Splunk logging driver

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The splunk logging driver sends container logs to HTTP Event Collector in Splunk Enterprise and Splunk Cloud.

Usage

You can configure Docker logging to use the splunk driver by default or on a per-container basis.

To use the splunk driver as the default logging driver, set the keys log-driver and log-opts to appropriate values in the daemon.json configuration file and restart Docker. For example:

{
  "log-driver": "splunk",
  "log-opts": {
    "splunk-token": "",
    "splunk-url": "",
    ...
  }
}

The daemon.json file 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.

To use the splunk driver for a specific container, use the commandline flags --log-driver and log-opt with docker run:

  docker run --log-driver=splunk --log-opt splunk-token=VALUE --log-opt splunk-url=VALUE ...

Splunk options

The following properties let you configure the splunk logging driver.

  • To configure the splunk driver across the Docker environment, edit daemon.json with the key, "log-opts": {"NAME": "VALUE", ...}.
  • To configure the splunk driver for an indiviual container, use docker run with the flag, --log-opt NAME=VALUE ....
OptionRequiredDescription
splunk-tokenrequiredSplunk HTTP Event Collector token.
splunk-urlrequiredPath to your Splunk Enterprise, self-service Splunk Cloud instance, or Splunk Cloud managed cluster (including port and scheme used by HTTP Event Collector) in one of the following formats: https://your_splunk_instance:8088 or https://input-prd-p-XXXXXXX.cloud.splunk.com:8088 or https://http-inputs-XXXXXXXX.splunkcloud.com.
splunk-sourceoptionalEvent source.
splunk-sourcetypeoptionalEvent source type.
splunk-indexoptionalEvent index.
splunk-capathoptionalPath to root certificate.
splunk-canameoptionalName to use for validating server certificate; by default the hostname of the splunk-url will be used.
splunk-insecureskipverifyoptionalIgnore server certificate validation.
splunk-formatoptionalMessage format. Can be inline, json or raw. Defaults to inline.
splunk-verify-connectionoptionalVerify on start, that docker can connect to Splunk server. Defaults to true.
splunk-gzipoptionalEnable/disable gzip compression to send events to Splunk Enterprise or Splunk Cloud instance. Defaults to false.
splunk-gzip-leveloptionalSet compression level for gzip. Valid values are -1 (default), 0 (no compression), 1 (best speed) … 9 (best compression). Defaults to DefaultCompression.
tagoptionalSpecify tag for message, which interpret some markup. Default value is {{.ID}} (12 characters of the container ID). Refer to the log tag option documentation for customizing the log tag format.
labelsoptionalComma-separated list of keys of labels, which should be included in message, if these labels are specified for container.
envoptionalComma-separated list of keys of environment variables, which should be included in message, if these variables are specified for container.
env-regexoptionalSimilar to and compatible with env. A regular expression to match logging-related environment variables. Used for advanced log tag options.

If there is collision between the label and env keys, the value of the env takes precedence. Both options add additional fields to the attributes of a logging message.

Below is an example of the logging options specified for the Splunk Enterprise instance. The instance is installed locally on the same machine on which the Docker daemon is running.

The path to the root certificate and Common Name is specified using an HTTPS scheme. This is used for verification. The SplunkServerDefaultCert is automatically generated by Splunk certificates.


$ docker run --log-driver=splunk \
           --log-opt splunk-token=176FCEBF-4CF5-4EDF-91BC-703796522D20 \
           --log-opt splunk-url=https://splunkhost:8088 \
           --log-opt splunk-capath=/path/to/cert/cacert.pem \
           --log-opt splunk-caname=SplunkServerDefaultCert \
           --log-opt tag="{{.Name}}/{{.FullID}}" \
           --log-opt labels=location \
           --log-opt env=TEST \
           --env "TEST=false" \
           --label location=west \
       your/application

The splunk-url for Splunk instances hosted on Splunk Cloud is in a format like https://http-inputs-XXXXXXXX.splunkcloud.com and does not include a port specifier.

Message formats

There are three logging driver messaging formats: inline (default), json, and raw.

The default format is inline where each log message is embedded as a string. For example:

{
    "attrs": {
        "env1": "val1",
        "label1": "label1"
    },
    "tag": "MyImage/MyContainer",
    "source":  "stdout",
    "line": "my message"
}
{
    "attrs": {
        "env1": "val1",
        "label1": "label1"
    },
    "tag": "MyImage/MyContainer",
    "source":  "stdout",
    "line": "{\"foo\": \"bar\"}"
}

Note: If your messages are JSON objects, you may want to embed them in the message we send to Splunk.

To format messages as json objects, set --log-opt splunk-format=json. The driver trys to parse every line as a JSON object and send it as an embedded object. If it cannot parse the message, it is sent inline. For example:

{
    "attrs": {
        "env1": "val1",
        "label1": "label1"
    },
    "tag": "MyImage/MyContainer",
    "source":  "stdout",
    "line": "my message"
}
{
    "attrs": {
        "env1": "val1",
        "label1": "label1"
    },
    "tag": "MyImage/MyContainer",
    "source":  "stdout",
    "line": {
        "foo": "bar"
    }
}

To format messages as raw, set --log-opt splunk-format=raw. Attributes (environment variables and labels) and tags are prefixed to the message. For example:

MyImage/MyContainer env1=val1 label1=label1 my message
MyImage/MyContainer env1=val1 label1=label1 {"foo": "bar"}

Advanced options

Splunk Logging Driver allows you to configure few advanced options by specifying next environment variables for the Docker daemon.

Environment variable nameDefault valueDescription
SPLUNK_LOGGING_DRIVER_POST_MESSAGES_FREQUENCY5sIf there is nothing to batch how often driver will post messages. You can think about this as the maximum time to wait for more messages to batch.
SPLUNK_LOGGING_DRIVER_POST_MESSAGES_BATCH_SIZE1000How many messages driver should wait before sending them in one batch.
SPLUNK_LOGGING_DRIVER_BUFFER_MAX10 * 1000If driver cannot connect to remote server, what is the maximum amount of messages it can hold in buffer for retries.
SPLUNK_LOGGING_DRIVER_CHANNEL_SIZE4 * 1000How many pending messages can be in the channel which is used to send messages to background logger worker, which batches them.
splunk, docker, logging, driver