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

To use the splunk 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 splunk.

{
  "log-driver": "splunk"
}

Restart Docker for the changes to take effect.

You can set the logging driver for a specific container by using the --log-driver option to docker run:

docker run --log-driver=splunk ...

Splunk options

You can use the --log-opt NAME=VALUE flag to specify these additional Splunk logging driver options:

Option Required Description
splunk-token required Splunk HTTP Event Collector token.
splunk-url required Path 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-source optional Event source.
splunk-sourcetype optional Event source type.
splunk-index optional Event index.
splunk-capath optional Path to root certificate.
splunk-caname optional Name to use for validating server certificate; by default the hostname of the splunk-url will be used.
splunk-insecureskipverify optional Ignore server certificate validation.
splunk-format optional Message format. Can be inline, json or raw. Defaults to inline.
splunk-verify-connection optional Verify on start, that docker can connect to Splunk server. Defaults to true.
splunk-gzip optional Enable/disable gzip compression to send events to Splunk Enterprise or Splunk Cloud instance. Defaults to false.
splunk-gzip-level optional Set compression level for gzip. Valid values are -1 (default), 0 (no compression), 1 (best speed) … 9 (best compression). Defaults to DefaultCompression.
tag optional Specify 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.
labels optional Comma-separated list of keys of labels, which should be included in message, if these labels are specified for container.
env optional Comma-separated list of keys of environment variables, which should be included in message, if these variables are specified for container.
env-regex optional Similar 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 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 option 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

By default Logging Driver sends messages as inline format, where each message will be 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\"}"
}

In case if your messages are JSON objects you may want to embed them in the message we send to Splunk. By specifying --log-opt splunk-format=json driver will try to parse every line as a JSON object and send it as embedded object. In case if it cannot parse it - message will be send as 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"
    }
}

Third format is a raw message. You can specify it by using --log-opt splunk-format=raw. Attributes (environment variables and labels) and tag will be 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 name Default value Description
SPLUNK_LOGGING_DRIVER_POST_MESSAGES_FREQUENCY 5s If 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_SIZE 1000 How many messages driver should wait before sending them in one batch.
SPLUNK_LOGGING_DRIVER_BUFFER_MAX 10 * 1000 If driver cannot connect to remote server, what is the maximum amount of messages it can hold in buffer for retries.
SPLUNK_LOGGING_DRIVER_CHANNEL_SIZE 4 * 1000 How 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