Non-Blocking Log Delivery, Environment Variables, and Supported Logging Drivers

- non-blocking delivery that stores log messages in an intermediate per-container buffer for consumption by driver The `non-blocking` message delivery mode prevents applications from blocking due to logging back pressure. Applications are likely to fail in unexpected ways when STDERR or STDOUT streams block. > [!WARNING] > > When the buffer is full, new messages will not be enqueued. Dropping messages is often preferred to blocking the > log-writing process of an application. The `mode` log option controls whether to use the `blocking` (default) or `non-blocking` message delivery. The `max-buffer-size` controls the size of the buffer used for intermediate message storage when `mode` is set to `non-blocking`. The default is `1m` meaning 1 MB (1 million bytes). See [function `FromHumanSize()` in the `go-units` package](https://pkg.go.dev/github.com/docker/go-units#FromHumanSize) for the allowed format strings, some examples are `1KiB` for 1024 bytes, `2g` for 2 billion bytes. The following example starts an Alpine container with log output in non-blocking mode and a 4 megabyte buffer: ```console $ docker run -it --log-opt mode=non-blocking --log-opt max-buffer-size=4m alpine ping 127.0.0.1 ``` ### Use environment variables or labels with logging drivers Some logging drivers add the value of a container's `--env|-e` or `--label` flags to the container's logs. This example starts a container using the Docker daemon's default logging driver (in the following example, `json-file`) but sets the environment variable `os=ubuntu`. ```console $ docker run -dit --label production_status=testing -e os=ubuntu alpine sh ``` If the logging driver supports it, this adds additional fields to the logging output. The following output is generated by the `json-file` logging driver: ```json "attrs":{"production_status":"testing","os":"ubuntu"} ``` ## Supported logging drivers The following logging drivers are supported. See the link to each driver's documentation for its configurable options, if applicable. If you are using [logging driver plugins](plugins.md), you may see more options. | Driver | Description |

Docker's non-blocking log delivery mode prevents application blocking by buffering log messages, controlled by `mode=non-blocking` and `max-buffer-size` (default 1MB). Some logging drivers can include environment variables or labels in log output. The section lists supported logging drivers and links to their documentation for configurable options. Logging driver plugins may offer additional options.