Namespace Amazon.CDK.AWS.Logs

Amazon CloudWatch Logs Construct Library

---

This library supplies constructs for working with CloudWatch Logs.

Log Groups/Streams

The basic unit of CloudWatch is a Log Group. Every log group typically has the same kind of data logged to it, in the same format. If there are multiple applications or services logging into the Log Group, each of them creates a new Log Stream.

Every log operation creates a "log event", which can consist of a simple string or a single-line JSON object. JSON objects have the advantage that they afford more filtering abilities (see below).

The only configurable attribute for log streams is the retention period, which configures after how much time the events in the log stream expire and are deleted.

The default retention period if not supplied is 2 years, but it can be set to one of the values in the RetentionDays enum to configure a different retention period (including infinite retention).

// Configure log group for short retention
LogGroup logGroup = new LogGroup(stack, "LogGroup", new LogGroupProps {
    Retention = RetentionDays.ONE_WEEK
});// Configure log group for infinite retention
LogGroup logGroup = new LogGroup(stack, "LogGroup", new LogGroupProps {
    Retention = Infinity
});

LogRetention

The LogRetention construct is a way to control the retention period of log groups that are created outside of the CDK. The construct is usually used on log groups that are auto created by AWS services, such as AWS lambda.

This is implemented using a CloudFormation custom resource which pre-creates the log group if it doesn't exist, and sets the specified log retention period (never expire, by default).

By default, the log group will be created in the same region as the stack. The logGroupRegion property can be used to configure log groups in other regions. This is typically useful when controlling retention for log groups auto-created by global services that publish their log group to a specific region, such as AWS Chatbot creating a log group in us-east-1.

Resource Policy

CloudWatch Resource Policies allow other AWS services or IAM Principals to put log events into the log groups. A resource policy is automatically created when addToResourcePolicy is called on the LogGroup for the first time:

LogGroup logGroup = new LogGroup(this, "LogGroup");
logGroup.AddToResourcePolicy(new PolicyStatement(new PolicyStatementProps {
    Actions = new [] { "logs:CreateLogStream", "logs:PutLogEvents" },
    Principals = new [] { new ServicePrincipal("es.amazonaws.com") },
    Resources = new [] { logGroup.LogGroupArn }
}));

Or more conveniently, write permissions to the log group can be granted as follows which gives same result as in the above example.

LogGroup logGroup = new LogGroup(this, "LogGroup");
logGroup.GrantWrite(new ServicePrincipal("es.amazonaws.com"));

Be aware that any ARNs or tokenized values passed to the resource policy will be converted into AWS Account IDs. This is because CloudWatch Logs Resource Policies do not accept ARNs as principals, but they do accept Account ID strings. Non-ARN principals, like Service principals or Any princpals, are accepted by CloudWatch.

Encrypting Log Groups

By default, log group data is always encrypted in CloudWatch Logs. You have the option to encrypt log group data using a AWS KMS customer master key (CMK) should you not wish to use the default AWS encryption. Keep in mind that if you decide to encrypt a log group, any service or IAM identity that needs to read the encrypted log streams in the future will require the same CMK to decrypt the data.

Here's a simple example of creating an encrypted Log Group using a KMS CMK.

using Amazon.CDK.AWS.KMS;


new LogGroup(this, "LogGroup", new LogGroupProps {
    EncryptionKey = new Key(this, "Key")
});

See the AWS documentation for more detailed information about encrypting CloudWatch Logs.

Subscriptions and Destinations

Log events matching a particular filter can be sent to either a Lambda function or a Kinesis stream.

If the Kinesis stream lives in a different account, a CrossAccountDestination object needs to be added in the destination account which will act as a proxy for the remote Kinesis stream. This object is automatically created for you if you use the CDK Kinesis library.

Create a SubscriptionFilter, initialize it with an appropriate Pattern (see below) and supply the intended destination:

using Amazon.CDK.AWS.Logs.Destinations;
Function fn;
LogGroup logGroup;


new SubscriptionFilter(this, "Subscription", new SubscriptionFilterProps {
    LogGroup = logGroup,
    Destination = new LambdaDestination(fn),
    FilterPattern = FilterPattern.AllTerms("ERROR", "MainThread")
});

Metric Filters

CloudWatch Logs can extract and emit metrics based on a textual log stream. Depending on your needs, this may be a more convenient way of generating metrics for you application than making calls to CloudWatch Metrics yourself.

A MetricFilter either emits a fixed number every time it sees a log event matching a particular pattern (see below), or extracts a number from the log event and uses that as the metric value.

Example:

new MetricFilter(this, "MetricFilter", new MetricFilterProps {
    LogGroup = logGroup,
    MetricNamespace = "MyApp",
    MetricName = "Latency",
    FilterPattern = FilterPattern.Exists("$.latency"),
    MetricValue = "$.latency"
});

Remember that if you want to use a value from the log event as the metric value, you must mention it in your pattern somewhere.

A very simple MetricFilter can be created by using the logGroup.extractMetric() helper function:

LogGroup logGroup;

logGroup.ExtractMetric("$.jsonField", "Namespace", "MetricName");

Will extract the value of jsonField wherever it occurs in JSON-structed log records in the LogGroup, and emit them to CloudWatch Metrics under the name Namespace/MetricName.

Exposing Metric on a Metric Filter

You can expose a metric on a metric filter by calling the MetricFilter.metric() API. This has a default of statistic = 'avg' if the statistic is not set in the props.

LogGroup logGroup;

MetricFilter mf = new MetricFilter(this, "MetricFilter", new MetricFilterProps {
    LogGroup = logGroup,
    MetricNamespace = "MyApp",
    MetricName = "Latency",
    FilterPattern = FilterPattern.Exists("$.latency"),
    MetricValue = "$.latency"
});

//expose a metric from the metric filter
Metric metric = mf.Metric();

//you can use the metric to create a new alarm
//you can use the metric to create a new alarm
new Alarm(this, "alarm from metric filter", new AlarmProps {
    Metric = metric,
    Threshold = 100,
    EvaluationPeriods = 2
});

Patterns

Patterns describe which log events match a subscription or metric filter. There are three types of patterns:

All patterns are constructed by using static functions on the FilterPattern class.

In addition to the patterns above, the following special patterns exist:

Text Patterns

Text patterns match if the literal strings appear in the text form of the log line.

Examples:

// Search for lines that contain both "ERROR" and "MainThread"
IFilterPattern pattern1 = FilterPattern.AllTerms("ERROR", "MainThread");

// Search for lines that either contain both "ERROR" and "MainThread", or
// both "WARN" and "Deadlock".
IFilterPattern pattern2 = FilterPattern.AnyTermGroup(new [] { "ERROR", "MainThread" }, new [] { "WARN", "Deadlock" });

JSON Patterns

JSON patterns apply if the log event is the JSON representation of an object (without any other characters, so it cannot include a prefix such as timestamp or log level). JSON patterns can make comparisons on the values inside the fields.

Fields in the JSON structure are identified by identifier the complete object as $ and then descending into it, such as $.field or $.list[0].field.

Example:

// Search for all events where the component field is equal to
// "HttpServer" and either error is true or the latency is higher
// than 1000.
JsonPattern pattern = FilterPattern.All(FilterPattern.StringValue("$.component", "=", "HttpServer"), FilterPattern.Any(FilterPattern.BooleanValue("$.error", true), FilterPattern.NumberValue("$.latency", ">", 1000)));

Space-delimited table patterns

If the log events are rows of a space-delimited table, this pattern can be used to identify the columns in that structure and add conditions on any of them. The canonical example where you would apply this type of pattern is Apache server logs.

Text that is surrounded by "..." quotes or [...] square brackets will be treated as one column.

After constructing a SpaceDelimitedTextPattern, you can use the following two members to add restrictions:

Multiple restrictions can be added on the same column; they must all apply.

Example:

// Search for all events where the component is "HttpServer" and the
// result code is not equal to 200.
SpaceDelimitedTextPattern pattern = FilterPattern.SpaceDelimited("time", "component", "...", "result_code", "latency").WhereString("component", "=", "HttpServer").WhereNumber("result_code", "!=", 200);

Logs Insights Query Definition

Creates a query definition for CloudWatch Logs Insights.

Example:

new QueryDefinition(this, "QueryDefinition", new QueryDefinitionProps {
    QueryDefinitionName = "MyQuery",
    QueryString = new QueryString(new QueryStringProps {
        Fields = new [] { "@timestamp", "@message" },
        Sort = "@timestamp desc",
        Limit = 20
    })
});

Notes

Be aware that Log Group ARNs will always have the string :* appended to them, to match the behavior of the CloudFormation AWS::Logs::LogGroup resource.

Classes

CfnDestination	A CloudFormation `AWS::Logs::Destination`.
CfnDestinationProps	Properties for defining a `CfnDestination`.
CfnLogGroup	A CloudFormation `AWS::Logs::LogGroup`.
CfnLogGroupProps	Properties for defining a `CfnLogGroup`.
CfnLogStream	A CloudFormation `AWS::Logs::LogStream`.
CfnLogStreamProps	Properties for defining a `CfnLogStream`.
CfnMetricFilter	A CloudFormation `AWS::Logs::MetricFilter`.
CfnMetricFilter.DimensionProperty	Specifies the CloudWatch metric dimensions to publish with this metric.
CfnMetricFilter.MetricTransformationProperty	`MetricTransformation` is a property of the `AWS::Logs::MetricFilter` resource that describes how to transform log streams into a CloudWatch metric.
CfnMetricFilterProps	Properties for defining a `CfnMetricFilter`.
CfnQueryDefinition	A CloudFormation `AWS::Logs::QueryDefinition`.
CfnQueryDefinitionProps	Properties for defining a `CfnQueryDefinition`.
CfnResourcePolicy	A CloudFormation `AWS::Logs::ResourcePolicy`.
CfnResourcePolicyProps	Properties for defining a `CfnResourcePolicy`.
CfnSubscriptionFilter	A CloudFormation `AWS::Logs::SubscriptionFilter`.
CfnSubscriptionFilterProps	Properties for defining a `CfnSubscriptionFilter`.
ColumnRestriction
CrossAccountDestination	A new CloudWatch Logs Destination for use in cross-account scenarios.
CrossAccountDestinationProps	Properties for a CrossAccountDestination.
FilterPattern	A collection of static methods to generate appropriate ILogPatterns.
JsonPattern	Base class for patterns that only match JSON log events.
LogGroup	Define a CloudWatch Log Group.
LogGroupProps	Properties for a LogGroup.
LogRetention	Creates a custom resource to control the retention policy of a CloudWatch Logs log group.
LogRetentionProps	Construction properties for a LogRetention.
LogRetentionRetryOptions	Retry options for all AWS API calls.
LogStream	Define a Log Stream in a Log Group.
LogStreamProps	Properties for a LogStream.
LogSubscriptionDestinationConfig	Properties returned by a Subscription destination.
MetricFilter	A filter that extracts information from CloudWatch Logs and emits to CloudWatch Metrics.
MetricFilterOptions	Properties for a MetricFilter created from a LogGroup.
MetricFilterProps	Properties for a MetricFilter.
QueryDefinition	Define a query definition for CloudWatch Logs Insights.
QueryDefinitionProps	Properties for a QueryDefinition.
QueryString	Define a QueryString.
QueryStringProps	Properties for a QueryString.
ResourcePolicy	Resource Policy for CloudWatch Log Groups.
ResourcePolicyProps	Properties to define Cloudwatch log group resource policy.
RetentionDays	How long, in days, the log contents will be retained.
SpaceDelimitedTextPattern	Space delimited text pattern.
StreamOptions	Properties for a new LogStream created from a LogGroup.
SubscriptionFilter	A new Subscription on a CloudWatch log group.
SubscriptionFilterOptions	Properties for a new SubscriptionFilter created from a LogGroup.
SubscriptionFilterProps	Properties for a SubscriptionFilter.

Interfaces

CfnMetricFilter.IDimensionProperty	Specifies the CloudWatch metric dimensions to publish with this metric.
CfnMetricFilter.IMetricTransformationProperty	`MetricTransformation` is a property of the `AWS::Logs::MetricFilter` resource that describes how to transform log streams into a CloudWatch metric.
ICfnDestinationProps	Properties for defining a `CfnDestination`.
ICfnLogGroupProps	Properties for defining a `CfnLogGroup`.
ICfnLogStreamProps	Properties for defining a `CfnLogStream`.
ICfnMetricFilterProps	Properties for defining a `CfnMetricFilter`.
ICfnQueryDefinitionProps	Properties for defining a `CfnQueryDefinition`.
ICfnResourcePolicyProps	Properties for defining a `CfnResourcePolicy`.
ICfnSubscriptionFilterProps	Properties for defining a `CfnSubscriptionFilter`.
IColumnRestriction
ICrossAccountDestinationProps	Properties for a CrossAccountDestination.
IFilterPattern	Interface for objects that can render themselves to log patterns.
ILogGroup
ILogGroupProps	Properties for a LogGroup.
ILogRetentionProps	Construction properties for a LogRetention.
ILogRetentionRetryOptions	Retry options for all AWS API calls.
ILogStream
ILogStreamProps	Properties for a LogStream.
ILogSubscriptionDestination	Interface for classes that can be the destination of a log Subscription.
ILogSubscriptionDestinationConfig	Properties returned by a Subscription destination.
IMetricFilterOptions	Properties for a MetricFilter created from a LogGroup.
IMetricFilterProps	Properties for a MetricFilter.
IQueryDefinitionProps	Properties for a QueryDefinition.
IQueryStringProps	Properties for a QueryString.
IResourcePolicyProps	Properties to define Cloudwatch log group resource policy.
IStreamOptions	Properties for a new LogStream created from a LogGroup.
ISubscriptionFilterOptions	Properties for a new SubscriptionFilter created from a LogGroup.
ISubscriptionFilterProps	Properties for a SubscriptionFilter.