Setting up CloudWatch logging for a REST API in API Gateway - Amazon API Gateway
CloudWatch log formats for API GatewayPermissions for CloudWatch loggingSet up CloudWatch API logging using the API Gateway consoleSet up CloudWatch API logging using AWS CloudFormation

Setting up CloudWatch logging for a REST API in API Gateway

To help debug issues related to request execution or client access to your API, you can enable Amazon CloudWatch Logs to log API calls. For more information about CloudWatch, see Monitoring REST API execution with Amazon CloudWatch metrics.

CloudWatch log formats for API Gateway

There are two types of API logging in CloudWatch: execution logging and access logging. In execution logging, API Gateway manages the CloudWatch Logs. The process includes creating log groups and log streams, and reporting to the log streams any caller's requests and responses.

The logged data includes errors or execution traces (such as request or response parameter values or payloads), data used by Lambda authorizers (formerly known as custom authorizers), whether API keys are required, whether usage plans are enabled, and so on.

When you deploy an API, API Gateway creates a log group and log streams under the log group. The log group is named following the API-Gateway-Execution-Logs_{rest-api-id}/{stage_name} format. Within each log group, the logs are further divided into log streams, which are ordered by Last Event Time as logged data is reported.

In access logging, you, as an API developer, want to log who has accessed your API and how the caller accessed the API. You can create your own log group or choose an existing log group that could be managed by API Gateway. To specify the access details, you select $context variables (expressed in a format of your choosing) and choose a log group as the destination. The access log format must include at least $context.requestId or $context.extendedRequestId. As a best practice, include $context.requestId and $context.extendedRequestId in your log format. $context.requestId logs the value in the x-amzn-RequestId header. Clients can override the value in the x-amzn-RequestId header with a value in the format of a universally unique identifier (UUID). API Gateway returns this request ID in the x-amzn-RequestId response header. API Gateway replaces overridden request IDs that aren't in the format of a UUID with UUID_REPLACED_INVALID_REQUEST_ID in your access logs. $context.extendedRequestId is a unique ID that API Gateway generates. API Gateway returns this request ID in the x-amz-apigw-id response header. An API caller can't provide or override this request ID. For more information, see $context Variables for data models, authorizers, mapping templates, and CloudWatch access logging.

Note

Only $context variables are supported (not $input, and so on).

Choose a log format that is also adopted by your analytic backend, such as Common Log Format (CLF), JSON, XML, or CSV. You can then feed the access logs to it directly to have your metrics computed and rendered. To define the log format, set the log group ARN on the accessLogSettings/destinationArn property on the stage. You can obtain a log group ARN in the CloudWatch console, provided that the ARN column is selected for display. To define the access log format, set a chosen format on the accessLogSetting/format property on the stage.

Examples of some commonly used access log formats are shown in the API Gateway console and are listed as follows.

  • CLF (Common Log Format):

    $context.identity.sourceIp $context.identity.caller  \
$context.identity.user [$context.requestTime] \
"$context.httpMethod $context.resourcePath $context.protocol" \
$context.status $context.responseLength $context.requestId $context.extendedRequestId

    The continuation characters (\) are meant as a visual aid. The log format must be a single line. You can add a newline character (\n) at the end of the log format to include a newline at the end of each log entry.

  • JSON: 

    { "requestId":"$context.requestId", \
  "extendedRequestId":"$context.extendedRequestId", \
  "ip": "$context.identity.sourceIp", \
  "caller":"$context.identity.caller", \
  "user":"$context.identity.user", \
  "requestTime":"$context.requestTime", \
  "httpMethod":"$context.httpMethod", \
  "resourcePath":"$context.resourcePath", \
  "status":"$context.status", \
  "protocol":"$context.protocol", \
  "responseLength":"$context.responseLength" \
}

    The continuation characters (\) are meant as a visual aid. The log format must be a single line. You can add a newline character (\n) at the end of the log format to include a newline at the end of each log entry.

  • XML: 

    <request id="$context.requestId"> \
    <extendedRequestId>$context.extendedRequestId</extendedRequestId>
    <ip>$context.identity.sourceIp</ip> \
    <caller>$context.identity.caller</caller> \
    <user>$context.identity.user</user> \
    <requestTime>$context.requestTime</requestTime> \
    <httpMethod>$context.httpMethod</httpMethod> \
    <resourcePath>$context.resourcePath</resourcePath> \
    <status>$context.status</status> \
    <protocol>$context.protocol</protocol> \
    <responseLength>$context.responseLength</responseLength> \
</request>

    The continuation characters (\) are meant as a visual aid. The log format must be a single line. You can add a newline character (\n) at the end of the log format to include a newline at the end of each log entry.

  • CSV (comma-separated values):

    $context.identity.sourceIp,$context.identity.caller,\
$context.identity.user,$context.requestTime,$context.httpMethod,\
$context.resourcePath,$context.protocol,$context.status,\
$context.responseLength,$context.requestId,$context.extendedRequestId

    The continuation characters (\) are meant as a visual aid. The log format must be a single line. You can add a newline character (\n) at the end of the log format to include a newline at the end of each log entry.

Permissions for CloudWatch logging

To enable CloudWatch Logs, you must grant API Gateway permission to read and write logs to CloudWatch for your account. The AmazonAPIGatewayPushToCloudWatchLogs managed policy (with an ARN of arn:aws:iam::aws:policy/service-role/AmazonAPIGatewayPushToCloudWatchLogs) has all the required permissions:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "logs:CreateLogGroup",
                "logs:CreateLogStream",
                "logs:DescribeLogGroups",
                "logs:DescribeLogStreams",
                "logs:PutLogEvents",
                "logs:GetLogEvents",
                "logs:FilterLogEvents"
            ],
            "Resource": "*"
        }
    ]
}
Note

API Gateway calls AWS Security Token Service in order to assume the IAM role, so make sure that AWS STS is enabled for the Region. For more information, see Managing AWS STS in an AWS Region.

To grant these permissions to your account, create an IAM role with apigateway.amazonaws.com as its trusted entity, attach the preceding policy to the IAM role, and set the IAM role ARN on the cloudWatchRoleArn property on your Account. You must set the cloudWatchRoleArn property separately for each AWS Region in which you want to enable CloudWatch Logs.

If you receive an error when setting the IAM role ARN, check your AWS Security Token Service account settings to make sure that AWS STS is enabled in the Region that you're using. For more information about enabling AWS STS, see Managing AWS STS in an AWS Region in the IAM User Guide.

Set up CloudWatch API logging using the API Gateway console

To set up CloudWatch API logging, you must have deployed the API to a stage. You must also have configured an appropriate CloudWatch Logs role ARN for your account.

  1. Sign in to the API Gateway console at https://console.aws.amazon.com/apigateway.

  2. Choose a REST API.

  3. Choose Settings from the primary navigation panel and enter an ARN of an IAM role with appropriate permissions in CloudWatch log role ARN. You need to do this once.

  4. Do one of the following:

    1. Choose an existing API and then choose a stage.

    2. Create an API and deploy it to a stage.

  5. Choose Logs/Tracing in the Stage Editor.

  6. To enable execution logging:

    1. Choose a logging level from the CloudWatch Logs dropdown menu.

      Warning

      Full Request and Response Logs can be useful to troubleshoot APIs, but can result in logging sensitive data. We recommend that you don't use Full Request and Response Logs for production APIs.

    2. If desired, choose Enable Detailed CloudWatch Metrics.

    For more information about CloudWatch metrics, see Monitoring REST API execution with Amazon CloudWatch metrics.

  7. To enable access logging:

    1. Choose Enable Access Logging under Custom Access Logging.

    2. Enter the ARN of a log group in Access Log Destination ARN. The ARN format is arn:aws:logs:{region}:{account-id}:log-group:log-group-name.

    3. Enter a log format in Log Format. You can choose CLF, JSON, XML, or CSV to use one of the provided examples as a guide.

  8. Choose Save Changes.

Note

You can enable execution logging and access logging independent of each other.

API Gateway is now ready to log requests to your API. You don't need to redeploy the API when you update the stage settings, logs, or stage variables.

Set up CloudWatch API logging using AWS CloudFormation

Use the following example AWS CloudFormation template to create an Amazon CloudWatch Logs log group and configure execution and access logging for a stage.

  TestStage:
    Type: AWS::ApiGateway::Stage
    Properties:
      StageName: test
      RestApiId: !Ref MyAPI
      DeploymentId: !Ref Deployment
      Description: "test stage description"
      MethodSettings:
        - ResourcePath: "/*"
          HttpMethod: "*"
          LoggingLevel: INFO
      AccessLogSetting:
        DestinationArn: !GetAtt MyLogGroup.Arn
        Format: $context.extendedRequestId $context.identity.sourceIp $context.identity.caller $context.identity.user [$context.requestTime] "$context.httpMethod $context.resourcePath $context.protocol" $context.status $context.responseLength $context.requestId
  MyLogGroup:
    Type: AWS::Logs::LogGroup
    Properties:
      LogGroupName: !Join
        - '-'
        - - !Ref MyAPI
          - access-logs