issues.

Short description

To troubleshoot an API Gateway REST API or WebSocket API, turn on execution logging and access logging using Amazon CloudWatch Logs. Make sure that you have attached all the required permissions to the API Gateway AWS Identity and Access Management (IAM) role. For instructions, see How do I turn on CloudWatch Logs for troubleshooting my API Gateway REST API or WebSocket API?

Note: HTTP APIs currently support access logging only, and logging setup is different for these APIs. For more information, see Configuring logging for an HTTP API.

Resolution

After you turn on logging, API Gateway automatically creates a CloudWatch log group named API-Gateway-Execution-Logs/{rest-api-id}/{stage-name} . For more information, see CloudWatch log formats for API Gateway.

AWS Lambda authorizers

If you have Lambda authorizers turned on for your API, the logs indicate if the request is authorized and include the authorizer and request IDs.

Example authorized logs:

Starting authorizer: 62mgrc for request: 3323ffe5-6ddf-45c8-896a-b45ec2284cc0
Successfully completed authorizer execution

Example unauthorized logs:

Starting authorizer: 62mgrc for request: fd443056-60d0-425f-874e-e93e5d61351e
Unauthorized request: fd443056-60d0-425f-874e-e93e5d61351e

Usage plans

After the Lambda authorizer logs, API Gateway verifies the usage plan for the API request. If you haven't configured a usage plan, then API requests aren't counted for throttling limits.

Example usage plan logs:

Verifying Usage Plan for request: 3323ffe5-6ddf-45c8-896a-b45ec2284cc0. API Key: API Stage: <api_id>/<stage>
API Key authorized because method 'GET /' does not require API Key. Request will not contribute to throttle or quota limits
Usage Plan check succeeded for API Key and API Stage <api_id>/<stage>

If you have configured APIs with API keys but the X-API-Key header is missing, then the logs return an error similar to the following:

API Key not authorized because method 'GET /' requires API Key and API 
Key is not associated with a Usage Plan for API Stage 
<api_id>/<stage>: API Key was required but not present

If you added the correct API key in the header but the request is throttled, then the logs return an error similar to the following:

API Key **********************************FGQes7 exceeded throttle limit for API Stage <api_id>/<stage>: Key throttle limit exceeded for Usage Plan ID iwuzkt. Limit: 5.00 Burst: 0
Method completed with status: 429

Request log types

Note: All request log types require turning on Log full requests/responses data in the execution logs.

Method request logs

Method request logs includes detailed information received by an API request including the request path, query parameter, request header, and request body.

Endpoint request logs

Endpoint request logs include detailed information received by an API request including the URI, request headers, and request body.

The data included in endpoint requests are sent to your backend integration for further processing.

Endpoint response logs

Endpoint response logs include the data returned by the backend integration including the status code, headers body, and Integration latency.

Method response logs

Method response logs includes the headers and body sent to the client after the transformation.

Important: API Gateway limits log events to 1024 bytes. Log events larger than 1024 bytes, such as request and response bodies, are truncated by API Gateway before submission to CloudWatch logs.


How can I troubleshoot missing CloudWatch logs for API Gateway REST APIs?

Setting up CloudWatch logging for a REST API in API Gateway

Monitoring REST API execution with Amazon CloudWatch metrics

Monitoring WebSocket API execution with CloudWatch metrics

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Troubleshoot API Gateway SSL errors

How can I troubleshoot the API Gateway error “Execution failed due to configuration error: General SSLEngine problem”?

Last updated: 2022-12-01

Amazon API Gateway returned an error for my API request similar to the following:

"Execution failed due to configuration error: General SSLEngine problem"

Resolution

API Gateway API requests perform an SSL handshake on the backend. Successful API Gateway SSL handshakes must include the following requirements:

A supported CA

The CA must be supported by API Gateway for HTTP, HTTP proxy, and private integrations. To check the CA fingerprint, run the following OpenSSL command for your operating system:

Linux

openssl x509 -in cert.pem -fingerprint -sha256 -noout

openssl x509 -in cert.pem -fingerprint -sha1 -noout

Windows

openssl x509 -noout -fingerprint -sha256 -inform pem -in [certificate-file.crt]

openssl x509 -noout -fingerprint -sha1 -inform pem -in [certificate-file.crt]

A valid ACM certificate that isn't expired

To check the expiration date of the certificate, run the following OpenSSL command:

openssl x509 -in certificate.crt -text -noout

In the output, check for the validity timestamp:

Validity
            Not Before: Apr 29 12:49:02 2020 GMT
            Not After : Apr 29 12:49:02 2021 GMT

In this example output, the certificate is valid on April 29, 2020 and expires after April 29, 2021.

A valid CA certificate

Check the CA certificate configuration by running the following OpenSSL command:

openssl s_client -connect example.com:443 -showcerts

Validate that:

  • The subject of the intermediate and certificate matches the issuer of the entity certificate.
  • The subject of the root certificate matches the issuers of the intermediate certificate.
  • The subject and issuer are the same in the root certificate.

A certificate that doesn't exceed 2048 bits

Check the size of the certificate by running the following OpenSSL command:

openssl x509 -in badssl-com.pem -text -noout | grep -E '(Public-Key):'

Note: The certificate size can't exceed 2048 bits.

If your certificate doesn't meet any of these requirements, first update your private CA. Then, reissue a new certificate using AWS Certificate Manager (ACM).


Set up API Gateway private integrations

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Forward host headers for an API Gateway REST API

How can I forward the host header with private integration for an API Gateway REST API?

Last updated: 2022-11-29

I want to use the host header value for my Amazon API Gateway endpoint or custom domain. How can I forward the host header with private integration for an API Gateway REST API?

Short description

Amazon API Gateway overwrites the host value that it receives in the original request to the integration endpoint. Amazon API Gateway assigns the host value depending on the integration request endpoint URL.

To use the host header value of an API Gateway endpoint in the backend, use the custom header. You can use the custom header in the integration request that contains the value of the request host header.

Resolution

Create an API Gateway REST API

1.    Open the API Gateway console.

2.    Choose Create API .

-or-

(If this is your first time using API Gateway) A page that introduces you to the features of the service appears. In REST API , choose Build . When the Create Example API popup appears, choose OK .

3.    For Choose an API type , in the REST API pane, choose Build .

4.    In Create new API , choose New API .

5.    In Settings , do the following:
For API name , enter a name that describes your API's purpose. For example: ForwardHostHeader .
(Optional) For Description , enter a short description of your API's purpose. for example, Forward host header for private integration .
For Endpoint Type , choose either Regional , Edge optimized , or Private .

6.    Choose Create API .

Configure your API's method request and Integration request

1.    Open the API Gateway console.

2.    Follow the instructions to create an API with private integration using the API Gateway console.

3.    In Method Request , add HTTP Request Headers as host.

4.    In Integration Request , expand HTTP Headers , and choose Add header .

5.    Enter a name for the custom header. For example, my_host .

6.    In Mapped from , enter the method request. For example, method.request.header.host , and then choose the check mark icon.

Deploy your API to a new stage

1.    Open the API Gateway console.

2.    Follow the instructions to Deploy a REST API to a stage. For more information, see Setting up a stage using the API Gateway console.

3.    In the Stage Editor pane, copy the Invoke URL to your clipboard. You can use this URL to invoke your API.

REST API invoke URL example:

https://1a2bc3d456.execute-api.us-east-1.amazonaws.com/stage

4.    If you use an Application Load Balancer for your backend, you can test this configuration by adding a rule. Choose "http header" as a condition and specify "my_host" as the same header and value as the API Gateway host value.

5.    Paste the API Gateway URL into a browser window to invoke your API. The "my_host" header configuration in API Gateway forwards the API Gateway host value to the Application Load Balancer. The Application Load Balancer matches the condition set and then returns the response as configured.


Set up request and response data mappings using the API Gateway console

Set up an API using the API Gateway console

Amazon API Gateway important notes

How do I integrate an API Gateway REST API with an Application Load Balancer?

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

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

Last updated: 2022-11-23

I want to integrate an Amazon API Gateway REST API with Amazon Simple Queue Service (Amazon SQS). I also want to troubleshoot integration errors. What steps do I take?

Resolution

Users configure API Gateway REST APIs so that they work with Amazon SQS to create an integrated solution. This article provides steps to integrate API Gateway with Amazon SQS and information to troubleshoot common setup errors.

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 messages from the API to be published 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) .
    For AWS Subdomain , enter Optional .
    For HTTP method , choose POST .
    For Action Type , choose Use path override .
    For Path override (optional) , enter example-account-id/example-sqs-queue-name where you replace example-account-id with your AWS account ID and example-sqs-queue-name with your SQS queue name. For example, 1234567890/MySQSStandardQueue.
    For Execution role , enter the ARN of the IAM role 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 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 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 the SendMessage action isn’t added 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 special characters such as "&" and "%" are passed in the request body payload. The special characters must be encoded 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 needed 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). Permission must be configured 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 needed to perform operations on the KMS keys 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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