Setting up application logging - Managed Service for Apache Flink
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Amazon Managed Service for Apache Flink was previously known as Amazon Kinesis Data Analytics for Apache Flink.

Setting up application logging

By adding an Amazon CloudWatch logging option to your Managed Service for Apache Flink application, you can monitor for application events or configuration problems.

This topic describes how to configure your application to write application events to a CloudWatch Logs stream. A CloudWatch logging option is a collection of application settings and permissions that your application uses to configure the way it writes application events to CloudWatch Logs. You can add and configure a CloudWatch logging option using either the Amazon Web Services Management Console or the Amazon Command Line Interface (Amazon CLI).

Note the following about adding a CloudWatch logging option to your application:

  • When you add a CloudWatch logging option using the console, Managed Service for Apache Flink creates the CloudWatch log group and log stream for you and adds the permissions your application needs to write to the log stream.

  • When you add a CloudWatch logging option using the API, you must also create the application's log group and log stream, and add the permissions your application needs to write to the log stream.

Setting up CloudWatch logging using the console

When you enable CloudWatch logging for your application in the console, a CloudWatch log group and log stream is created for you. Also, your application's permissions policy is updated with permissions to write to the stream.

Managed Service for Apache Flink creates a log group named using the following convention, where ApplicationName is your application's name.

/AWS/KinesisAnalytics/ApplicationName

Managed Service for Apache Flink creates a log stream in the new log group with the following name.

kinesis-analytics-log-stream

You set the application monitoring metrics level and monitoring log level using the Monitoring log level section of the Configure application page. For information about application log levels, see Application monitoring levels.

Setting up CloudWatch logging using the CLI

To add a CloudWatch logging option using the Amazon CLI, do the following:

  • Create a CloudWatch log group and log stream.

  • Add a logging option when you create an application by using the CreateApplication action, or add a logging option to an existing application using the AddApplicationCloudWatchLoggingOption action.

  • Add permissions to your application's policy to write to the logs.

Creating a CloudWatch log group and log stream

You create a CloudWatch log group and stream using either the CloudWatch Logs console or the API. For information about creating a CloudWatch log group and log stream, see Working with Log Groups and Log Streams.

Working with application CloudWatch logging options

Use the following API actions to add a CloudWatch log option to a new or existing application or change a log option for an existing application. For information about how to use a JSON file for input for an API action, see Managed Service for Apache Flink API example code.

Adding a CloudWatch log option when creating an application

The following example demonstrates how to use the CreateApplication action to add a CloudWatch log option when you create an application. In the example, replace Amazon Resource Name (ARN) of the CloudWatch Log stream to add to the new application with your own information. For more information about the action, see CreateApplication.

{ "ApplicationName": "test", "ApplicationDescription": "test-application-description", "RuntimeEnvironment": "FLINK-1_15", "ServiceExecutionRole": "arn:aws:iam::123456789123:role/myrole", "ApplicationConfiguration": { "ApplicationCodeConfiguration": { "CodeContent": { "S3ContentLocation":{ "BucketARN": "arn:aws:s3:::mybucket", "FileKey": "myflink.jar" } }, "CodeContentType": "ZIPFILE" } }, "CloudWatchLoggingOptions": [{ "LogStreamARN": "<Amazon Resource Name (ARN) of the CloudWatch log stream to add to the new application>" }] }

Adding a CloudWatch log option to an existing application

The following example demonstrates how to use the AddApplicationCloudWatchLoggingOption action to add a CloudWatch log option to an existing application. In the example, replace each user input placeholder with your own information. For more information about the action, see AddApplicationCloudWatchLoggingOption.

{ "ApplicationName": "<Name of the application to add the log option to>", "CloudWatchLoggingOption": { "LogStreamARN": "<ARN of the log stream to add to the application>" }, "CurrentApplicationVersionId": <Version of the application to add the log to> }

Updating an existing CloudWatch log option

The following example demonstrates how to use the UpdateApplication action to modify an existing CloudWatch log option. In the example, replace each user input placeholder with your own information. For more information about the action, see UpdateApplication.

{ "ApplicationName": "<Name of the application to update the log option for>", "CloudWatchLoggingOptionUpdates": [ { "CloudWatchLoggingOptionId": "<ID of the logging option to modify>", "LogStreamARNUpdate": "<ARN of the new log stream to use>" } ], "CurrentApplicationVersionId": <ID of the application version to modify> }

Deleting a CloudWatch log option from an application

The following example demonstrates how to use the DeleteApplicationCloudWatchLoggingOption action to delete an existing CloudWatch log option. In the example, replace each user input placeholder with your own information. For more information about the action, see DeleteApplicationCloudWatchLoggingOption.

{ "ApplicationName": "<Name of application to delete log option from>", "CloudWatchLoggingOptionId": "<ID of the application log option to delete>", "CurrentApplicationVersionId": <Version of the application to delete the log option from> }

Setting the application logging level

To set the level of application logging, use the MonitoringConfiguration parameter of the CreateApplication action or the MonitoringConfigurationUpdate parameter of the UpdateApplication action.

For information about application log levels, see Application monitoring levels.

Set the application logging level when creating an application

The following example request for the CreateApplication action sets the application log level to INFO.

{ "ApplicationName": "MyApplication", "ApplicationDescription": "My Application Description", "ApplicationConfiguration": { "ApplicationCodeConfiguration":{ "CodeContent":{ "S3ContentLocation":{ "BucketARN":"arn:aws:s3:::mybucket", "FileKey":"myflink.jar", "ObjectVersion":"AbCdEfGhIjKlMnOpQrStUvWxYz12345" } }, "CodeContentType":"ZIPFILE" }, "FlinkApplicationConfiguration": "MonitoringConfiguration": { "ConfigurationType": "CUSTOM", "LogLevel": "INFO" } }, "RuntimeEnvironment": "FLINK-1_15", "ServiceExecutionRole": "arn:aws:iam::123456789123:role/myrole" }
Update the application logging level

The following example request for the UpdateApplication action sets the application log level to INFO.

{ "ApplicationConfigurationUpdate": { "FlinkApplicationConfigurationUpdate": { "MonitoringConfigurationUpdate": { "ConfigurationTypeUpdate": "CUSTOM", "LogLevelUpdate": "INFO" } } } }

Adding permissions to write to the CloudWatch log stream

Managed Service for Apache Flink needs permissions to write misconfiguration errors to CloudWatch. You can add these permissions to the Amazon Identity and Access Management (IAM) role that Managed Service for Apache Flink assumes.

For more information about using an IAM role for Managed Service for Apache Flink, see Identity and Access Management for Amazon Managed Service for Apache Flink.

Trust policy

To grant Managed Service for Apache Flink permissions to assume an IAM role, you can attach the following trust policy to the service execution role.

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Principal": { "Service": "kinesisanlaytics.amazonaws.com" }, "Action": "sts:AssumeRole" } ] }

Permissions policy

To grant permissions to an application to write log events to CloudWatch from a Managed Service for Apache Flink resource, you can use the following IAM permissions policy. Provide the correct Amazon Resource Names (ARNs) for your log group and stream.

{ "Version": "2012-10-17", "Statement": [ { "Sid": "Stmt0123456789000", "Effect": "Allow", "Action": [ "logs:PutLogEvents", "logs:DescribeLogGroups", "logs:DescribeLogStreams" ], "Resource": [ "arn:aws:logs:us-east-1:123456789012:log-group:my-log-group:log-stream:my-log-stream*", "arn:aws:logs:us-east-1:123456789012:log-group:my-log-group:*", "arn:aws:logs:us-east-1:123456789012:log-group:*", ] } ] }

Application monitoring levels

You control the generation of application log messages using the application's Monitoring Metrics Level and Monitoring Log Level.

The application's monitoring metrics level controls the granularity of log messages. Monitoring metrics levels are defined as follows:

The application's monitoring log level controls the verbosity of the application's log. Monitoring log levels are defined as follows:

  • Error: Potential catastrophic events of the application.

  • Warn: Potentially harmful situations of the application.

  • Info: Informational and transient failure events of the application. We recommend that you use this logging level.

  • Debug: Fine-grained informational events that are most useful to debug an application. Note: Only use this level for temporary debugging purposes.

Logging best practices

We recommend that your application use the Info logging level. We recommend this level to ensure that you see Apache Flink errors, which are logged at the Info level rather than the Error level.

We recommend that you use the Debug level only temporarily while investigating application issues. Switch back to the Info level when the issue is resolved. Using the Debug logging level will significantly affect your application's performance.

Excessive logging can also significantly impact application performance. We recommend that you do not write a log entry for every record processed, for example. Excessive logging can cause severe bottlenecks in data processing and can lead to back pressure in reading data from the sources.

Logging troubleshooting

If application logs are not being written to the log stream, verify the following:

Next step

After you have enabled CloudWatch logging in your application, you can use CloudWatch Logs Insights to analyze your application logs. For more information, see Analyzing logs with CloudWatch Logs Insights.