Working with log groups and log streams - Amazon CloudWatch Logs
Create a log groupSend logs to a log groupView log dataChange log data retentionTag log groups

Working with log groups and log streams

A log stream is a sequence of log events that share the same source. Each separate source of logs in CloudWatch Logs makes up a separate log stream.

A log group is a group of log streams that share the same retention, monitoring, and access control settings. You can define log groups and specify which streams to put into each group. There is no limit on the number of log streams that can belong to one log group.

Use the procedures in this section to work with log groups and log streams.

Create a log group in CloudWatch Logs

When you install the CloudWatch Logs agent on an Amazon EC2 instance using the steps in previous sections of the Amazon CloudWatch Logs User Guide, the log group is created as part of that process. You can also create a log group directly in the CloudWatch console.

To create a log group

  1. Open the CloudWatch console at https://console.aws.amazon.com/cloudwatch/.

  2. In the navigation pane, choose Log groups.

  3. Choose Actions, and then choose Create log group.

  4. Enter a name for the log group, and then choose Create log group.

Send logs to a log group

CloudWatch Logs automatically receives log events from several AWS services. You can also send other log events to CloudWatch Logs using one of the following methods:

View log data sent to CloudWatch Logs

You can view and scroll through log data on a stream-by-stream basis as sent to CloudWatch Logs by the CloudWatch Logs agent. You can specify the time range for the log data to view.

To view log data

  1. Open the CloudWatch console at https://console.aws.amazon.com/cloudwatch/.

  2. In the navigation pane, choose Log groups.

  3. For Log Groups, choose the log group to view the streams.

  4. In the list of log groups, choose the name of the log group that you want to view.

  5. In the list of log streams, choose the name of the log stream that you want to view.

  6. To change how the log data is displayed, do one of the following:

    • To expand a single log event, choose the arrow next to that log event.

    • To expand all log events and view them as plain text, above the list of log events, choose Text.

    • To filter the log events, enter the desired search filter in the search field. For more information, see Creating metrics from log events using filters.

    • To view log data for a specified date and time range, next to the search filter, choose the arrow next to the date and time. To specify a date and time range, choose Absolute. To choose a predefined number of minutes, hours, days, or weeks, choose Relative. You can also switch between UTC and local time zone.

Change log data retention in CloudWatch Logs

By default, log data is stored in CloudWatch Logs indefinitely. However, you can configure how long to store log data in a log group. Any data older than the current retention setting is deleted automatically. You can change the log retention for each log group at any time.

To change the logs retention setting

  1. Open the CloudWatch console at https://console.aws.amazon.com/cloudwatch/.

  2. In the navigation pane, choose Log groups.

  3. Find the log group to update.

  4. In the Expire Events After column for that log group, choose the current retention setting, such as Never Expire.

  5. In Edit Retention, for Retention, choose a log retention value, and then choose Ok.

Tag log groups in Amazon CloudWatch Logs

You can assign your own metadata to the log groups you create in Amazon CloudWatch Logs in the form of tags. A tag is a key-value pair that you define for a log group. Using tags is a simple yet powerful way to manage AWS resources and organize data, including billing data.

Note

CloudWatch Logs doesn’t support IAM policies that prevent users from assigning specified tags to log groups using the aws:Resource/key-name or aws:TagKeys condition keys. For more information about using tags to control access, see Controlling access to Amazon Web Services resources using tags.

Tag basics

You use the AWS CLI or CloudWatch Logs API to complete the following tasks:

  • Add tags to a log group when you create it.

  • Add tags to an existing log group.

  • List the tags for a log group.

  • Remove tags from a log group.

You can use tags to categorize your log groups. For example, you can categorize them by purpose, owner, or environment. Because you define the key and value for each tag, you can create a custom set of categories to meet your specific needs. For example, you might define a set of tags that helps you track log groups by owner and associated application. Here are several examples of tags:

  • Project: Project name

  • Owner: Name

  • Purpose: Load testing

  • Application: Application name

  • Environment: Production

Tracking costs using tagging

You can use tags to categorize and track your AWS costs. When you apply tags to your AWS resources, including log groups, your AWS cost allocation report includes usage and costs aggregated by tags. You can apply tags that represent business categories (such as cost centers, application names, or owners) to organize your costs across multiple services. For more information, see Use Cost Allocation Tags for Custom Billing Reports in the AWS Billing and Cost Management User Guide.

Tag restrictions

The following restrictions apply to tags.

Basic restrictions

  • The maximum number of tags per log group is 50.

  • Tag keys and values are case sensitive.

  • You can't change or edit tags for a deleted log group.

Tag key restrictions

  • Each tag key must be unique. If you add a tag with a key that's already in use, your new tag overwrites the existing key-value pair.

  • You can't start a tag key with aws: because this prefix is reserved for use by AWS. AWS creates tags that begin with this prefix on your behalf, but you can't edit or delete them.

  • Tag keys must be between 1 and 128 Unicode characters in length.

  • Tag keys must consist of the following characters: Unicode letters, digits, white space, and the following special characters: _ . / = + - @.

Tag value restrictions

  • Tag values must be between 0 and 255 Unicode characters in length.

  • Tag values can be blank. Otherwise, they must consist of the following characters: Unicode letters, digits, white space, and any of the following special characters: _ . / = + - @.

Tagging log groups using the AWS CLI

You can add, list, and remove tags using the AWS CLI. For examples, see the following documentation:

create-log-group

Creates a log group. You can optionally add tags when you create the log group.

tag-log-group

Adds or updates tags for the specified log group.

list-tags-log-group

Lists the tags for the specified log group.

untag-log-group

Removes tags from the specified log group.

Tagging log groups using the CloudWatch Logs API

You can add, list, and remove tags using the CloudWatch Logs API. For examples, see the following documentation:

CreateLogGroup

Creates a log group. You can optionally add tags when you create the log group.

TagLogGroup

Adds or updates tags for the specified log group.

ListTagsLogGroup

Lists the tags for the specified log group.

UntagLogGroup

Removes tags from the specified log group.