ETW logging driver

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The ETW logging driver forwards container logs as ETW events. ETW stands for Event Tracing in Windows, and is the common framework for tracing applications in Windows. Each ETW event contains a message with both the log and its context information. A client can then create an ETW listener to listen to these events.

The ETW provider that this logging driver registers with Windows, has the GUID identifier of: {a3693192-9ed6-46d2-a981-f8226c8363bd}. A client creates an ETW listener and registers to listen to events from the logging driver’s provider. It does not matter the order in which the provider and listener are created. A client can create their ETW listener and start listening for events from the provider, before the provider has been registered with the system.

Usage

Here is an example of how to listen to these events using the logman utility program included in most installations of Windows:

  1. logman start -ets DockerContainerLogs -p {a3693192-9ed6-46d2-a981-f8226c8363bd} 0 0 -o trace.etl
  2. Run your container(s) with the etwlogs driver, by adding --log-driver=etwlogs to the Docker run command, and generate log messages.
  3. logman stop -ets DockerContainerLogs
  4. This generates an etl file that contains the events. One way to convert this file into human-readable form is to run: tracerpt -y trace.etl.

Each ETW event contains a structured message string in this format:

container_name: %s, image_name: %s, container_id: %s, image_id: %s, source: [stdout | stderr], log: %s

Details on each item in the message can be found below:

Field Description
container_name The container name at the time it was started.
image_name The name of the container’s image.
container_id The full 64-character container ID.
image_id The full ID of the container’s image.
source stdout or stderr.
log The container log message.

Here is an example event message:

container_name: backstabbing_spence,
image_name: windowsservercore,
container_id: f14bb55aa862d7596b03a33251c1be7dbbec8056bbdead1da8ec5ecebbe29731,
image_id: sha256:2f9e19bd998d3565b4f345ac9aaf6e3fc555406239a4fb1b1ba879673713824b,
source: stdout,
log: Hello world!

A client can parse this message string to get both the log message, as well as its context information. The timestamp is also available within the ETW event.

Note: This ETW provider emits only a message string, and not a specially structured ETW event. Therefore, it is not required to register a manifest file with the system to read and interpret its ETW events.

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