Splunk logging driver

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

Usage

You can configure the default logging driver by passing the --log-driver option to the Docker daemon:

dockerd --log-driver=splunk

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 or Splunk Cloud instance (including port and scheme used by HTTP Event Collector) https://your_splunk_instance:8088.
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.

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

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.