The gelf logging driver is a convenient format that's understood by a number of tools such as Graylog, Logstash, and Fluentd. Many tools use this format.

In GELF, every log message is a dict with the following fields:

  • Version
  • Host (who sent the message in the first place)
  • Timestamp
  • Short and long version of the message
  • Any custom fields you configure yourself

Usage#

To use the gelf driver as the default logging driver, set the log-driver and log-opt keys to appropriate values in the daemon.json file, which is located in /etc/docker/ on Linux hosts or C:\ProgramData\docker\config\daemon.json on Windows Server. For more about configuring Docker using daemon.json, see daemon.json.

The following example sets the log driver to gelf and sets the gelf-address option.

{
  "log-driver": "gelf",
  "log-opts": {
    "gelf-address": "udp://1.2.3.4:12201"
  }
}

Restart Docker for the changes to take effect.

[!NOTE]

log-opts configuration options in the daemon.json configuration file must be provided as strings. Boolean and numeric values (such as the value for gelf-tcp-max-reconnect) must therefore be enclosed in quotes (").

You can set the logging driver for a specific container by setting the --log-driver flag when using docker container create or docker run:

$ docker run \
      --log-driver gelf --log-opt gelf-address=udp://1.2.3.4:12201 \
      alpine echo hello world

GELF options#

The gelf logging driver supports the following options:

Option Required Description Example value
gelf-address required The address of the GELF server. tcp and udp are the only supported URI specifier and you must specify the port. --log-opt gelf-address=udp://192.168.0.42:12201
gelf-compression-type optional UDP Only The type of compression the GELF driver uses to compress each log message. Allowed values are gzip, zlib and none. The default is gzip. Note that enabled compression leads to excessive CPU usage, so it's highly recommended to set this to none. --log-opt gelf-compression-type=gzip
gelf-compression-level optional UDP Only The level of compression when gzip or zlib is the gelf-compression-type. An integer in the range of -1 to 9 (BestCompression). Default value is 1 (BestSpeed). Higher levels provide more compression at lower speed. Either -1 or 0 disables compression. --log-opt gelf-compression-level=2
gelf-tcp-max-reconnect optional TCP Only The maximum number of reconnection attempts when the connection drop. An positive integer. Default value is 3. --log-opt gelf-tcp-max-reconnect=3
gelf-tcp-reconnect-delay optional TCP Only The number of seconds to wait between reconnection attempts. A positive integer. Default value is 1. --log-opt gelf-tcp-reconnect-delay=1
tag optional A string that's appended to the APP-NAME in the gelf message. By default, Docker uses the first 12 characters of the container ID to tag log messages. Refer to the log tag option documentation for customizing the log tag format. --log-opt tag=mailer
labels optional Applies when starting the Docker daemon. A comma-separated list of logging-related labels this daemon accepts. Adds additional key on the extra fields, prefixed by an underscore (_). Used for advanced log tag options. --log-opt labels=production_status,geo
labels-regex optional Similar to and compatible with labels. A regular expression to match logging-related labels. Used for advanced log tag options. --log-opt labels-regex=^(production_status\|geo)
env optional Applies when starting the Docker daemon. A comma-separated list of logging-related environment variables this daemon accepts. Adds additional key on the extra fields, prefixed by an underscore (_). Used for advanced log tag options. --log-opt env=os,customer
env-regex optional Similar to and compatible with env. A regular expression to match logging-related environment variables. Used for advanced log tag options. --log-opt env-regex=^(os\|customer)

[!NOTE]

The gelf driver doesn't support TLS for TCP connections. Messages sent to TLS-protected inputs can silently fail.

Examples#

This example configures the container to use the GELF server running at 192.168.0.42 on port 12201.

$ docker run -dit \
    --log-driver=gelf \
    --log-opt gelf-address=udp://192.168.0.42:12201 \
    alpine sh