These docs are for Cribl Stream 4.9 and are no longer actively maintained.

See the latest version (4.13).

Splunk HEC Destination

The Splunk HEC Destination can stream data to a Splunk HEC (HTTP Event Collector) receiver through the event, raw, and S2S endpoints.

The data arrives to Splunk cooked and parsed, so it enters at the Splunk data pipeline’s indexing segment.

Type: Streaming | TLS Support: Yes | PQ Support: Yes

Looking for a quick way to switch all of your S2S Destinations to Splunk HEC Destinations? Follow our how-to guide: Switch Cribl Stream Destinations from S2S to Splunk HEC.

The Splunk HEC Destination is recommended for Splunk Cloud. For details, see Splunk Cloud Platform and BYOL Integrations.

Configure Cribl Stream to Output to Splunk HEC Destinations

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1. On the top bar, select Products, and then select Cribl Stream. Under Worker Groups, select a Worker Group. Next, you have two options:

   • To configure via QuickConnect, navigate to Routing > QuickConnect (Stream) or Collect (Edge). Select Add Destination and select the Destination you want from the list, choosing either Select Existing or Add New.
   • To configure via the Routes, select Data > Destinations or More > Destinations (Edge). Select the Destination you want. Next, select Add Destination.

2. In the New Destination modal, configure the following under General Settings:

   • Output ID: Enter a unique name to identify this Splunk HEC definition. If you clone this Destination, Cribl Stream will add -CLONE to the original Output ID.
   • Description: Optionally, enter a description.
   • Load balancing: When enabled (default), lets you specify multiple Splunk HEC endpoints and load weights. With the default No setting, if you notice that Cribl Stream is not sending data to all possible IP addresses, enable Advanced Settings > Round-robin DNS.
   • Splunk HEC endpoint(s): URLs of Splunk HEC endpoints to send events to.

3. Under Authentication, select an Authentication method from the dropdown:

   • Manual: Displays an HEC Auth token field for you to enter your Splunk HEC token.
   • Secret: This option exposes an HEC Auth token (text secret) drop-down, in which you can select a stored secret that references the HEC token described above. A Create link is available to store a new, reusable secret.

   This Destination does not support Mutual TLS (mTLS).

4. Next, you can configure the following Optional Settings:

   • Exclude current host IPs: This toggle appears when Load balancing is set to Yes. It determines whether to exclude all IPs of the current host from the list of any resolved hostnames. Defaults to No, which keeps the current host available for load balancing.
   • Backpressure behavior: Select whether to block, drop, or queue events when all receivers are exerting backpressure. (Causes might include a broken or denied connection, or a rate limiter.) Defaults to Block.
   • Tags: Optionally, add tags that you can use to filter and group Destinations on the Destinations page. These tags aren’t added to processed events. Use a tab or hard return between (arbitrary) tag names.

5. Optionally, you can adjust the Persistent Queue, Processing, Retries and Advanced settings outlined in the sections below.

   If you’re sending data to Splunk Cloud, Cribl recommends a maximum value of 1 MB for Max body size (KB) under Advanced settings. This upper limit is defined by the maximum content length for the default HTTP Event Collector (HEC) provided by Splunk Cloud.

6. Select Save, then Commit & Deploy.

Splunk HEC Endpoints

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Use the Splunk HEC Endpoints table to specify a known set of receivers on which to load-balance data. The table appears only when Load balancing is toggled to Yes.

To specify more receivers on new rows, click Add Endpoint. Each row provides the following fields:

• HEC Endpoint: Specify the URL to a Splunk HEC endpoint to send events to. See the Splunk documentation for details on getting your URL. For Splunk Cloud endpoints, https protocol is recommended. Supported endpoints include:

  • /services/collector/event (default)
  • /services/collector/raw
  • /services/collector/health
  • /services/collector/s2s

• Load Weight: Set the relative traffic-handling capability for each connection by assigning a weight (> 0). This column accepts arbitrary values, but for best results, assign weights in the same order of magnitude to all connections. Cribl Stream will attempt to distribute traffic to the connections according to their relative weights.

The final column provides an X button to delete any row from the table.

When you first enable load balancing, or if you edit the load weight once your data is load–balanced, give the logic time to settle. The changes might take a few seconds to register.

For details on configuring all these options, see About Load Balancing.

Indexer Acknowledgement

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Do not set Enable Indexer Acknowledgement on the Splunk token. With this setting enabled, Splunk receivers expect the Channel GUID to be passed in, and requests will fail with errors of this form:

channel: output:splunk_cloud_hec
cid: w2
level: error
message: Request failed
reason: Received status code=400, method=POST, url=https://http-inputs-bazookatron.splunkcloud.com/services/collector/event
response: {"text":"Data channel is missing","code":10}
time: 2023-02-14T15:26:03.413Z

Persistent Queue Settings

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The Persistent Queue Settings tab displays when the Backpressure behavior option in General settings is set to Persistent Queue. Persistent queue buffers and preserves incoming events when a downstream Destination has an outage or experiences backpressure.

Before enabling persistent queue, learn more about persistent queue behavior and how to optimize it with your system:

• About Persistent Queues
• Optimize Destination Persistent Queues (dPQ)
• Destination Backpressure Triggers

On Cribl-managed Cloud Workers (with an Enterprise plan), this tab exposes only the destructive Clear Persistent Queue button (described at the end of this section). A maximum queue size of 1 GB disk space is automatically allocated per PQ‑enabled Destination, per Worker Process. The 1 GB limit is on outbound uncompressed data, and no compression is applied to the queue.

This limit is not configurable. If the queue fills up, Cribl Stream/Edge will block outbound data. To configure the queue size, compression, queue-full fallback behavior, and other options below, use a hybrid Group.

Mode: Use this menu to select when Cribl Stream/Edge engages the persistent queue in response to backpressure events from this Destination. The options are:

If a Worker/Edge Node starts with an invalid Mode setting, it automatically switches to Error mode. This might happen if the Worker/Edge Node is running a version that does not support other modes (older than 4.9.0), or if it encounters a nonexistent value in YAML configuration files.

Max file size: The maximum data volume to store in each queue file before closing it. Enter a numeral with units of KB, MB, etc. Defaults to 1 MB.

Max queue size: The maximum amount of disk space that the queue can consume on each Worker Process. When the queue reaches this limit, the Destination stops queueing data and applies the Queue‑full behavior. Defaults to 5 GB. This field accepts positive numbers with units of KB, MB, GB, and so on. You can set it as high as 1 TB, unless you’ve configured a different Max PQ size per Worker Process on the Group Settings/Fleet Settings page.

Queue file path: The location for the persistent queue files. Defaults to $CRIBL_HOME/state/queues. Cribl Stream/Edge will append /<worker‑id>/<output‑id> to this value.

Compression: Set the codec to use when compressing the persisted data after closing a file. Defaults to None. Gzip is also available.

Queue-full behavior: Whether to block or drop events when the queue begins to exert backpressure. A queue begins to exert backpressure when the disk is low or at full capacity. This setting has two options:

• Block: The output will refuse to accept new data until the receiver is ready. The system will return block signals back to the sender.
• Drop new data: Discard all new events until the backpressure event has resolved and the receiver is ready.

Backpressure duration Limit: When Mode is set to Backpressure, this setting controls how long to wait during network slowdowns before activating queues. A shorter duration enhances critical data loss prevention, while a longer duration helps avoid unnecessary queue transitions in environments with frequent, brief network fluctuations. The default value is 30 seconds.

Strict ordering: By default, the Yes setting enables FIFO (first in, first out) event forwarding, ensuring Cribl Stream/Edge sends earlier queued events first when receivers recover. The persistent queue flushes every 10 seconds in this mode. Changing the setting to No allows you to prioritize new events over queued events and configure a custom drain rate for the queue. When No is enabled, this option appears:

• Drain rate limit (EPS): Optionally, set a throttling rate (in events per second) on writing from the queue to receivers. (The default 0 value disables throttling.) Throttling the queue drain rate can boost the throughput of new and active connections by reserving more resources for them. You can further optimize Worker startup connections and CPU load in the Group Settings/Fleet Settings > Worker Processes settings.

Clear Persistent Queue: For Cloud Enterprise only, click this button if you want to delete the files that are currently queued for delivery to this Destination. If you click this button, a confirmation modal appears. Clearing the queue frees up disk space by permanently deleting the queued data, without delivering it to downstream receivers. This button only appears after you define the Output ID.

Use the Clear Persistent Queue button with caution to avoid data loss. See Steps to Safely Disable and Clear Persistent Queues for more information.

Processing Settings

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Post‑Processing

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Pipeline: Pipeline to process data before sending the data out using this output.

System fields: A list of fields to automatically add to events that use this output. By default, includes cribl_pipe (identifying the Cribl Stream Pipeline that processed the event). Supports wildcards. Other options include:

• cribl_host – Cribl Stream Node that processed the event.
• cribl_input – Cribl Stream Source that processed the event.
• cribl_output – Cribl Stream Destination that processed the event.
• cribl_route – Cribl Stream Route (or QuickConnect) that processed the event.
• cribl_wp – Cribl Stream Worker Process that processed the event.

Retries

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Honor Retry-After header: Whether to honor a Retry-After header, provided that the header specifies a delay no longer than 180 seconds. Cribl Stream/Edge limits the delay to 180 seconds even if the Retry-After header specifies a longer delay. When enabled, any Retry-After header received takes precedence over all other options configured in the Retries section. When disabled, all Retry-After headers are ignored.

Settings for failed HTTP requests: When you want to automatically retry requests that receive particular HTTP response status codes, use these settings to list those response codes.

For any HTTP response status codes that are not explicitly configured for retries, Cribl Stream/Edge applies the following rules:

Upon receiving a response code that’s on the list, Cribl Stream/Edge first waits for a set time interval called the Pre-backoff interval and then begins retrying the request. Time between retries increases based on an exponential backoff algorithm whose base is the Backoff multiplier, until the backoff multiplier reaches the Backoff limit (ms). At that point, Cribl Stream/Edge continues retrying the request without increasing the time between retries any further.

If the sender (which manages the connection to the Destination) is at capacity, it will not accept any incoming events. These incoming events originate internally from a previous stage of the data flow when Destinations send outbound requests to their respective external services, and they include retry requests and new requests. Any events that were already in transit when the sender reached capacity will continue to be processed downstream.

Sender capacity is freed up when an outgoing request succeeds or encounters a non-retryable error. When the sender has available capacity again, it will resume accepting incoming events. This capacity management is influenced by the number of active connections and configured limits, such as concurrency and buffer sizes. If a Pipeline sends events faster than the Destination can process, the buffers may fill up, leading to backpressure and Sender at capacity warnings. This backpressure prevents the sender from accepting additional requests until capacity is restored.

By default, this Destination has no response codes configured for automatic retries. For each response code you want to add to the list, select Add Setting and configure the following settings:

• HTTP status code: A response code that indicates a failed request, for example 429 (Too Many Requests) or 503 (Service Unavailable).
• Pre-backoff interval (ms): The amount of time to wait before beginning retries, in milliseconds. Defaults to 1000 (one second).
• Backoff multiplier: The base for the exponential backoff algorithm. A value of 2 (the default) means that Cribl Stream/Edge will retry after 2 seconds, then 4 seconds, then 8 seconds, and so on.
• Backoff limit (ms): The maximum backoff interval Cribl Stream/Edge should apply for its final retry, in milliseconds. Default (and minimum) is 10,000 (10 seconds); maximum is 180,000 (180 seconds, or 3 minutes).

Retry timed-out HTTP requests: When you want to automatically retry requests that have timed out, toggle this control on to display the following settings for configuring retry behavior:

• Pre-backoff interval (ms): The amount of time to wait before beginning retries, in milliseconds. Defaults to 1000 (one second).
• Backoff multiplier: The base for the exponential backoff algorithm. A value of 2 (the default) means that Cribl Stream/Edge will retry after 2 seconds, then 4 seconds, then 8 seconds, and so on.
• Backoff limit (ms): The maximum backoff interval Cribl Stream/Edge should apply for its final retry, in milliseconds. Default (and minimum) is 10,000 (10 seconds); maximum is 180,000 (180 seconds, or 3 minutes).

Advanced Settings

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Output multi–metrics: Toggle to Yes to output multiple-measurement metric data points. (Supported in Splunk 8.0 and above, this format enables sending multiple metrics in a single event, improving the efficiency of your Splunk capacity.)

Validate server certs: Reject certificates that are not authorized by a trusted CA (for example, the system’s CA). Defaults to Yes.

Round–robin DNS: Toggle on to enable round-robin DNS lookup across multiple IP addresses, IPv4 and IPv6. When a DNS server resolves a Fully Qualified Domain Name (FQDN) to multiple IP addresses, Cribl Stream will sequentially use each address in the order they are returned by the DNS server for subsequent connection attempts. (This setting is available only when General Settings > Load balancing is set to No.)

Compress: Compresses the payload body before sending. Defaults to Yes (recommended).

Request timeout: Amount of time (in seconds) to wait for a request to complete before aborting it. Defaults to 30.

Request concurrency: Maximum number of concurrent requests per Worker Process. When Cribl Stream hits this limit, it begins throttling traffic to the downstream service. Defaults to 5. Minimum: 1. Maximum: 32. Each request can potentially hit a different HEC receiver.

Max body size (KB): Maximum size, in KB, of the request body. Defaults to 4096. Lowering the size can potentially result in more parallel requests and also cause outbound requests to be made sooner.

If you’re sending data to Splunk Cloud, Cribl recommends a maximum value of 1 MB for Max body size (KB). This upper limit is defined by the maximum content length for the default HTTP Event Collector (HEC) provided by Splunk Cloud.

Max events per request: Maximum number of events to include in the request body. The 0 default allows unlimited events.

Flush period (sec): Maximum time between requests. Low values can cause the payload size to be smaller than the configured Max body size. Defaults to 1.

• Retries happen on this flush interval.
• Any HTTP response code in the 2xx range is considered success.
• Any response code in the 5xx range is considered a retryable error, which will not trigger Persistent Queue (PQ) usage.
• Any other response code will trigger PQ (if PQ is configured as the Backpressure behavior).

Extra HTTP headers: Click Add Header to add Name/Value pairs to pass as additional HTTP headers. Values will be sent encrypted.

The next two fields appear only when the General Settings > Load balancing option is set to Yes.

DNS resolution period (seconds): Re-resolve any hostnames after each interval of this many seconds, and pick up destinations from A records. Defaults to 600 seconds.

Load balance stats period (seconds): The duration (in seconds) Cribl Stream tracks historical traffic data to influence load balancing decisions. Defaults to 300 seconds. If a hostname resolves to multiple IPs (via DNS A records), all IPs inherit the weight assigned to the hostname unless each IP is explicitly configured with its own weight. Cribl Stream prioritizes IP-specific settings over hostname-derived settings for load balancing.

Failed request logging mode: Use this drop-down to determine which data should be logged when a request fails. Select among None (the default), Payload, or Payload + Headers. With this last option, Cribl Stream will redact all headers, except non-sensitive headers that you declare below in Safe headers.

Safe headers: Add headers to declare them as safe to log in plaintext. (Sensitive headers such as authorization will always be redacted, even if listed here.) Use a tab or hard return to separate header names.

Environment: If you’re using GitOps, optionally use this field to specify a single Git branch on which to enable this configuration. If empty, the config will be enabled everywhere.

Splunk App Settings provides two fields that take effect only in the Cribl App for Splunk. (Cribl Stream ignores their values.)

• Next processing queue: Specify the next Splunk processing queue to send the events to, after HEC processing. Defaults to indexQueue.

• Default _TCP_ROUTING: Specify the value of the _TCP_ROUTING field for events that do not have _ctrl._TCP_ROUTING set. Defaults to nowhere. This is useful only when you expect the HEC receiver to route this data on to another destination.

Notes on HTTP-Based Outputs

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• To proxy outbound HTTP/S requests, see System Proxy Configuration.

• Cribl Stream will attempt to use keepalives to reuse a connection for multiple requests. After two minutes of the first use, the connection will be thrown away, and a new connection will be reattempted. This is to prevent sticking to a particular Destination when there is a constant flow of events.

• If the server does not support keepalives – or if the server closes a pooled connection while idle – a new connection will be established for the next request.

• When resolving the Destination’s hostname with load balancing disabled, Cribl Stream will pick the first IP in the list for use in the next connection. Enable Round-robin DNS to better balance distribution of events between Splunk HEC servers.

• See Splunk’s documentation on editing fields.conf to ensure the visibility of index-time fields sent to Splunk by Cribl Stream.

Troubleshooting

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The Destination’s configuration modal has helpful tabs for troubleshooting:

Live Data: Try capturing live data to see real-time events as they flow through the Destination. On the Live Data tab, click Start Capture to begin viewing real-time data.

Logs: Review and search the logs that provide detailed information about the delivery process, including any errors or warnings that may have occurred.

Test: Ensures that the Destination is correctly set up and reachable. Verify that sample events are sent correctly by clicking Run Test.

You can also view the Monitoring page that provides a comprehensive overview of data volume and rate, helping you identify delivery issues. Analyze the graphs showing events and bytes in/out over time.

Cribl University offers an Advanced Troubleshooting > Destination Integrations: Splunk Cloud short course. To follow the direct course link, first log into your Cribl University account. (To create an account, select the Sign up link. You’ll need to select through a short Terms & Conditions presentation, with chill music, before proceeding to courses – but Cribl’s training is always free of charge.) Once logged in, check out other useful Advanced Troubleshooting short courses and Troubleshooting Criblets.