This document explains how Cloud Logging processes log entries, and describes the key components of Logging routing and storage. Routing refers to the process that Cloud Logging uses to determine what to do with a newly-arrived log entry. You can route log entries to destinations like Logging buckets, which store the log entry, or to Pub/Sub. To export your logs into third-party destinations, route your logs to a Pub/Sub topic, and then authorize the third-party destination to subscribe to the Pub/Sub topic.
At a high level, this is how Cloud Logging routes and stores log entries:
Route logs with the Log Router
The following sections explain how Logging routes logs with the Log Router by using sinks.
Log Router
A log entry is sent to the
Google Cloud resource
specified in its logName field
during its
entries.write call.
Cloud Logging receives log entries with the Cloud Logging API where they pass through the Log Router. The sinks in the Log Router check each log entry against their inclusion filter and exclusion filters, and then determine which destinations, including Cloud Logging buckets, that the log entry should be sent to. You can use combinations of sinks to route a log entry to multiple destinations.
The Log Router stores the log entry temporarily. This behavior buffers against temporary disruptions and outages that might occur when a sink routes a log entry to a destination. The buffering doesn't protect against sink configuration errors. If your sink is configured incorrectly, then it doesn't route log entries, an error log is generated, and an email notifying you of a sink configuration error is sent. When log entries can't be routed, they are discarded.
The Log Router's temporary storage is distinct from the longer term storage provided by Logging buckets.
Incoming log entries with timestamps that are more than the logs retention period in the past or that are more than 24 hours in the future are discarded.
Sinks
Sinks control how Cloud Logging routes logs. Using sinks, you can route some or all of your logs to supported destinations. Some of the reasons that you might want to control how your logs are routed include the following:
- To store logs that are unlikely to be read but that must be retained for compliance purposes.
- To organize your logs in buckets in a format that is useful to you.
- To use big-data analysis tools on your logs.
- To stream your logs to other applications, other repositories, or third parties. For example, if you want to export your logs from Google Cloud so that you can view them on a third-party platform, then configure a sink to route your log entries to Pub/Sub.
Sinks belong to a given Google Cloud resource: Google Cloud projects, billing accounts, folders, and organizations. When the resource receives a log entry, it routes the log entry according to the sinks contained by that resource and, if enabled, any ancestral sinks belonging under the resource hierarchy. The log entry is sent to the destination associated with each matching sink.
Cloud Logging provides two predefined sinks for each Google Cloud project,
billing account, folder, and organization: _Required and _Default. All logs
that are generated in a resource are automatically processed through these two
sinks and then are stored either in the correspondingly named
_Required or
_Default buckets.
Sinks act independently of each other. Regardless of how the predefined sinks process your log entries, you can create your own sinks to route some or all of your logs to various supported destinations or to exclude them from being stored by Cloud Logging.
Which log entries are routed by a sink is controlled by configuring the sink's inclusion filter and exclusion filters. Depending on the sink's configuration, every log entry received by Cloud Logging falls into one or more of these categories:
Stored in Cloud Logging and not routed elsewhere.
Stored in Cloud Logging and routed to a supported destination.
Not stored in Cloud Logging but routed to a supported destination.
Neither stored in Cloud Logging nor routed elsewhere.
You usually create sinks at the Google Cloud project level, but if you want to combine and route logs from the resources contained by a Google Cloud organization or folder, you can create aggregated sinks.
Sinks only route log entries that arrive after the sink is created because routing happens as logs pass through the Logging API. If you need to route log entries retroactively, see Copy logs.Inclusion filters
When a sink doesn't specify any filters, all log entries match and are routed to the sink's destination. You can configure the sink to select specific log entries by setting an inclusion filter. You can also set one or more exclusion filters to exclude log entries from being routed.
When you configure a sink, you specify its filters by using the Logging query language.
A log entry is routed by a sink based on these rules:
If the log entry doesn't match the inclusion filter, then it isn't routed. When a sink doesn't specify an inclusion filter, then every log entry matches that filter.
If the log entry matches the inclusion filter and at least one exclusion filter, then it isn't routed.
If the log entry matches the inclusion filter and doesn't match any exclusion filter, then it is routed to the sink's destination.
Exclusion filters
When you create a sink, you can set multiple exclusion filters. Exclusion filters let you exclude log entries that match the inclusion filter from being routed to the sink's destination or from being stored in a log bucket. You define exclusion filters by using the Logging query language.
Excluded log entries consume
entries.write API quota because they are
excluded after they are received by the Logging API.
You can't reduce the number of
entries.write API calls by
excluding log entries.
Excluded log entries aren't available in the Logs Explorer.
Log entries that aren't routed to at least one log bucket, either explicitly with exclusion filters or because they don't match any sinks with a Logging storage destination, are also excluded from Error Reporting. Therefore, these log entries aren't available to help troubleshoot failures. User-defined log-based metrics are computed from log entries in both included and excluded log entries. For more information, see Monitor your logs.Supported destinations
You can use the Log Router to route certain log entries to supported destinations in any Google Cloud project. When the destination of a log sink is a project, the log sinks in that project reroute the log entries. Log entries aren't rerouted for any other destination. For example, if you route log entries from one project to a log bucket in another project, then those log entries aren't rerouted by the log sinks in the project that stores the log bucket:
Logging supports the following sink destinations:
Cloud Logging bucket: Provides storage in Cloud Logging. A log bucket can store log entries that are received by multiple Google Cloud projects. The log bucket can be in the same project in which log entries originate, or in a different project. For information about viewing log entries stored in log buckets, see Query and view logs overview and View logs routed to Cloud Logging buckets.
You can combine your Cloud Logging data with other data by upgrading a log bucket to use Log Analytics, and then creating a linked dataset, which is a read-only dataset that can be queried by the BigQuery Studio and Looker Studio pages.
BigQuery dataset: Provides storage of log entries in a writeable BigQuery dataset. The BigQuery dataset can be in the same project in which log entries originate, or in a different project. You can use big data analysis capabilities on the stored log entries. For information about viewing log entries routed to BigQuery, see View logs routed to BigQuery.
- Cloud Storage bucket: Provides storage of log entries in Cloud Storage. The Cloud Storage bucket can be in the same project in which log entries originate, or in a different project. Log entries are stored as JSON files. For information about viewing log entries routed to Cloud Storage, see View logs routed to Cloud Storage.
- Pub/Sub topic: Provides support for third-party integrations like Splunk or Datadog. Log entries are formatted into JSON and then routed to a Pub/Sub topic. The topic can be in the same project in which log entries originate, or in a different project. For information about viewing log entries routed to Pub/Sub, see View logs routed to Pub/Sub.
- Google Cloud project: Route log entries to another Google Cloud project. In this configuration, the sinks in the destination project processes the log entries.
For information about how to create a sink and how to configure the options you might see when using the Google Cloud console or the API, see Route logs to supported destinations.
How routing log entries affects log-based metrics
Log-based metrics are Cloud Monitoring metrics that are derived from the content of log entries. For example, if Cloud Logging receives a log entry for a Google Cloud project that matches the filters of one of the Google Cloud project's metrics, then that log entry is counted in the metric data.
Log-based metrics interact with routing differently, depending on whether the log-based metrics are defined by the system or by you. The following sections describe these differences.
Log-based metrics and exclusion filters
Sink exclusion filters apply to system-defined log-based metrics, which count only logs that are stored in log buckets.
Sink exclusion filters don't apply to user-defined log-based metrics. Even if you exclude logs from being stored in any Logging buckets, you could see those logs counted in these metrics.
Scope of log-based metrics
System-defined log-based metrics apply at the Google Cloud project level. These metrics are calculated by the Log Router and only apply to log entries that pass through the sinks of a Google Cloud project.
User-defined log-based metrics can apply at either the Google Cloud project level or at the level of a specific log bucket:
- Project-level metrics are calculated like system-defined log-based metrics; these user-defined log-based metrics apply to log entries that pass through the sinks of a Google Cloud project.
Bucket-scoped metrics apply to the log entries in the log bucket in which they're received, regardless of the Google Cloud project in which the log entries originated.
With bucket-scoped log-based metrics, you can create log-based metrics that can evaluate log entries in the following cases:
- Log entries that are routed from one project to a bucket in another project.
- Log entries that are routed into a bucket through an aggregated sink.
For more information, see Log-based metrics overview.
Best practices
For best practices about using routing for data governance or for common use cases, see the following documents:
Pricing
Cloud Logging doesn't charge to route logs to a
supported destination; however, the destination might apply charges.
With the exception of the _Required log bucket,
Cloud Logging charges to stream logs into log buckets and
for storage longer than the default retention period of the log bucket.
Cloud Logging doesn't charge for copying logs, for creating log scopes or analytics views, or for queries issued through the Logs Explorer or Log Analytics pages.
For more information, see the following documents:
- Cloud Logging pricing summary
Destination costs:
- VPC flow log generation charges apply when you send and then exclude your Virtual Private Cloud flow logs from Cloud Logging.
What's next
To help you route and store Cloud Logging data, see the following documents:
To create sinks to route log entries to supported destinations, see Route logs to supported destinations.
To learn how to create aggregated sinks that can route log entries from the resources in folders or organizations, see Collate and route organization- and folder-level logs to supported destinations.
To learn about the format of routed log entries and how the logs are organized in destinations, see the following documents: